<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019f3773-13d9-7e79-9be1-7dc3170b3fa3,g:50ca171c-596f-491e-b7de-4abef00d301d-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://harbor.com/role/ConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="hrbr-20251231.xsd#ConsolidatedStatementsofOperations"/>
  <link:definitionLink xlink:role="http://harbor.com/role/ConsolidatedStatementsofOperations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019f3773-14a0-76a9-bea4-81f753802a6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_StatementTable_019f3773-14a0-76a9-bea4-81f753802a6b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019f3773-14a0-7979-9da8-f71d6c3363d4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019f3773-14a0-76a9-bea4-81f753802a6b" xlink:to="loc_srt_ProductOrServiceAxis_019f3773-14a0-7979-9da8-f71d6c3363d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019f3773-14a0-7979-9da8-f71d6c3363d4_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019f3773-14a0-7979-9da8-f71d6c3363d4" xlink:to="loc_srt_ProductsAndServicesDomain_019f3773-14a0-7979-9da8-f71d6c3363d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019f3773-14a0-7e1c-8276-8fc786fcec3d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019f3773-14a0-7979-9da8-f71d6c3363d4" xlink:to="loc_srt_ProductsAndServicesDomain_019f3773-14a0-7e1c-8276-8fc786fcec3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_ContractRevenueMember_019f3773-14a0-7f38-9998-ea0ba5ca2acf" xlink:href="hrbr-20251231.xsd#hrbr_ContractRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019f3773-14a0-7e1c-8276-8fc786fcec3d" xlink:to="loc_hrbr_ContractRevenueMember_019f3773-14a0-7f38-9998-ea0ba5ca2acf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_ContractServiceAndOtherMember_019f3773-14a0-7121-b03f-9135afd8c4f6" xlink:href="hrbr-20251231.xsd#hrbr_ContractServiceAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019f3773-14a0-7e1c-8276-8fc786fcec3d" xlink:to="loc_hrbr_ContractServiceAndOtherMember_019f3773-14a0-7121-b03f-9135afd8c4f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019f3773-14a0-7d12-84d4-87ed32e1e21a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_RevenuesAbstract_019f3773-14a0-7d12-84d4-87ed32e1e21a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_019f3773-14a0-70db-a50b-39e82929efa7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019f3773-14a0-7d12-84d4-87ed32e1e21a" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_019f3773-14a0-70db-a50b-39e82929efa7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019f3773-14a0-7f24-8696-fcb38c8970fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019f3773-14a0-7f24-8696-fcb38c8970fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfessionalAndContractServicesExpense_019f3773-14a0-7c31-abdd-fa0a7111377a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfessionalAndContractServicesExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019f3773-14a0-7f24-8696-fcb38c8970fe" xlink:to="loc_us-gaap_ProfessionalAndContractServicesExpense_019f3773-14a0-7c31-abdd-fa0a7111377a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FuelCosts_019f3773-14a0-79b7-af97-2a45345d60ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FuelCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019f3773-14a0-7f24-8696-fcb38c8970fe" xlink:to="loc_us-gaap_FuelCosts_019f3773-14a0-79b7-af97-2a45345d60ed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AircraftMaintenanceMaterialsAndRepairs_019f3773-14a0-755c-ad08-2a522eba69e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AircraftMaintenanceMaterialsAndRepairs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019f3773-14a0-7f24-8696-fcb38c8970fe" xlink:to="loc_us-gaap_AircraftMaintenanceMaterialsAndRepairs_019f3773-14a0-755c-ad08-2a522eba69e2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_OtherRentalExpenses_019f3773-14a0-767e-8916-fee8fa7d02e5" xlink:href="hrbr-20251231.xsd#hrbr_OtherRentalExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019f3773-14a0-7f24-8696-fcb38c8970fe" xlink:to="loc_hrbr_OtherRentalExpenses_019f3773-14a0-767e-8916-fee8fa7d02e5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_019f3773-14a0-7c12-b247-ab1f593515b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019f3773-14a0-7f24-8696-fcb38c8970fe" xlink:to="loc_us-gaap_DepreciationAndAmortization_019f3773-14a0-7c12-b247-ab1f593515b4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfOtherAssets_01a0575b-ce77-7072-8d88-866e2a33e4c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019f3773-14a0-7f24-8696-fcb38c8970fe" xlink:to="loc_us-gaap_GainLossOnSaleOfOtherAssets_01a0575b-ce77-7072-8d88-866e2a33e4c7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirlineCapacityPurchaseArrangements_019f3773-14a0-7d02-a310-481c0af716d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirlineCapacityPurchaseArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019f3773-14a0-7f24-8696-fcb38c8970fe" xlink:to="loc_us-gaap_AirlineCapacityPurchaseArrangements_019f3773-14a0-7d02-a310-481c0af716d1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019f3773-14a0-737f-9c86-633ed263210a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019f3773-14a0-7f24-8696-fcb38c8970fe" xlink:to="loc_us-gaap_CostsAndExpenses_019f3773-14a0-737f-9c86-633ed263210a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019f3773-14a0-7eff-83d2-78f50110fd7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_OperatingIncomeLoss_019f3773-14a0-7eff-83d2-78f50110fd7a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019f3773-14a0-7c89-b6ca-4a08bf53724c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019f3773-14a0-7c89-b6ca-4a08bf53724c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterestAndDividend_019f3773-14a0-7b6a-a271-7bbe2393472f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterestAndDividend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019f3773-14a0-7c89-b6ca-4a08bf53724c" xlink:to="loc_us-gaap_InvestmentIncomeInterestAndDividend_019f3773-14a0-7b6a-a271-7bbe2393472f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019f3773-14a0-70cc-b1e0-8442fbced962" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019f3773-14a0-7c89-b6ca-4a08bf53724c" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019f3773-14a0-70cc-b1e0-8442fbced962" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_GainLossOnMarketableSecuritiesShortTermRestrictedInvestmentsAndLongTermRestrictedInvestments_019f3773-14a0-73c6-b310-56cd4323d39b" xlink:href="hrbr-20251231.xsd#hrbr_GainLossOnMarketableSecuritiesShortTermRestrictedInvestmentsAndLongTermRestrictedInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019f3773-14a0-7c89-b6ca-4a08bf53724c" xlink:to="loc_hrbr_GainLossOnMarketableSecuritiesShortTermRestrictedInvestmentsAndLongTermRestrictedInvestments_019f3773-14a0-73c6-b310-56cd4323d39b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019f3773-14a0-7953-8fd8-845046650654" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019f3773-14a0-7c89-b6ca-4a08bf53724c" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019f3773-14a0-7953-8fd8-845046650654" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019f3773-14a0-70d6-ad98-eb08b2d557a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019f3773-14a0-7c89-b6ca-4a08bf53724c" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019f3773-14a0-70d6-ad98-eb08b2d557a7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019f3773-14a0-70cb-8d4b-17f30a8d7779" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019f3773-14a0-70cb-8d4b-17f30a8d7779" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019f3773-14a0-7ea4-b102-d9248adcf4f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019f3773-14a0-7ea4-b102-d9248adcf4f8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019f3773-14a0-727e-8710-1f5c49a06311" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_NetIncomeLoss_019f3773-14a0-727e-8710-1f5c49a06311" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityDividendsAdjustment_019f3773-14a0-751d-b996-07be5a205d8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityDividendsAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_TemporaryEquityDividendsAdjustment_019f3773-14a0-751d-b996-07be5a205d8c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_019f3773-14a0-79d1-8ae3-d4395d237677" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_019f3773-14a0-79d1-8ae3-d4395d237677" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019f3773-14a0-7773-b58c-8d793c137089" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_EarningsPerShareBasic_019f3773-14a0-7773-b58c-8d793c137089" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019f3773-14a0-7a31-9e8c-0983d7f19d3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019f3773-14a0-7a31-9e8c-0983d7f19d3f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_BasicAndDilutedEarningsPerShareOtherDisclosuresAbstract_019f3773-14a0-757f-9281-260c11726493" xlink:href="hrbr-20251231.xsd#hrbr_BasicAndDilutedEarningsPerShareOtherDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-7e3f-bb16-9b10c3c9d334" xlink:to="loc_hrbr_BasicAndDilutedEarningsPerShareOtherDisclosuresAbstract_019f3773-14a0-757f-9281-260c11726493" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019f3773-14a0-78a8-a7ec-24de7af02f33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_BasicAndDilutedEarningsPerShareOtherDisclosuresAbstract_019f3773-14a0-757f-9281-260c11726493" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019f3773-14a0-78a8-a7ec-24de7af02f33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019f3773-14a0-780c-83d0-f346bb72b4ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_BasicAndDilutedEarningsPerShareOtherDisclosuresAbstract_019f3773-14a0-757f-9281-260c11726493" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019f3773-14a0-780c-83d0-f346bb72b4ec" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/ConsolidatedStatementsofOperationsParenthetical" xlink:type="simple" xlink:href="hrbr-20251231.xsd#ConsolidatedStatementsofOperationsParenthetical"/>
  <link:definitionLink xlink:role="http://harbor.com/role/ConsolidatedStatementsofOperationsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a11205-da8c-7263-90eb-763f3a26ee3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a11205-da8c-75c3-8323-7159736b2a65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a11205-da8c-7263-90eb-763f3a26ee3b" xlink:to="loc_us-gaap_StatementTable_01a11205-da8c-75c3-8323-7159736b2a65" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a11205-da8c-7dfc-a148-06843d15ac38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a11205-da8c-75c3-8323-7159736b2a65" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a11205-da8c-7dfc-a148-06843d15ac38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a11205-da8c-7dfc-a148-06843d15ac38_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a11205-da8c-7dfc-a148-06843d15ac38" xlink:to="loc_us-gaap_RelatedPartyDomain_01a11205-da8c-7dfc-a148-06843d15ac38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a11205-da8c-7d55-996f-76f07d930139" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a11205-da8c-7dfc-a148-06843d15ac38" xlink:to="loc_us-gaap_RelatedPartyDomain_01a11205-da8c-7d55-996f-76f07d930139" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a11206-17e8-74a8-be6f-83b8ec9d0b4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a11205-da8c-7d55-996f-76f07d930139" xlink:to="loc_us-gaap_RelatedPartyMember_01a11206-17e8-74a8-be6f-83b8ec9d0b4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirlineCapacityPurchaseArrangements_01a11205-da8c-7be2-831d-6ec6b7f9eb7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirlineCapacityPurchaseArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a11205-da8c-7263-90eb-763f3a26ee3b" xlink:to="loc_us-gaap_AirlineCapacityPurchaseArrangements_01a11205-da8c-7be2-831d-6ec6b7f9eb7a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="hrbr-20251231.xsd#ConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://harbor.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019f3773-14a0-792d-8c60-f9ab72d07cdb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019f3773-14a0-79dd-b136-fe07d8349157" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-792d-8c60-f9ab72d07cdb" xlink:to="loc_us-gaap_StatementTable_019f3773-14a0-79dd-b136-fe07d8349157" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019f3773-14a0-7c64-8f94-8c22dec40de8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019f3773-14a0-79dd-b136-fe07d8349157" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019f3773-14a0-7c64-8f94-8c22dec40de8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019f3773-14a0-7c64-8f94-8c22dec40de8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019f3773-14a0-7c64-8f94-8c22dec40de8" xlink:to="loc_us-gaap_EquityComponentDomain_019f3773-14a0-7c64-8f94-8c22dec40de8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019f3773-14a0-762b-86e8-7904664cd351" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019f3773-14a0-7c64-8f94-8c22dec40de8" xlink:to="loc_us-gaap_EquityComponentDomain_019f3773-14a0-762b-86e8-7904664cd351" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019f3773-14a0-7d2b-bcb5-08d943e6144e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019f3773-14a0-762b-86e8-7904664cd351" xlink:to="loc_us-gaap_CommonStockMember_019f3773-14a0-7d2b-bcb5-08d943e6144e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019f3773-14a0-73be-b337-383463dcfaad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019f3773-14a0-762b-86e8-7904664cd351" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019f3773-14a0-73be-b337-383463dcfaad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019f3773-14a0-76d3-b5e1-4660cffcc09d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019f3773-14a0-762b-86e8-7904664cd351" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019f3773-14a0-76d3-b5e1-4660cffcc09d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019f3773-14a0-7ba0-b281-bed097591ec3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019f3773-14a0-762b-86e8-7904664cd351" xlink:to="loc_us-gaap_RetainedEarningsMember_019f3773-14a0-7ba0-b281-bed097591ec3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_RepurchasedStockMember_019f3773-14a0-7782-b912-013842c9bc1b" xlink:href="hrbr-20251231.xsd#hrbr_RepurchasedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019f3773-14a0-762b-86e8-7904664cd351" xlink:to="loc_hrbr_RepurchasedStockMember_019f3773-14a0-7782-b912-013842c9bc1b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019f3773-14a0-77fd-8b72-d2d68317c799" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-792d-8c60-f9ab72d07cdb" xlink:to="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019f3773-14a0-77fd-8b72-d2d68317c799" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019f3773-14a0-77be-9a92-ff9a799a12ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019f3773-14a0-77fd-8b72-d2d68317c799" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_019f3773-14a0-77be-9a92-ff9a799a12ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019f600e-6852-75d2-a7c5-806bacef5532" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019f3773-14a0-77fd-8b72-d2d68317c799" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019f600e-6852-75d2-a7c5-806bacef5532" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TemporaryEquityPreferredStockConversionShares_019f3773-14a0-778f-a24c-e6b1e853c42b" xlink:href="hrbr-20251231.xsd#hrbr_TemporaryEquityPreferredStockConversionShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019f3773-14a0-77fd-8b72-d2d68317c799" xlink:to="loc_hrbr_TemporaryEquityPreferredStockConversionShares_019f3773-14a0-778f-a24c-e6b1e853c42b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TemporaryEquityPreferredStockConversionAmount_019f3773-14a0-7998-a9be-f42fd182ac55" xlink:href="hrbr-20251231.xsd#hrbr_TemporaryEquityPreferredStockConversionAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019f3773-14a0-77fd-8b72-d2d68317c799" xlink:to="loc_hrbr_TemporaryEquityPreferredStockConversionAmount_019f3773-14a0-7998-a9be-f42fd182ac55" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TemporaryEquityPreferredStockRedemptionShares_019f6018-96bd-7e05-b074-3c86455e59b9" xlink:href="hrbr-20251231.xsd#hrbr_TemporaryEquityPreferredStockRedemptionShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019f3773-14a0-77fd-8b72-d2d68317c799" xlink:to="loc_hrbr_TemporaryEquityPreferredStockRedemptionShares_019f6018-96bd-7e05-b074-3c86455e59b9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TemporaryEquityPreferredStockRedemptionAmount_019f3773-14a0-7538-aa8c-82f9a8b2ba0f" xlink:href="hrbr-20251231.xsd#hrbr_TemporaryEquityPreferredStockRedemptionAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_019f3773-14a0-77fd-8b72-d2d68317c799" xlink:to="loc_hrbr_TemporaryEquityPreferredStockRedemptionAmount_019f3773-14a0-7538-aa8c-82f9a8b2ba0f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019f3773-14a0-7c0d-bc9a-f3f2d940b74f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_019f6017-9f20-758c-8307-1462917cac03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019f3773-14a0-792d-8c60-f9ab72d07cdb" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019f3773-14a0-782b-a3d8-5630fba64c8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019f3773-14a0-782b-a3d8-5630fba64c8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019f3773-14a0-7895-b20f-e1f89ceb4137" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019f3773-14a0-7895-b20f-e1f89ceb4137" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019f3773-14a0-792a-8247-80a540876361" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:to="loc_us-gaap_StockholdersEquity_019f3773-14a0-792a-8247-80a540876361" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019f3773-14a0-7407-9230-47f79f21d50e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:to="loc_us-gaap_NetIncomeLoss_019f3773-14a0-7407-9230-47f79f21d50e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings_019f3773-14a0-751b-85ee-7d986fee6123" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings_019f3773-14a0-751b-85ee-7d986fee6123" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019f3773-14a0-7cfa-9e8c-cdc024a90720" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019f3773-14a0-7cfa-9e8c-cdc024a90720" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_019f3773-14a0-79dd-8128-aa4399fa8a19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_019f3773-14a0-79dd-8128-aa4399fa8a19" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_019f3773-14a0-76af-a9d8-a3c983675486" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_019f3773-14a0-76af-a9d8-a3c983675486" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019f3773-14a0-7e62-9501-882c61629b0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019f3773-14a0-7d18-a15e-8d10dac0c6e6" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019f3773-14a0-7e62-9501-882c61629b0b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019f3773-14a0-7ca7-8930-f7c7db2c9c98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019f3773-14a0-798f-a091-1b2e1ef3c088" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019f3773-14a0-72c8-9736-889fe2f8ffc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesAviationDispositionDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesAviationDispositionDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesAviationDispositionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057cf-aa94-7a98-b8c1-76256b7d8772" xlink:href="hrbr-20251231.xsd#hrbr_SummaryOfSignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_01a057ce-061b-78e1-bc38-cacfbb73d822" xlink:href="hrbr-20251231.xsd#hrbr_SummaryOfSignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057cf-aa94-7a98-b8c1-76256b7d8772" xlink:to="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_01a057ce-061b-78e1-bc38-cacfbb73d822" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a057cf-aa94-719e-802c-9557e5c03db2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_01a057ce-061b-78e1-bc38-cacfbb73d822" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a057cf-aa94-719e-802c-9557e5c03db2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a057cf-aa94-719e-802c-9557e5c03db2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a057cf-aa94-719e-802c-9557e5c03db2" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a057cf-aa94-719e-802c-9557e5c03db2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a057cf-aa94-7a53-bb59-eb64497683e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a057cf-aa94-719e-802c-9557e5c03db2" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a057cf-aa94-7a53-bb59-eb64497683e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_01a057cf-aa94-7803-a294-7ce97c29f363" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_01a057cf-aa94-7a53-bb59-eb64497683e4" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_01a057cf-aa94-7803-a294-7ce97c29f363" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a057cf-aa94-7ecf-8e93-7b729610a7cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_01a057ce-061b-78e1-bc38-cacfbb73d822" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a057cf-aa94-7ecf-8e93-7b729610a7cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a057cf-aa94-7ecf-8e93-7b729610a7cd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a057cf-aa94-7ecf-8e93-7b729610a7cd" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a057cf-aa94-7ecf-8e93-7b729610a7cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a057cf-aa94-7ddb-9f96-f9bc75fcffa8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a057cf-aa94-7ecf-8e93-7b729610a7cd" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a057cf-aa94-7ddb-9f96-f9bc75fcffa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AviationDispositionMember_01a057cf-aa94-7f38-9b55-58d35230f56a" xlink:href="hrbr-20251231.xsd#hrbr_AviationDispositionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a057cf-aa94-7ddb-9f96-f9bc75fcffa8" xlink:to="loc_hrbr_AviationDispositionMember_01a057cf-aa94-7f38-9b55-58d35230f56a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_01a057cf-aa94-7c1c-8d49-fc5574cb2439" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_01a057ce-061b-78e1-bc38-cacfbb73d822" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_01a057cf-aa94-7c1c-8d49-fc5574cb2439" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a057cf-aa94-7c1c-8d49-fc5574cb2439_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a057cf-aa94-7c1c-8d49-fc5574cb2439" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a057cf-aa94-7c1c-8d49-fc5574cb2439_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a057cf-aa94-7787-bb21-eeb7f1d7f0a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a057cf-aa94-7c1c-8d49-fc5574cb2439" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a057cf-aa94-7787-bb21-eeb7f1d7f0a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_01a057cf-aa94-7f80-9b43-4cc09f47c157" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_01a057cf-aa94-7787-bb21-eeb7f1d7f0a9" xlink:to="loc_us-gaap_SubsequentEventMember_01a057cf-aa94-7f80-9b43-4cc09f47c157" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a0c223-51fb-723a-a2be-65192f28d176" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_01a057ce-061b-78e1-bc38-cacfbb73d822" xlink:to="loc_srt_RangeAxis_01a0c223-51fb-723a-a2be-65192f28d176" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a0c223-51fb-723a-a2be-65192f28d176_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a0c223-51fb-723a-a2be-65192f28d176" xlink:to="loc_srt_RangeMember_01a0c223-51fb-723a-a2be-65192f28d176_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a0c223-51fb-7f31-a8fa-207ad6066aff" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a0c223-51fb-723a-a2be-65192f28d176" xlink:to="loc_srt_RangeMember_01a0c223-51fb-7f31-a8fa-207ad6066aff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a0c223-adf1-70bc-bccb-8433a2543bb4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a0c223-51fb-7f31-a8fa-207ad6066aff" xlink:to="loc_srt_MinimumMember_01a0c223-adf1-70bc-bccb-8433a2543bb4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a0c223-f40d-7df0-9641-fbc9b1a96a8b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a0c223-51fb-7f31-a8fa-207ad6066aff" xlink:to="loc_srt_MaximumMember_01a0c223-f40d-7df0-9641-fbc9b1a96a8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_01a0c46e-1333-740a-a592-02b567b36ad8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057cf-aa94-7a98-b8c1-76256b7d8772" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_01a0c46e-1333-740a-a592-02b567b36ad8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_01a057cf-aa94-7337-a43f-37aa5631df39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057cf-aa94-7a98-b8c1-76256b7d8772" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_01a057cf-aa94-7337-a43f-37aa5631df39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_DisposalGroupIncludingDiscontinuedOperationConsiderationTaxObligationEstimates_01a0c21b-4d8a-7897-b1ac-1309487f8f9c" xlink:href="hrbr-20251231.xsd#hrbr_DisposalGroupIncludingDiscontinuedOperationConsiderationTaxObligationEstimates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057cf-aa94-7a98-b8c1-76256b7d8772" xlink:to="loc_hrbr_DisposalGroupIncludingDiscontinuedOperationConsiderationTaxObligationEstimates_01a0c21b-4d8a-7897-b1ac-1309487f8f9c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesDescriptionofOperationsOutOfPeriodAdjustmentandSegmentReportingDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesDescriptionofOperationsOutOfPeriodAdjustmentandSegmentReportingDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesDescriptionofOperationsOutOfPeriodAdjustmentandSegmentReportingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_01a057d0-2647-7ffa-b19d-1eb45554b37f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-14a1-7032-a801-a1e0c8a87e7f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a057d0-2647-7ffa-b19d-1eb45554b37f" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-14a1-7032-a801-a1e0c8a87e7f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementAxis_01a057d0-2647-7343-8007-d9d8fc35126d" xlink:href="hrbr-20251231.xsd#hrbr_AgreementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-14a1-7032-a801-a1e0c8a87e7f" xlink:to="loc_hrbr_AgreementAxis_01a057d0-2647-7343-8007-d9d8fc35126d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementDomain_01a057d0-2647-7343-8007-d9d8fc35126d_default" xlink:href="hrbr-20251231.xsd#hrbr_AgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_hrbr_AgreementAxis_01a057d0-2647-7343-8007-d9d8fc35126d" xlink:to="loc_hrbr_AgreementDomain_01a057d0-2647-7343-8007-d9d8fc35126d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementDomain_01a057d0-2647-7e7d-ae2e-50473d6e3434" xlink:href="hrbr-20251231.xsd#hrbr_AgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_hrbr_AgreementAxis_01a057d0-2647-7343-8007-d9d8fc35126d" xlink:to="loc_hrbr_AgreementDomain_01a057d0-2647-7e7d-ae2e-50473d6e3434" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AmericanCapacityPurchaseAgreementMember_01a057d0-2647-7d7c-843e-2210b7666ee9" xlink:href="hrbr-20251231.xsd#hrbr_AmericanCapacityPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_AgreementDomain_01a057d0-2647-7e7d-ae2e-50473d6e3434" xlink:to="loc_hrbr_AmericanCapacityPurchaseAgreementMember_01a057d0-2647-7d7c-843e-2210b7666ee9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a057d0-2647-77de-ae51-1cffce77f873" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-14a1-7032-a801-a1e0c8a87e7f" xlink:to="loc_srt_CounterpartyNameAxis_01a057d0-2647-77de-ae51-1cffce77f873" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057d0-2647-77de-ae51-1cffce77f873_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a057d0-2647-77de-ae51-1cffce77f873" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057d0-2647-77de-ae51-1cffce77f873_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057d0-2647-76d0-9689-54b8b8c557d3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a057d0-2647-77de-ae51-1cffce77f873" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057d0-2647-76d0-9689-54b8b8c557d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AirWisconsinMember_01a057d0-2647-72d4-9ab2-4d08496c5ec0" xlink:href="hrbr-20251231.xsd#hrbr_AirWisconsinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057d0-2647-76d0-9689-54b8b8c557d3" xlink:to="loc_hrbr_AirWisconsinMember_01a057d0-2647-72d4-9ab2-4d08496c5ec0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a057d0-2647-77f5-a9dc-bdb1604843c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-14a1-7032-a801-a1e0c8a87e7f" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a057d0-2647-77f5-a9dc-bdb1604843c6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a057d0-2647-77f5-a9dc-bdb1604843c6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a057d0-2647-77f5-a9dc-bdb1604843c6" xlink:to="loc_us-gaap_RelatedPartyDomain_01a057d0-2647-77f5-a9dc-bdb1604843c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a057d0-2647-7903-984c-dbf7b13003d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a057d0-2647-77f5-a9dc-bdb1604843c6" xlink:to="loc_us-gaap_RelatedPartyDomain_01a057d0-2647-7903-984c-dbf7b13003d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a057d0-2647-7a24-a44a-e4f62ac33678" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a057d0-2647-7903-984c-dbf7b13003d2" xlink:to="loc_us-gaap_RelatedPartyMember_01a057d0-2647-7a24-a44a-e4f62ac33678" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a057d0-2647-7af5-b8ef-f40600965529" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-14a1-7032-a801-a1e0c8a87e7f" xlink:to="loc_dei_LegalEntityAxis_01a057d0-2647-7af5-b8ef-f40600965529" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a057d0-2647-7af5-b8ef-f40600965529_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a057d0-2647-7af5-b8ef-f40600965529" xlink:to="loc_dei_EntityDomain_01a057d0-2647-7af5-b8ef-f40600965529_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a057d0-2647-76a1-a9a1-a7030769bfe7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a057d0-2647-7af5-b8ef-f40600965529" xlink:to="loc_dei_EntityDomain_01a057d0-2647-76a1-a9a1-a7030769bfe7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AmericanAirlinesIncMember_01a057d0-2647-7719-bdbb-03448a78ffee" xlink:href="hrbr-20251231.xsd#hrbr_AmericanAirlinesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a057d0-2647-76a1-a9a1-a7030769bfe7" xlink:to="loc_hrbr_AmericanAirlinesIncMember_01a057d0-2647-7719-bdbb-03448a78ffee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AirlineServicesProvidedPeriod_01a08686-1984-71fd-b83c-0e545c85a884" xlink:href="hrbr-20251231.xsd#hrbr_AirlineServicesProvidedPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a057d0-2647-7ffa-b19d-1eb45554b37f" xlink:to="loc_hrbr_AirlineServicesProvidedPeriod_01a08686-1984-71fd-b83c-0e545c85a884" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_NumberOfAircraftRemovedFromService_01a057d0-2647-7457-85df-ec3cd38de3fd" xlink:href="hrbr-20251231.xsd#hrbr_NumberOfAircraftRemovedFromService"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a057d0-2647-7ffa-b19d-1eb45554b37f" xlink:to="loc_hrbr_NumberOfAircraftRemovedFromService_01a057d0-2647-7457-85df-ec3cd38de3fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfAircraftOperated_01a057d0-2647-74b3-bf26-9cdd88210abd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfAircraftOperated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a057d0-2647-7ffa-b19d-1eb45554b37f" xlink:to="loc_us-gaap_NumberOfAircraftOperated_01a057d0-2647-74b3-bf26-9cdd88210abd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_01a057d0-60e5-75d9-ad15-6696a0b1034b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a057d0-2647-7ffa-b19d-1eb45554b37f" xlink:to="loc_us-gaap_NumberOfReportableSegments_01a057d0-60e5-75d9-ad15-6696a0b1034b" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesContractRevenuesDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesContractRevenuesDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesContractRevenuesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:href="hrbr-20251231.xsd#hrbr_SummaryOfSignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f3773-14a1-7dc3-83bb-4b8ee770c691" xlink:href="hrbr-20251231.xsd#hrbr_SummaryOfSignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f3773-14a1-7dc3-83bb-4b8ee770c691" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementAxis_01a057de-c5b8-79a3-957d-aa4e8d45fb27" xlink:href="hrbr-20251231.xsd#hrbr_AgreementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f3773-14a1-7dc3-83bb-4b8ee770c691" xlink:to="loc_hrbr_AgreementAxis_01a057de-c5b8-79a3-957d-aa4e8d45fb27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementDomain_01a057de-c5b8-79a3-957d-aa4e8d45fb27_default" xlink:href="hrbr-20251231.xsd#hrbr_AgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_hrbr_AgreementAxis_01a057de-c5b8-79a3-957d-aa4e8d45fb27" xlink:to="loc_hrbr_AgreementDomain_01a057de-c5b8-79a3-957d-aa4e8d45fb27_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementDomain_01a057de-c5b8-715e-849a-e8f84a029757" xlink:href="hrbr-20251231.xsd#hrbr_AgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_hrbr_AgreementAxis_01a057de-c5b8-79a3-957d-aa4e8d45fb27" xlink:to="loc_hrbr_AgreementDomain_01a057de-c5b8-715e-849a-e8f84a029757" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AmericanCapacityPurchaseAgreementMember_01a057de-c5b8-7ceb-98b3-da54f702e634" xlink:href="hrbr-20251231.xsd#hrbr_AmericanCapacityPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_AgreementDomain_01a057de-c5b8-715e-849a-e8f84a029757" xlink:to="loc_hrbr_AmericanCapacityPurchaseAgreementMember_01a057de-c5b8-7ceb-98b3-da54f702e634" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a057de-c5b8-7dec-a774-e960d002646a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f3773-14a1-7dc3-83bb-4b8ee770c691" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a057de-c5b8-7dec-a774-e960d002646a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a057de-c5b8-7dec-a774-e960d002646a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a057de-c5b8-7dec-a774-e960d002646a" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a057de-c5b8-7dec-a774-e960d002646a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a057de-c5b8-7b37-9b87-5621467f155e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a057de-c5b8-7dec-a774-e960d002646a" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a057de-c5b8-7b37-9b87-5621467f155e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_01a057de-c5b8-77a6-9fab-d54d1341f60e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a057de-c5b8-7b37-9b87-5621467f155e" xlink:to="loc_us-gaap_SalesRevenueNetMember_01a057de-c5b8-77a6-9fab-d54d1341f60e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a057de-c5b8-745b-9912-964ca4988377" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f3773-14a1-7dc3-83bb-4b8ee770c691" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a057de-c5b8-745b-9912-964ca4988377" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a057de-c5b8-745b-9912-964ca4988377_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a057de-c5b8-745b-9912-964ca4988377" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a057de-c5b8-745b-9912-964ca4988377_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a057de-c5b8-7b09-a817-53933f6f8db5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a057de-c5b8-745b-9912-964ca4988377" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a057de-c5b8-7b09-a817-53933f6f8db5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_01a057de-c5b8-7aef-9acc-209fae48bf12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a057de-c5b8-7b09-a817-53933f6f8db5" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_01a057de-c5b8-7aef-9acc-209fae48bf12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_01a057e0-a7bb-7373-acf9-539cdee22605" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a057de-c5b8-7b09-a817-53933f6f8db5" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_01a057e0-a7bb-7373-acf9-539cdee22605" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a057df-2230-7585-b6db-120fef888a02" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f3773-14a1-7dc3-83bb-4b8ee770c691" xlink:to="loc_srt_CounterpartyNameAxis_01a057df-2230-7585-b6db-120fef888a02" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057df-2230-7585-b6db-120fef888a02_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a057df-2230-7585-b6db-120fef888a02" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057df-2230-7585-b6db-120fef888a02_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057df-2230-711b-b989-f9aa8b195943" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a057df-2230-7585-b6db-120fef888a02" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057df-2230-711b-b989-f9aa8b195943" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AirWisconsinMember_01a057df-2230-781a-b0e5-d6f9fe441b3e" xlink:href="hrbr-20251231.xsd#hrbr_AirWisconsinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057df-2230-711b-b989-f9aa8b195943" xlink:to="loc_hrbr_AirWisconsinMember_01a057df-2230-781a-b0e5-d6f9fe441b3e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AmericanAirlinesIncMember_01a057df-49d5-7527-99b6-98854fc35858" xlink:href="hrbr-20251231.xsd#hrbr_AmericanAirlinesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a057df-2230-711b-b989-f9aa8b195943" xlink:to="loc_hrbr_AmericanAirlinesIncMember_01a057df-49d5-7527-99b6-98854fc35858" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a057df-49d5-7543-a8c2-1daaab89b4ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f3773-14a1-7dc3-83bb-4b8ee770c691" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a057df-49d5-7543-a8c2-1daaab89b4ac" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a057df-49d5-7543-a8c2-1daaab89b4ac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a057df-49d5-7543-a8c2-1daaab89b4ac" xlink:to="loc_us-gaap_RelatedPartyDomain_01a057df-49d5-7543-a8c2-1daaab89b4ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a057df-49d5-73f4-8bc4-92ce09156deb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a057df-49d5-7543-a8c2-1daaab89b4ac" xlink:to="loc_us-gaap_RelatedPartyDomain_01a057df-49d5-73f4-8bc4-92ce09156deb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a057df-49d5-7a61-942f-89f0fb493b2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a057df-49d5-73f4-8bc4-92ce09156deb" xlink:to="loc_us-gaap_RelatedPartyMember_01a057df-49d5-7a61-942f-89f0fb493b2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a057df-49d5-7f24-bb30-1f9c45652b66" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f3773-14a1-7dc3-83bb-4b8ee770c691" xlink:to="loc_dei_LegalEntityAxis_01a057df-49d5-7f24-bb30-1f9c45652b66" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a057df-49d5-7f24-bb30-1f9c45652b66_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a057df-49d5-7f24-bb30-1f9c45652b66" xlink:to="loc_dei_EntityDomain_01a057df-49d5-7f24-bb30-1f9c45652b66_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a057df-49d5-7ecf-a14e-bd19f2d569bd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a057df-49d5-7f24-bb30-1f9c45652b66" xlink:to="loc_dei_EntityDomain_01a057df-49d5-7ecf-a14e-bd19f2d569bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AirWisconsinMember_01a057e1-c79b-7a5c-988d-2f72da78c240" xlink:href="hrbr-20251231.xsd#hrbr_AirWisconsinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a057df-49d5-7ecf-a14e-bd19f2d569bd" xlink:to="loc_hrbr_AirWisconsinMember_01a057e1-c79b-7a5c-988d-2f72da78c240" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a057df-c3db-72db-ace5-473b6ada75e2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f3773-14a1-7dc3-83bb-4b8ee770c691" xlink:to="loc_srt_ProductOrServiceAxis_01a057df-c3db-72db-ace5-473b6ada75e2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a057df-c3db-72db-ace5-473b6ada75e2_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_01a057df-c3db-72db-ace5-473b6ada75e2" xlink:to="loc_srt_ProductsAndServicesDomain_01a057df-c3db-72db-ace5-473b6ada75e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a057df-c3db-7fb1-ba6a-f323a90a015c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_01a057df-c3db-72db-ace5-473b6ada75e2" xlink:to="loc_srt_ProductsAndServicesDomain_01a057df-c3db-7fb1-ba6a-f323a90a015c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_HeavyMaintenanceReimbursementsMember_01a057df-c3db-76f1-b007-7bc54e548d48" xlink:href="hrbr-20251231.xsd#hrbr_HeavyMaintenanceReimbursementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a057df-c3db-7fb1-ba6a-f323a90a015c" xlink:to="loc_hrbr_HeavyMaintenanceReimbursementsMember_01a057df-c3db-76f1-b007-7bc54e548d48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_MinimumCrewAvailabilityMember_01a057df-f08b-7d3a-b8ce-55e1ec2db72e" xlink:href="hrbr-20251231.xsd#hrbr_MinimumCrewAvailabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a057df-c3db-7fb1-ba6a-f323a90a015c" xlink:to="loc_hrbr_MinimumCrewAvailabilityMember_01a057df-f08b-7d3a-b8ce-55e1ec2db72e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_FixedDailyRevenueMember_01a057e0-5bdb-7db9-8396-acc1b1eb5c03" xlink:href="hrbr-20251231.xsd#hrbr_FixedDailyRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a057df-c3db-7fb1-ba6a-f323a90a015c" xlink:to="loc_hrbr_FixedDailyRevenueMember_01a057e0-5bdb-7db9-8396-acc1b1eb5c03" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_OnDemandCharterServiceMember_01a057e0-a7bb-7612-9e2e-52657f22046e" xlink:href="hrbr-20251231.xsd#hrbr_OnDemandCharterServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a057df-c3db-7fb1-ba6a-f323a90a015c" xlink:to="loc_hrbr_OnDemandCharterServiceMember_01a057e0-a7bb-7612-9e2e-52657f22046e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_ContractRevenueMember_01a057e0-a7bb-7a38-aba6-6f81811b1365" xlink:href="hrbr-20251231.xsd#hrbr_ContractRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a057df-c3db-7fb1-ba6a-f323a90a015c" xlink:to="loc_hrbr_ContractRevenueMember_01a057e0-a7bb-7a38-aba6-6f81811b1365" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a057de-c5b8-7b38-a351-f506a098c2a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a057de-c5b8-7b38-a351-f506a098c2a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirlineCapacityPurchaseArrangements_01a057df-2230-7f02-bcbc-fac2cfc043e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirlineCapacityPurchaseArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_us-gaap_AirlineCapacityPurchaseArrangements_01a057df-2230-7f02-bcbc-fac2cfc043e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivablesNetCurrent_01a057df-49d5-75e0-9868-803b20790a91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivablesNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_us-gaap_ReceivablesNetCurrent_01a057df-49d5-75e0-9868-803b20790a91" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_RebatesPayable_01a057df-49d5-7433-86c5-e03afe2b0698" xlink:href="hrbr-20251231.xsd#hrbr_RebatesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_hrbr_RebatesPayable_01a057df-49d5-7433-86c5-e03afe2b0698" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_DeferredRevenueRecognition_01a057df-76d1-739e-bad2-c722dcfada7b" xlink:href="hrbr-20251231.xsd#hrbr_DeferredRevenueRecognition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_hrbr_DeferredRevenueRecognition_01a057df-76d1-739e-bad2-c722dcfada7b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_NonrefundableUpfrontFeeRevenues_01a057df-a394-7876-aa6b-57f0a98a5d93" xlink:href="hrbr-20251231.xsd#hrbr_NonrefundableUpfrontFeeRevenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_hrbr_NonrefundableUpfrontFeeRevenues_01a057df-a394-7876-aa6b-57f0a98a5d93" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenueCurrent_01a057df-a394-7132-8e7c-01e6063fb1ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredRevenueCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_us-gaap_DeferredRevenueCurrent_01a057df-a394-7132-8e7c-01e6063fb1ec" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_RevenueFromHeavyMaintenanceServicesAndSupportFeeRecognized_01a057df-c3db-70c8-a096-3cbdfc4ee892" xlink:href="hrbr-20251231.xsd#hrbr_RevenueFromHeavyMaintenanceServicesAndSupportFeeRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_hrbr_RevenueFromHeavyMaintenanceServicesAndSupportFeeRecognized_01a057df-c3db-70c8-a096-3cbdfc4ee892" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_01a057df-c3db-7da5-88a2-cba43ac12460" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_01a057df-c3db-7da5-88a2-cba43ac12460" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_UpfrontFeeReceivedFromMinimumCrewAvailability_01a057df-f08b-722b-9dd7-d6c334471fc7" xlink:href="hrbr-20251231.xsd#hrbr_UpfrontFeeReceivedFromMinimumCrewAvailability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_hrbr_UpfrontFeeReceivedFromMinimumCrewAvailability_01a057df-f08b-722b-9dd7-d6c334471fc7" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_RevenueFromCrewAvailabilityMinimums_01a057df-f08b-70dd-9b66-c6d1ff16ad10" xlink:href="hrbr-20251231.xsd#hrbr_RevenueFromCrewAvailabilityMinimums"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_hrbr_RevenueFromCrewAvailabilityMinimums_01a057df-f08b-70dd-9b66-c6d1ff16ad10" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a057e0-19a2-796f-9ff8-4c606a182f2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a057e0-19a2-796f-9ff8-4c606a182f2c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_01a057e0-5bdb-770c-a638-8e27dea1cff5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_01a057e0-5bdb-770c-a638-8e27dea1cff5" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_01a057e0-a7bb-7a43-a29e-a059a162f062" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_01a057de-c5b8-7446-b075-1ca166a28784" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_01a057e0-a7bb-7a43-a29e-a059a162f062" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesContractServicesandOtherRevenuesDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesContractServicesandOtherRevenuesDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesContractServicesandOtherRevenuesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_01a057d6-a765-73ed-8903-0d2230d1f0b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_01a057d6-a765-7d4d-9058-28a2d25ffffa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_01a057d6-a765-73ed-8903-0d2230d1f0b3" xlink:to="loc_us-gaap_ConcentrationRiskTable_01a057d6-a765-7d4d-9058-28a2d25ffffa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a057d6-a765-7c9b-b46f-3f410457d322" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_01a057d6-a765-7d4d-9058-28a2d25ffffa" xlink:to="loc_srt_ProductOrServiceAxis_01a057d6-a765-7c9b-b46f-3f410457d322" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a057d6-a765-7c9b-b46f-3f410457d322_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_01a057d6-a765-7c9b-b46f-3f410457d322" xlink:to="loc_srt_ProductsAndServicesDomain_01a057d6-a765-7c9b-b46f-3f410457d322_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a057d6-a765-7800-9d55-475951b32bf4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_01a057d6-a765-7c9b-b46f-3f410457d322" xlink:to="loc_srt_ProductsAndServicesDomain_01a057d6-a765-7800-9d55-475951b32bf4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_01a057d6-a765-7124-8696-62ecc36ed3d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a057d6-a765-7800-9d55-475951b32bf4" xlink:to="loc_us-gaap_ServiceMember_01a057d6-a765-7124-8696-62ecc36ed3d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a057d6-a765-7aef-843f-39f50fe0565b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_01a057d6-a765-7d4d-9058-28a2d25ffffa" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a057d6-a765-7aef-843f-39f50fe0565b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a057d6-a765-7aef-843f-39f50fe0565b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a057d6-a765-7aef-843f-39f50fe0565b" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a057d6-a765-7aef-843f-39f50fe0565b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a057d6-a765-7d8e-8866-7317953188a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a057d6-a765-7aef-843f-39f50fe0565b" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a057d6-a765-7d8e-8866-7317953188a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_01a057d6-a765-70b0-9b09-493054e7b11b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a057d6-a765-7d8e-8866-7317953188a1" xlink:to="loc_us-gaap_SalesRevenueNetMember_01a057d6-a765-70b0-9b09-493054e7b11b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a057d6-a765-7466-b5cd-677a07c3f7ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_01a057d6-a765-7d4d-9058-28a2d25ffffa" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a057d6-a765-7466-b5cd-677a07c3f7ff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a057d6-a765-7466-b5cd-677a07c3f7ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a057d6-a765-7466-b5cd-677a07c3f7ff" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a057d6-a765-7466-b5cd-677a07c3f7ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a057d6-a765-7a92-a8a1-aa41f7de7ef2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a057d6-a765-7466-b5cd-677a07c3f7ff" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a057d6-a765-7a92-a8a1-aa41f7de7ef2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_01a057d6-a765-77df-a9db-f963cd401ce3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a057d6-a765-7a92-a8a1-aa41f7de7ef2" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_01a057d6-a765-77df-a9db-f963cd401ce3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNumberOfAircraftSold_01a057d6-a765-7019-ae5a-1f24dfb9c9be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNumberOfAircraftSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_01a057d6-a765-73ed-8903-0d2230d1f0b3" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNumberOfAircraftSold_01a057d6-a765-7019-ae5a-1f24dfb9c9be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_01a057d6-a765-7dfd-8d3e-3a42da5b945e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_01a057d6-a765-73ed-8903-0d2230d1f0b3" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_01a057d6-a765-7dfd-8d3e-3a42da5b945e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a057d6-a765-791a-988f-6e738fcfb33b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_01a057d6-a765-73ed-8903-0d2230d1f0b3" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a057d6-a765-791a-988f-6e738fcfb33b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesMarketableSecuritiesandLongTermRestrictedInvestmentsandDuefromBrokerDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesMarketableSecuritiesandLongTermRestrictedInvestmentsandDuefromBrokerDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesMarketableSecuritiesandLongTermRestrictedInvestmentsandDuefromBrokerDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_019f6134-5b80-7225-b700-891cbecfd80e" xlink:href="hrbr-20251231.xsd#hrbr_SummaryOfSignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f6134-5b80-7962-ac65-717bae19cec8" xlink:href="hrbr-20251231.xsd#hrbr_SummaryOfSignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_019f6134-5b80-7225-b700-891cbecfd80e" xlink:to="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f6134-5b80-7962-ac65-717bae19cec8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019f6134-5b80-78b8-b05a-7eb48d133d91" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesTable_019f6134-5b80-7962-ac65-717bae19cec8" xlink:to="loc_dei_LegalEntityAxis_019f6134-5b80-78b8-b05a-7eb48d133d91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019f6134-5b80-78b8-b05a-7eb48d133d91_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019f6134-5b80-78b8-b05a-7eb48d133d91" xlink:to="loc_dei_EntityDomain_019f6134-5b80-78b8-b05a-7eb48d133d91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019f6134-5b80-7bd1-a79a-223e766687dc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019f6134-5b80-78b8-b05a-7eb48d133d91" xlink:to="loc_dei_EntityDomain_019f6134-5b80-7bd1-a79a-223e766687dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AirWisconsinMember_019f6134-5b80-7661-a76c-43572af2e08b" xlink:href="hrbr-20251231.xsd#hrbr_AirWisconsinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019f6134-5b80-7bd1-a79a-223e766687dc" xlink:to="loc_hrbr_AirWisconsinMember_019f6134-5b80-7661-a76c-43572af2e08b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_EquitySecuritiesFVNICurrentAndRestrictedInvestmentsNoncurrent_019f6134-5b80-7438-a04c-0aaa0eb93b57" xlink:href="hrbr-20251231.xsd#hrbr_EquitySecuritiesFVNICurrentAndRestrictedInvestmentsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_019f6134-5b80-7225-b700-891cbecfd80e" xlink:to="loc_hrbr_EquitySecuritiesFVNICurrentAndRestrictedInvestmentsNoncurrent_019f6134-5b80-7438-a04c-0aaa0eb93b57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DueFromCorrespondentBrokers_01a0582a-d833-7b03-859d-34200b54e7e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DueFromCorrespondentBrokers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SummaryOfSignificantAccountingPoliciesLineItems_019f6134-5b80-7225-b700-891cbecfd80e" xlink:to="loc_us-gaap_DueFromCorrespondentBrokers_01a0582a-d833-7b03-859d-34200b54e7e8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesSparePartsandSuppliesDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesSparePartsandSuppliesDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesSparePartsandSuppliesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a0c4cd-774c-766a-81d3-00e7bc65b43e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a0c4cd-774c-76eb-a731-24adf38458d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a0c4cd-774c-766a-81d3-00e7bc65b43e" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a0c4cd-774c-76eb-a731-24adf38458d8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeAxis_01a0c4cd-774c-7201-acdd-d8551abee653" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a0c4cd-774c-76eb-a731-24adf38458d8" xlink:to="loc_srt_AircraftTypeAxis_01a0c4cd-774c-7201-acdd-d8551abee653" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeMember_01a0c4cd-774c-7201-acdd-d8551abee653_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_AircraftTypeAxis_01a0c4cd-774c-7201-acdd-d8551abee653" xlink:to="loc_srt_AircraftTypeMember_01a0c4cd-774c-7201-acdd-d8551abee653_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeMember_01a0c4cd-774c-78be-a4c4-251e971e4fc8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_AircraftTypeAxis_01a0c4cd-774c-7201-acdd-d8551abee653" xlink:to="loc_srt_AircraftTypeMember_01a0c4cd-774c-78be-a4c4-251e971e4fc8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_OldFleetTypeMember_01a0c4cd-774c-72dd-913c-e910e6125b70" xlink:href="hrbr-20251231.xsd#hrbr_OldFleetTypeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_AircraftTypeMember_01a0c4cd-774c-78be-a4c4-251e971e4fc8" xlink:to="loc_hrbr_OldFleetTypeMember_01a0c4cd-774c-72dd-913c-e910e6125b70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirlineRelatedInventoryValuationReserves_01a0c4cd-774c-70dc-9a56-e00d62ba4e6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirlineRelatedInventoryValuationReserves"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a0c4cd-774c-766a-81d3-00e7bc65b43e" xlink:to="loc_us-gaap_AirlineRelatedInventoryValuationReserves_01a0c4cd-774c-70dc-9a56-e00d62ba4e6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirlineRelatedInventoryNet_01a0c4cd-774c-7916-a8c0-28d05987d3be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirlineRelatedInventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a0c4cd-774c-766a-81d3-00e7bc65b43e" xlink:to="loc_us-gaap_AirlineRelatedInventoryNet_01a0c4cd-774c-7916-a8c0-28d05987d3be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryAdjustments_019f3773-1571-7f19-96f6-98dce39921a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a0c4cd-774c-766a-81d3-00e7bc65b43e" xlink:to="loc_us-gaap_InventoryAdjustments_019f3773-1571-7f19-96f6-98dce39921a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SparePartsAndSuppliesNetCarryingValue_019f3773-1571-71e9-8791-7233bb711707" xlink:href="hrbr-20251231.xsd#hrbr_SparePartsAndSuppliesNetCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a0c4cd-774c-766a-81d3-00e7bc65b43e" xlink:to="loc_hrbr_SparePartsAndSuppliesNetCarryingValue_019f3773-1571-71e9-8791-7233bb711707" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesScheduleofPropertyandEquipmentUsefulLivesDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesScheduleofPropertyandEquipmentUsefulLivesDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesScheduleofPropertyandEquipmentUsefulLivesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-763d-8d34-d712b11bcd5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019f3773-1571-752e-a83a-8e55e6ac8496" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-763d-8d34-d712b11bcd5d" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019f3773-1571-752e-a83a-8e55e6ac8496" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-72e7-ae2f-7f1ce76e9e51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019f3773-1571-752e-a83a-8e55e6ac8496" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-72e7-ae2f-7f1ce76e9e51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-72e7-ae2f-7f1ce76e9e51_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-72e7-ae2f-7f1ce76e9e51" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-72e7-ae2f-7f1ce76e9e51_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7573-9a07-744cf2900913" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-72e7-ae2f-7f1ce76e9e51" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7573-9a07-744cf2900913" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirTransportationEquipmentMember_019f3773-1571-7354-9277-f0d61f134960" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirTransportationEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7573-9a07-744cf2900913" xlink:to="loc_us-gaap_AirTransportationEquipmentMember_019f3773-1571-7354-9277-f0d61f134960" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_RotablePartsMember_019f3773-1571-7223-bcfd-d470c5f16ec1" xlink:href="hrbr-20251231.xsd#hrbr_RotablePartsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7573-9a07-744cf2900913" xlink:to="loc_hrbr_RotablePartsMember_019f3773-1571-7223-bcfd-d470c5f16ec1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SpareEnginesMember_019f3773-1571-7044-a694-5412bb7e4372" xlink:href="hrbr-20251231.xsd#hrbr_SpareEnginesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7573-9a07-744cf2900913" xlink:to="loc_hrbr_SpareEnginesMember_019f3773-1571-7044-a694-5412bb7e4372" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_GroundEquipmentMember_019f3773-1571-7af7-bfd9-feb926922b79" xlink:href="hrbr-20251231.xsd#hrbr_GroundEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7573-9a07-744cf2900913" xlink:to="loc_hrbr_GroundEquipmentMember_019f3773-1571-7af7-bfd9-feb926922b79" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OfficeEquipmentMember_019f3773-1571-768b-904f-1524c879134e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7573-9a07-744cf2900913" xlink:to="loc_us-gaap_OfficeEquipmentMember_019f3773-1571-768b-904f-1524c879134e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019f3773-1571-77ae-a63e-d8d09b8da159" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7573-9a07-744cf2900913" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019f3773-1571-77ae-a63e-d8d09b8da159" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019f3773-1571-7bc4-9c88-1f75078b1bbc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-763d-8d34-d712b11bcd5d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019f3773-1571-7bc4-9c88-1f75078b1bbc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_ResidualValueOfPropertyPlantAndEquipment_019f3773-1571-7201-9f7a-661d57bae339" xlink:href="hrbr-20251231.xsd#hrbr_ResidualValueOfPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-763d-8d34-d712b11bcd5d" xlink:to="loc_hrbr_ResidualValueOfPropertyPlantAndEquipment_019f3773-1571-7201-9f7a-661d57bae339" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_PercentageOfResidualValueOfPropertyPlantAndEquipment_019f3773-1571-71d2-a71e-02d423ef71cb" xlink:href="hrbr-20251231.xsd#hrbr_PercentageOfResidualValueOfPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-763d-8d34-d712b11bcd5d" xlink:to="loc_hrbr_PercentageOfResidualValueOfPropertyPlantAndEquipment_019f3773-1571-71d2-a71e-02d423ef71cb" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesPropertyandEquipmentDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesPropertyandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesPropertyandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-7bcb-8ce5-1b7b9ff1ce14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019f3773-1571-7091-8959-6acf7247c798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-7bcb-8ce5-1b7b9ff1ce14" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019f3773-1571-7091-8959-6acf7247c798" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-72a1-8e4c-16dafe574111" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019f3773-1571-7091-8959-6acf7247c798" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-72a1-8e4c-16dafe574111" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-72a1-8e4c-16dafe574111_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-72a1-8e4c-16dafe574111" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-72a1-8e4c-16dafe574111_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7241-abee-56f034099c08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-72a1-8e4c-16dafe574111" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7241-abee-56f034099c08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_019f3773-1571-72b5-ad38-924b299fc73a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7241-abee-56f034099c08" xlink:to="loc_us-gaap_ConstructionInProgressMember_019f3773-1571-72b5-ad38-924b299fc73a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019f7d7d-39fb-7bd3-a3b6-80064ea36788" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019f3773-1571-7091-8959-6acf7247c798" xlink:to="loc_srt_CounterpartyNameAxis_019f7d7d-39fb-7bd3-a3b6-80064ea36788" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f7d7d-39fb-7bd3-a3b6-80064ea36788_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019f7d7d-39fb-7bd3-a3b6-80064ea36788" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f7d7d-39fb-7bd3-a3b6-80064ea36788_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f7d7d-39fb-76f3-93b5-fc8ccc972401" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019f7d7d-39fb-7bd3-a3b6-80064ea36788" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f7d7d-39fb-76f3-93b5-fc8ccc972401" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AirWisconsinMember_019f7d7d-39fb-7990-825a-165baebe4e0f" xlink:href="hrbr-20251231.xsd#hrbr_AirWisconsinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f7d7d-39fb-76f3-93b5-fc8ccc972401" xlink:to="loc_hrbr_AirWisconsinMember_019f7d7d-39fb-7990-825a-165baebe4e0f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019f3773-1571-73be-b5b8-0ca98122872c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-7bcb-8ce5-1b7b9ff1ce14" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019f3773-1571-73be-b5b8-0ca98122872c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_NumberOfJetsOwned_019f7d7d-39fb-77de-ac0b-c9005a927493" xlink:href="hrbr-20251231.xsd#hrbr_NumberOfJetsOwned"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-7bcb-8ce5-1b7b9ff1ce14" xlink:to="loc_hrbr_NumberOfJetsOwned_019f7d7d-39fb-77de-ac0b-c9005a927493" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_019f3773-1571-7351-88d3-8e997e3994b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-7bcb-8ce5-1b7b9ff1ce14" xlink:to="loc_us-gaap_Depreciation_019f3773-1571-7351-88d3-8e997e3994b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfAssets1_019f3773-1571-7c95-8f3b-71e22a0a5483" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDispositionOfAssets1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-7bcb-8ce5-1b7b9ff1ce14" xlink:to="loc_us-gaap_GainLossOnDispositionOfAssets1_019f3773-1571-7c95-8f3b-71e22a0a5483" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesScheduleofOriginalCostofCompanysFixedAssetsandAccumulatedDepreciationorAmortizationDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesScheduleofOriginalCostofCompanysFixedAssetsandAccumulatedDepreciationorAmortizationDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesScheduleofOriginalCostofCompanysFixedAssetsandAccumulatedDepreciationorAmortizationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-7dab-b419-03ff64a95704" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019f3773-1571-7ab8-a5e9-d2548e7474d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-7dab-b419-03ff64a95704" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019f3773-1571-7ab8-a5e9-d2548e7474d0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-7baa-a971-f5d3c676b9c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019f3773-1571-7ab8-a5e9-d2548e7474d0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-7baa-a971-f5d3c676b9c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7baa-a971-f5d3c676b9c6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-7baa-a971-f5d3c676b9c6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-7baa-a971-f5d3c676b9c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-79c0-9b32-53ab17bebdb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f3773-1571-7baa-a971-f5d3c676b9c6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-79c0-9b32-53ab17bebdb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_PropertyPlantAndEquipmentExcludingConstructionInProgressMember_019f3773-1571-7617-802e-62ee695cc205" xlink:href="hrbr-20251231.xsd#hrbr_PropertyPlantAndEquipmentExcludingConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f3773-1571-79c0-9b32-53ab17bebdb0" xlink:to="loc_hrbr_PropertyPlantAndEquipmentExcludingConstructionInProgressMember_019f3773-1571-7617-802e-62ee695cc205" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirTransportationEquipmentMember_019f3773-1571-70b8-8713-9935dd922e35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirTransportationEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_PropertyPlantAndEquipmentExcludingConstructionInProgressMember_019f3773-1571-7617-802e-62ee695cc205" xlink:to="loc_us-gaap_AirTransportationEquipmentMember_019f3773-1571-70b8-8713-9935dd922e35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SpareEnginesMember_019f3773-1571-7521-ae54-4d1506fc575b" xlink:href="hrbr-20251231.xsd#hrbr_SpareEnginesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_PropertyPlantAndEquipmentExcludingConstructionInProgressMember_019f3773-1571-7617-802e-62ee695cc205" xlink:to="loc_hrbr_SpareEnginesMember_019f3773-1571-7521-ae54-4d1506fc575b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_RotablePartsMember_019f3773-1571-7a63-a105-777d32857499" xlink:href="hrbr-20251231.xsd#hrbr_RotablePartsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_PropertyPlantAndEquipmentExcludingConstructionInProgressMember_019f3773-1571-7617-802e-62ee695cc205" xlink:to="loc_hrbr_RotablePartsMember_019f3773-1571-7a63-a105-777d32857499" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_GroundEquipmentMember_019f3773-1571-7767-bd3f-19f36677799b" xlink:href="hrbr-20251231.xsd#hrbr_GroundEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_PropertyPlantAndEquipmentExcludingConstructionInProgressMember_019f3773-1571-7617-802e-62ee695cc205" xlink:to="loc_hrbr_GroundEquipmentMember_019f3773-1571-7767-bd3f-19f36677799b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OfficeEquipmentMember_019f3773-1571-7500-bdca-e730c25257ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_PropertyPlantAndEquipmentExcludingConstructionInProgressMember_019f3773-1571-7617-802e-62ee695cc205" xlink:to="loc_us-gaap_OfficeEquipmentMember_019f3773-1571-7500-bdca-e730c25257ea" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019f3773-1571-7364-aebf-33522adec612" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_PropertyPlantAndEquipmentExcludingConstructionInProgressMember_019f3773-1571-7617-802e-62ee695cc205" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019f3773-1571-7364-aebf-33522adec612" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019f3773-1571-7a3e-8bf8-aa1ab1c5e8b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-7dab-b419-03ff64a95704" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019f3773-1571-7a3e-8bf8-aa1ab1c5e8b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_PropertyPlantAndEquipmentBeforeAccumulatedDepreciationDepletionAndAmortizationExcludingConstructionInProgress_019f6123-60e5-761a-8c3e-cbbc6e587467" xlink:href="hrbr-20251231.xsd#hrbr_PropertyPlantAndEquipmentBeforeAccumulatedDepreciationDepletionAndAmortizationExcludingConstructionInProgress"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019f3773-1571-7dab-b419-03ff64a95704" xlink:to="loc_hrbr_PropertyPlantAndEquipmentBeforeAccumulatedDepreciationDepletionAndAmortizationExcludingConstructionInProgress_019f6123-60e5-761a-8c3e-cbbc6e587467" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesScheduleofOtherAssetsDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesScheduleofOtherAssetsDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesScheduleofOtherAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationLineItems_019f3773-1571-7d7a-8277-06ce42f895c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationTable_019f3773-1571-74d1-b2be-d50c0d81aab3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_019f3773-1571-7d7a-8277-06ce42f895c0" xlink:to="loc_us-gaap_IncomeTaxExaminationTable_019f3773-1571-74d1-b2be-d50c0d81aab3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019f3773-1571-76b6-a163-abb4e0334b89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxExaminationTable_019f3773-1571-74d1-b2be-d50c0d81aab3" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019f3773-1571-76b6-a163-abb4e0334b89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019f3773-1571-76b6-a163-abb4e0334b89_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019f3773-1571-76b6-a163-abb4e0334b89" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019f3773-1571-76b6-a163-abb4e0334b89_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019f3773-1571-7b1d-89b7-8c25061fc95f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019f3773-1571-76b6-a163-abb4e0334b89" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019f3773-1571-7b1d-89b7-8c25061fc95f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_019f3773-1571-752c-a4f1-129bf53a2288" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019f3773-1571-7b1d-89b7-8c25061fc95f" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_019f3773-1571-752c-a4f1-129bf53a2288" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_FederalTaxAuthorityMember_019f3773-1571-7929-b2cf-836ce0cee3eb" xlink:href="hrbr-20251231.xsd#hrbr_FederalTaxAuthorityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019f3773-1571-7b1d-89b7-8c25061fc95f" xlink:to="loc_hrbr_FederalTaxAuthorityMember_019f3773-1571-7929-b2cf-836ce0cee3eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodAxis_01a10d12-a5d6-78dd-a07c-508009fc44d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxExaminationTable_019f3773-1571-74d1-b2be-d50c0d81aab3" xlink:to="loc_us-gaap_TaxPeriodAxis_01a10d12-a5d6-78dd-a07c-508009fc44d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_01a10d12-a5d6-78dd-a07c-508009fc44d9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxPeriodAxis_01a10d12-a5d6-78dd-a07c-508009fc44d9" xlink:to="loc_us-gaap_TaxPeriodDomain_01a10d12-a5d6-78dd-a07c-508009fc44d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_01a10d12-a5d6-7ec3-8f0e-46ce6980be97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxPeriodAxis_01a10d12-a5d6-78dd-a07c-508009fc44d9" xlink:to="loc_us-gaap_TaxPeriodDomain_01a10d12-a5d6-7ec3-8f0e-46ce6980be97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxYear2022Member_01a10d12-a5d6-7167-b852-0fb2c227b9b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxYear2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_01a10d12-a5d6-7ec3-8f0e-46ce6980be97" xlink:to="loc_us-gaap_TaxYear2022Member_01a10d12-a5d6-7167-b852-0fb2c227b9b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationLiabilityRefundAdjustmentFromSettlementWithTaxingAuthority_019f3773-1571-78b1-bfd4-8f69628f1f0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationLiabilityRefundAdjustmentFromSettlementWithTaxingAuthority"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_019f3773-1571-7d7a-8277-06ce42f895c0" xlink:to="loc_us-gaap_IncomeTaxExaminationLiabilityRefundAdjustmentFromSettlementWithTaxingAuthority_019f3773-1571-78b1-bfd4-8f69628f1f0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestReceivableNoncurrent_01a109f9-8a3f-7180-816b-3462c62e0a9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestReceivableNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_019f3773-1571-7d7a-8277-06ce42f895c0" xlink:to="loc_us-gaap_InterestReceivableNoncurrent_01a109f9-8a3f-7180-816b-3462c62e0a9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_WorkersCompensationLossFundNoncurrent_019f3773-1571-7311-adc1-782368b6faa3" xlink:href="hrbr-20251231.xsd#hrbr_WorkersCompensationLossFundNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_019f3773-1571-7d7a-8277-06ce42f895c0" xlink:to="loc_hrbr_WorkersCompensationLossFundNoncurrent_019f3773-1571-7311-adc1-782368b6faa3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_LongTermDeposits_019f3773-1571-7b6e-8da3-cdd39e5bf69f" xlink:href="hrbr-20251231.xsd#hrbr_LongTermDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_019f3773-1571-7d7a-8277-06ce42f895c0" xlink:to="loc_hrbr_LongTermDeposits_019f3773-1571-7b6e-8da3-cdd39e5bf69f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsMiscellaneousNoncurrent_019f3773-1571-7c52-bd07-57ea0a6c7566" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsMiscellaneousNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_019f3773-1571-7d7a-8277-06ce42f895c0" xlink:to="loc_us-gaap_OtherAssetsMiscellaneousNoncurrent_019f3773-1571-7c52-bd07-57ea0a6c7566" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesOtherAssetsDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesOtherAssetsDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesOtherAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationLineItems_01a109fe-9eba-7c5e-9423-2796de21b892" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationTable_01a109fe-9eba-7dbf-848d-920355e06cb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_01a109fe-9eba-7c5e-9423-2796de21b892" xlink:to="loc_us-gaap_IncomeTaxExaminationTable_01a109fe-9eba-7dbf-848d-920355e06cb5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodAxis_01a10d12-5cd5-7842-9902-67ab52d8fc80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxExaminationTable_01a109fe-9eba-7dbf-848d-920355e06cb5" xlink:to="loc_us-gaap_TaxPeriodAxis_01a10d12-5cd5-7842-9902-67ab52d8fc80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_01a10d12-5cd5-7842-9902-67ab52d8fc80_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxPeriodAxis_01a10d12-5cd5-7842-9902-67ab52d8fc80" xlink:to="loc_us-gaap_TaxPeriodDomain_01a10d12-5cd5-7842-9902-67ab52d8fc80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_01a10d12-5cd5-7d9f-bb37-f32a5014580c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxPeriodAxis_01a10d12-5cd5-7842-9902-67ab52d8fc80" xlink:to="loc_us-gaap_TaxPeriodDomain_01a10d12-5cd5-7d9f-bb37-f32a5014580c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxYear2022Member_01a10d12-5cd5-7ba8-93e8-2047e1dd38aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxYear2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_01a10d12-5cd5-7d9f-bb37-f32a5014580c" xlink:to="loc_us-gaap_TaxYear2022Member_01a10d12-5cd5-7ba8-93e8-2047e1dd38aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestReceivableNoncurrent_01a109fe-9eba-75f4-bc1b-5469dfab7306" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestReceivableNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_01a109fe-9eba-7c5e-9423-2796de21b892" xlink:to="loc_us-gaap_InterestReceivableNoncurrent_01a109fe-9eba-75f4-bc1b-5469dfab7306" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesInterestandDividendIncomeandIncomeTaxesDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesInterestandDividendIncomeandIncomeTaxesDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesInterestandDividendIncomeandIncomeTaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationLineItems_01a10d11-bb26-7806-b398-cf7db7cd5c31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationTable_01a10d11-bb26-7d39-a176-fe0d8ec84f36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_01a10d11-bb26-7806-b398-cf7db7cd5c31" xlink:to="loc_us-gaap_IncomeTaxExaminationTable_01a10d11-bb26-7d39-a176-fe0d8ec84f36" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodAxis_01a10d11-bb26-7c1b-a39f-a2bc4c48f1fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxExaminationTable_01a10d11-bb26-7d39-a176-fe0d8ec84f36" xlink:to="loc_us-gaap_TaxPeriodAxis_01a10d11-bb26-7c1b-a39f-a2bc4c48f1fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_01a10d11-bb26-7c1b-a39f-a2bc4c48f1fb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxPeriodAxis_01a10d11-bb26-7c1b-a39f-a2bc4c48f1fb" xlink:to="loc_us-gaap_TaxPeriodDomain_01a10d11-bb26-7c1b-a39f-a2bc4c48f1fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_01a10d11-bb26-74fc-b7de-816318c8fec7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxPeriodAxis_01a10d11-bb26-7c1b-a39f-a2bc4c48f1fb" xlink:to="loc_us-gaap_TaxPeriodDomain_01a10d11-bb26-74fc-b7de-816318c8fec7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxYear2022Member_01a10d11-bb26-7514-ab6f-b80962f5a88d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxYear2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_01a10d11-bb26-74fc-b7de-816318c8fec7" xlink:to="loc_us-gaap_TaxYear2022Member_01a10d11-bb26-7514-ab6f-b80962f5a88d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_019f3773-1571-7302-8952-efa56e83f607" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_01a10d11-bb26-7806-b398-cf7db7cd5c31" xlink:to="loc_us-gaap_InvestmentIncomeInterest_019f3773-1571-7302-8952-efa56e83f607" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeDividend_019f3773-1571-73f2-bcc7-55e93589fccf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeDividend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_01a10d11-bb26-7806-b398-cf7db7cd5c31" xlink:to="loc_us-gaap_InvestmentIncomeDividend_019f3773-1571-73f2-bcc7-55e93589fccf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued_019f3773-1571-74a9-aaf4-cfd537e2de59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_01a10d11-bb26-7806-b398-cf7db7cd5c31" xlink:to="loc_us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued_019f3773-1571-74a9-aaf4-cfd537e2de59" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesConcentrationofCreditRiskDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesConcentrationofCreditRiskDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesConcentrationofCreditRiskDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_019f3773-1571-73e3-b229-8cf5a2399798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_019f3773-1571-782e-b1e6-fc968f2b6c72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019f3773-1571-73e3-b229-8cf5a2399798" xlink:to="loc_us-gaap_ConcentrationRiskTable_019f3773-1571-782e-b1e6-fc968f2b6c72" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementAxis_019f3773-1571-7dde-979c-1f4737163434" xlink:href="hrbr-20251231.xsd#hrbr_AgreementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019f3773-1571-782e-b1e6-fc968f2b6c72" xlink:to="loc_hrbr_AgreementAxis_019f3773-1571-7dde-979c-1f4737163434" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementDomain_019f3773-1571-7dde-979c-1f4737163434_default" xlink:href="hrbr-20251231.xsd#hrbr_AgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_hrbr_AgreementAxis_019f3773-1571-7dde-979c-1f4737163434" xlink:to="loc_hrbr_AgreementDomain_019f3773-1571-7dde-979c-1f4737163434_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementDomain_019f3773-1571-7773-8c76-afc4e49f85a7" xlink:href="hrbr-20251231.xsd#hrbr_AgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_hrbr_AgreementAxis_019f3773-1571-7dde-979c-1f4737163434" xlink:to="loc_hrbr_AgreementDomain_019f3773-1571-7773-8c76-afc4e49f85a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AmericanCapacityPurchaseAgreementMember_019f3773-1571-770b-8efc-8b03171a0561" xlink:href="hrbr-20251231.xsd#hrbr_AmericanCapacityPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_AgreementDomain_019f3773-1571-7773-8c76-afc4e49f85a7" xlink:to="loc_hrbr_AmericanCapacityPurchaseAgreementMember_019f3773-1571-770b-8efc-8b03171a0561" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019f3773-1571-7a85-b666-1654a12a3dde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019f3773-1571-782e-b1e6-fc968f2b6c72" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019f3773-1571-7a85-b666-1654a12a3dde" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019f3773-1571-7a85-b666-1654a12a3dde_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019f3773-1571-7a85-b666-1654a12a3dde" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019f3773-1571-7a85-b666-1654a12a3dde_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019f3773-1571-7ecc-996f-ff5e5525143a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019f3773-1571-7a85-b666-1654a12a3dde" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019f3773-1571-7ecc-996f-ff5e5525143a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019f3773-1571-773d-b2c6-4e3bb67fa980" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019f3773-1571-7ecc-996f-ff5e5525143a" xlink:to="loc_us-gaap_SalesRevenueNetMember_019f3773-1571-773d-b2c6-4e3bb67fa980" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_019f3773-1571-7476-b2f5-233a9d14ea92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019f3773-1571-7ecc-996f-ff5e5525143a" xlink:to="loc_us-gaap_AccountsReceivableMember_019f3773-1571-7476-b2f5-233a9d14ea92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019f3773-1571-7249-9d0a-061c5e49cc8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019f3773-1571-782e-b1e6-fc968f2b6c72" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019f3773-1571-7249-9d0a-061c5e49cc8d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019f3773-1571-7249-9d0a-061c5e49cc8d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019f3773-1571-7249-9d0a-061c5e49cc8d" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019f3773-1571-7249-9d0a-061c5e49cc8d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019f3773-1571-788b-971a-5db90ef4ce2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019f3773-1571-7249-9d0a-061c5e49cc8d" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019f3773-1571-788b-971a-5db90ef4ce2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019f3773-1571-7e8d-b100-6716e6781155" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019f3773-1571-788b-971a-5db90ef4ce2d" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019f3773-1571-7e8d-b100-6716e6781155" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019f3773-1571-7462-933e-633083226117" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019f3773-1571-73e3-b229-8cf5a2399798" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019f3773-1571-7462-933e-633083226117" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_019f3773-1571-75dc-a31f-dc1383ae72a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019f3773-1571-73e3-b229-8cf5a2399798" xlink:to="loc_us-gaap_RestrictedCash_019f3773-1571-75dc-a31f-dc1383ae72a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019f3773-1571-7256-a06a-45ff801387aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019f3773-1571-73e3-b229-8cf5a2399798" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019f3773-1571-7256-a06a-45ff801387aa" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesScheduleofClassificationofMarketableSecuritiesAndLongTermInvestmentsDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesScheduleofClassificationofMarketableSecuritiesAndLongTermInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesScheduleofClassificationofMarketableSecuritiesAndLongTermInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019f3773-1571-7b2f-9de7-b01992bf989b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019f3773-1571-731e-8719-027f5b28ab97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019f3773-1571-7b2f-9de7-b01992bf989b" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019f3773-1571-731e-8719-027f5b28ab97" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019f3773-1571-7118-89f9-0d8ddedea8d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019f3773-1571-731e-8719-027f5b28ab97" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019f3773-1571-7118-89f9-0d8ddedea8d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019f3773-1571-7118-89f9-0d8ddedea8d1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019f3773-1571-7118-89f9-0d8ddedea8d1" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019f3773-1571-7118-89f9-0d8ddedea8d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019f3773-1571-7625-9757-364c2b976b0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019f3773-1571-7118-89f9-0d8ddedea8d1" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019f3773-1571-7625-9757-364c2b976b0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExchangeTradedFundsMember_019f3773-1571-7748-a7c7-bc1d489ceaf7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExchangeTradedFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019f3773-1571-7625-9757-364c2b976b0d" xlink:to="loc_us-gaap_ExchangeTradedFundsMember_019f3773-1571-7748-a7c7-bc1d489ceaf7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MutualFundMember_019f6112-1d71-70fb-aa81-227d3d50017a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MutualFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019f3773-1571-7625-9757-364c2b976b0d" xlink:to="loc_us-gaap_MutualFundMember_019f6112-1d71-70fb-aa81-227d3d50017a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BondsMember_019f6114-4fb0-7ed0-8433-d439cce7c591" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019f3773-1571-7625-9757-364c2b976b0d" xlink:to="loc_us-gaap_BondsMember_019f6114-4fb0-7ed0-8433-d439cce7c591" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_RestrictedShortTermInvestmentsMutualFundsMember_01a07c28-7590-7e77-946f-556dda838338" xlink:href="hrbr-20251231.xsd#hrbr_RestrictedShortTermInvestmentsMutualFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019f3773-1571-7625-9757-364c2b976b0d" xlink:to="loc_hrbr_RestrictedShortTermInvestmentsMutualFundsMember_01a07c28-7590-7e77-946f-556dda838338" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_RestrictedLongTermInvestmentsMutualFundsMember_019f3773-1571-7de4-992f-c1e8ce88e9e7" xlink:href="hrbr-20251231.xsd#hrbr_RestrictedLongTermInvestmentsMutualFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019f3773-1571-7625-9757-364c2b976b0d" xlink:to="loc_hrbr_RestrictedLongTermInvestmentsMutualFundsMember_019f3773-1571-7de4-992f-c1e8ce88e9e7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019f3773-1571-7f0d-9f38-d6df7424b238" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019f3773-1571-731e-8719-027f5b28ab97" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019f3773-1571-7f0d-9f38-d6df7424b238" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019f3773-1571-7f0d-9f38-d6df7424b238_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019f3773-1571-7f0d-9f38-d6df7424b238" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019f3773-1571-7f0d-9f38-d6df7424b238_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019f3773-1571-7000-9876-9a090492fe49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019f3773-1571-7f0d-9f38-d6df7424b238" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019f3773-1571-7000-9876-9a090492fe49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019f3773-1571-785e-b13f-5c9a9172bb47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019f3773-1571-7000-9876-9a090492fe49" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019f3773-1571-785e-b13f-5c9a9172bb47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019f3773-1571-7be1-a566-feb08482f005" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019f3773-1571-7000-9876-9a090492fe49" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019f3773-1571-7be1-a566-feb08482f005" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019f3773-1571-768e-b826-3b9307f0a417" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019f3773-1571-7000-9876-9a090492fe49" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019f3773-1571-768e-b826-3b9307f0a417" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019f6111-323d-7f27-9c50-625d7692bf80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019f3773-1571-7b2f-9de7-b01992bf989b" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019f6111-323d-7f27-9c50-625d7692bf80" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_LongTermInvestmentsFairValueDisclosure_019f6112-bd67-75fd-8d64-2a2ff99d08a3" xlink:href="hrbr-20251231.xsd#hrbr_LongTermInvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019f3773-1571-7b2f-9de7-b01992bf989b" xlink:to="loc_hrbr_LongTermInvestmentsFairValueDisclosure_019f6112-bd67-75fd-8d64-2a2ff99d08a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_ShortTermInvestmentsFairValueDisclosure_01a07c27-ada7-768e-b380-215fe8a542be" xlink:href="hrbr-20251231.xsd#hrbr_ShortTermInvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019f3773-1571-7b2f-9de7-b01992bf989b" xlink:to="loc_hrbr_ShortTermInvestmentsFairValueDisclosure_01a07c27-ada7-768e-b380-215fe8a542be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019f3773-1571-73c1-8720-6f3c2106de98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019f3773-1571-7b2f-9de7-b01992bf989b" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019f3773-1571-73c1-8720-6f3c2106de98" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SummaryofSignificantAccountingPoliciesReclassificationsDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SummaryofSignificantAccountingPoliciesReclassificationsDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SummaryofSignificantAccountingPoliciesReclassificationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationLineItems_019f3773-1571-772f-82ec-ebff3cfb3a4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTable_019f3773-1571-75d0-9421-d2f5a1d13c43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReclassificationLineItems_019f3773-1571-772f-82ec-ebff3cfb3a4d" xlink:to="loc_us-gaap_ReclassificationTable_019f3773-1571-75d0-9421-d2f5a1d13c43" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_019f3773-1571-7412-940b-e442e98f73ed" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationTable_019f3773-1571-75d0-9421-d2f5a1d13c43" xlink:to="loc_srt_RestatementAxis_019f3773-1571-7412-940b-e442e98f73ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_019f3773-1571-7412-940b-e442e98f73ed_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_019f3773-1571-7412-940b-e442e98f73ed" xlink:to="loc_srt_RestatementDomain_019f3773-1571-7412-940b-e442e98f73ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_019f3773-1571-7fb4-9e59-9f1073cc5170" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_019f3773-1571-7412-940b-e442e98f73ed" xlink:to="loc_srt_RestatementDomain_019f3773-1571-7fb4-9e59-9f1073cc5170" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_01a0c20d-cef7-776a-bc69-ce02f0be55c9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_019f3773-1571-7fb4-9e59-9f1073cc5170" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_01a0c20d-cef7-776a-bc69-ce02f0be55c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAdjustmentMember_01a0c482-8530-7872-a8da-8887a7fe9df1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_019f3773-1571-7fb4-9e59-9f1073cc5170" xlink:to="loc_srt_RestatementAdjustmentMember_01a0c482-8530-7872-a8da-8887a7fe9df1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirlineCapacityPurchaseArrangements_01a0c482-aec7-7fa2-976b-1ed8406cf8bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirlineCapacityPurchaseArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationLineItems_019f3773-1571-772f-82ec-ebff3cfb3a4d" xlink:to="loc_us-gaap_AirlineCapacityPurchaseArrangements_01a0c482-aec7-7fa2-976b-1ed8406cf8bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfOtherAssets_01a0c20d-cef7-7cc7-9dbd-eb89a0533be1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationLineItems_019f3773-1571-772f-82ec-ebff3cfb3a4d" xlink:to="loc_us-gaap_GainLossOnSaleOfOtherAssets_01a0c20d-cef7-7cc7-9dbd-eb89a0533be1" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/CapacityPurchaseAgreementwithAmericanDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#CapacityPurchaseAgreementwithAmericanDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/CapacityPurchaseAgreementwithAmericanDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TypesOfCommercialAircraftLineItems_019f3773-1571-774e-aa18-60a5f14ae616" xlink:href="hrbr-20251231.xsd#hrbr_TypesOfCommercialAircraftLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypesOfCommercialAircraftTable_019f3773-1571-7041-9a55-c6673392ca68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypesOfCommercialAircraftTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_hrbr_TypesOfCommercialAircraftLineItems_019f3773-1571-774e-aa18-60a5f14ae616" xlink:to="loc_us-gaap_TypesOfCommercialAircraftTable_019f3773-1571-7041-9a55-c6673392ca68" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementAxis_019f3773-1571-7bf1-a0fc-e5bb10623064" xlink:href="hrbr-20251231.xsd#hrbr_AgreementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TypesOfCommercialAircraftTable_019f3773-1571-7041-9a55-c6673392ca68" xlink:to="loc_hrbr_AgreementAxis_019f3773-1571-7bf1-a0fc-e5bb10623064" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementDomain_019f3773-1571-7bf1-a0fc-e5bb10623064_default" xlink:href="hrbr-20251231.xsd#hrbr_AgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_hrbr_AgreementAxis_019f3773-1571-7bf1-a0fc-e5bb10623064" xlink:to="loc_hrbr_AgreementDomain_019f3773-1571-7bf1-a0fc-e5bb10623064_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AgreementDomain_019f3773-1571-7025-92b0-aa501c780b32" xlink:href="hrbr-20251231.xsd#hrbr_AgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_hrbr_AgreementAxis_019f3773-1571-7bf1-a0fc-e5bb10623064" xlink:to="loc_hrbr_AgreementDomain_019f3773-1571-7025-92b0-aa501c780b32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AmericanCapacityPurchaseAgreementMember_019f3773-1571-7d21-82b4-33047894a4c7" xlink:href="hrbr-20251231.xsd#hrbr_AmericanCapacityPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_AgreementDomain_019f3773-1571-7025-92b0-aa501c780b32" xlink:to="loc_hrbr_AmericanCapacityPurchaseAgreementMember_019f3773-1571-7d21-82b4-33047894a4c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019f3773-1571-7236-8fbe-232ffd99d60e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TypesOfCommercialAircraftTable_019f3773-1571-7041-9a55-c6673392ca68" xlink:to="loc_srt_CounterpartyNameAxis_019f3773-1571-7236-8fbe-232ffd99d60e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1571-7236-8fbe-232ffd99d60e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019f3773-1571-7236-8fbe-232ffd99d60e" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1571-7236-8fbe-232ffd99d60e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1571-785c-a0c2-2967244592d6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019f3773-1571-7236-8fbe-232ffd99d60e" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1571-785c-a0c2-2967244592d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AirWisconsinMember_019f3773-1571-7d4b-89f3-05fab8a2b27c" xlink:href="hrbr-20251231.xsd#hrbr_AirWisconsinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1571-785c-a0c2-2967244592d6" xlink:to="loc_hrbr_AirWisconsinMember_019f3773-1571-7d4b-89f3-05fab8a2b27c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019f3773-1571-73c5-90eb-db2dacd59290" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TypesOfCommercialAircraftTable_019f3773-1571-7041-9a55-c6673392ca68" xlink:to="loc_dei_LegalEntityAxis_019f3773-1571-73c5-90eb-db2dacd59290" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019f3773-1571-73c5-90eb-db2dacd59290_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019f3773-1571-73c5-90eb-db2dacd59290" xlink:to="loc_dei_EntityDomain_019f3773-1571-73c5-90eb-db2dacd59290_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019f3773-1571-7f1f-ae58-839e1bbc67d5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019f3773-1571-73c5-90eb-db2dacd59290" xlink:to="loc_dei_EntityDomain_019f3773-1571-7f1f-ae58-839e1bbc67d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AmericanAirlinesIncMember_019f3773-1571-7988-ac6c-a9b65b2771df" xlink:href="hrbr-20251231.xsd#hrbr_AmericanAirlinesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019f3773-1571-7f1f-ae58-839e1bbc67d5" xlink:to="loc_hrbr_AmericanAirlinesIncMember_019f3773-1571-7988-ac6c-a9b65b2771df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeAxis_019f3773-1571-78f6-aa18-3afef2b83d63" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TypesOfCommercialAircraftTable_019f3773-1571-7041-9a55-c6673392ca68" xlink:to="loc_srt_AircraftTypeAxis_019f3773-1571-78f6-aa18-3afef2b83d63" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeMember_019f3773-1571-78f6-aa18-3afef2b83d63_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_AircraftTypeAxis_019f3773-1571-78f6-aa18-3afef2b83d63" xlink:to="loc_srt_AircraftTypeMember_019f3773-1571-78f6-aa18-3afef2b83d63_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeMember_019f3773-1571-7e5b-846a-9a91d4c535d2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_AircraftTypeAxis_019f3773-1571-78f6-aa18-3afef2b83d63" xlink:to="loc_srt_AircraftTypeMember_019f3773-1571-7e5b-846a-9a91d4c535d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CRJ200Member_019f3773-1571-76a7-936e-3bcea25e4a13" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CRJ200Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_AircraftTypeMember_019f3773-1571-7e5b-846a-9a91d4c535d2" xlink:to="loc_srt_CRJ200Member_019f3773-1571-76a7-936e-3bcea25e4a13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfAircraftOperated_019f3773-1571-7649-ae53-87a473014e89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfAircraftOperated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_TypesOfCommercialAircraftLineItems_019f3773-1571-774e-aa18-60a5f14ae616" xlink:to="loc_us-gaap_NumberOfAircraftOperated_019f3773-1571-7649-ae53-87a473014e89" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/IncomeTaxesAdditionalInformationDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#IncomeTaxesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/IncomeTaxesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:href="hrbr-20251231.xsd#hrbr_IncomeTaxDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_IncomeTaxDisclosureTable_019f3773-1571-7b83-afd7-aaf7b1592a2a" xlink:href="hrbr-20251231.xsd#hrbr_IncomeTaxDisclosureTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_hrbr_IncomeTaxDisclosureTable_019f3773-1571-7b83-afd7-aaf7b1592a2a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_01a080c8-3461-79ab-bb3c-310733cb8884" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_IncomeTaxDisclosureTable_019f3773-1571-7b83-afd7-aaf7b1592a2a" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_01a080c8-3461-79ab-bb3c-310733cb8884" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_01a080c8-3461-79ab-bb3c-310733cb8884_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_01a080c8-3461-79ab-bb3c-310733cb8884" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_01a080c8-3461-79ab-bb3c-310733cb8884_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_01a080c8-3461-7035-a97d-fbf4fdb3d690" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_01a080c8-3461-79ab-bb3c-310733cb8884" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_01a080c8-3461-7035-a97d-fbf4fdb3d690" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_01a080c8-3461-7ec1-8b3d-e9394149363d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_01a080c8-3461-7035-a97d-fbf4fdb3d690" xlink:to="loc_us-gaap_DomesticCountryMember_01a080c8-3461-7ec1-8b3d-e9394149363d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_01a080c8-3461-740a-b631-a41ca1d45da8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_01a080c8-3461-7035-a97d-fbf4fdb3d690" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_01a080c8-3461-740a-b631-a41ca1d45da8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodAxis_01a080c8-6408-74cc-bac2-e495b0fa4c59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_hrbr_IncomeTaxDisclosureTable_019f3773-1571-7b83-afd7-aaf7b1592a2a" xlink:to="loc_us-gaap_TaxPeriodAxis_01a080c8-6408-74cc-bac2-e495b0fa4c59" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_01a080c8-6408-74cc-bac2-e495b0fa4c59_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxPeriodAxis_01a080c8-6408-74cc-bac2-e495b0fa4c59" xlink:to="loc_us-gaap_TaxPeriodDomain_01a080c8-6408-74cc-bac2-e495b0fa4c59_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_01a080c8-6408-757b-988b-3703baa4adb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxPeriodAxis_01a080c8-6408-74cc-bac2-e495b0fa4c59" xlink:to="loc_us-gaap_TaxPeriodDomain_01a080c8-6408-757b-988b-3703baa4adb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TaxYear2021And2022Member_01a080c8-6408-7f7d-ab84-761de92f535a" xlink:href="hrbr-20251231.xsd#hrbr_TaxYear2021And2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_01a080c8-6408-757b-988b-3703baa4adb8" xlink:to="loc_hrbr_TaxYear2021And2022Member_01a080c8-6408-7f7d-ab84-761de92f535a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxYear2021Member_01a080c8-6408-7341-88fc-248a82009ad5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxYear2021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_TaxYear2021And2022Member_01a080c8-6408-7f7d-ab84-761de92f535a" xlink:to="loc_us-gaap_TaxYear2021Member_01a080c8-6408-7341-88fc-248a82009ad5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxYear2022Member_01a080c8-6408-72c6-86d2-67703b77d30c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxYear2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_TaxYear2021And2022Member_01a080c8-6408-7f7d-ab84-761de92f535a" xlink:to="loc_us-gaap_TaxYear2022Member_01a080c8-6408-72c6-86d2-67703b77d30c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_01a080c7-cf79-7e0b-abf2-fff5df7b1c43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_01a080c7-cf79-7e0b-abf2-fff5df7b1c43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a080c7-ef18-7967-8980-ea09bad14da9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a080c7-ef18-7967-8980-ea09bad14da9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_DeferredTaxAssetsValuationAllowanceOrdinary_01a080c8-15c7-77e1-ad13-95a8dcae5bc3" xlink:href="hrbr-20251231.xsd#hrbr_DeferredTaxAssetsValuationAllowanceOrdinary"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_hrbr_DeferredTaxAssetsValuationAllowanceOrdinary_01a080c8-15c7-77e1-ad13-95a8dcae5bc3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_01a080c8-3461-76a2-a184-2834887b6c0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLossCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_us-gaap_OperatingLossCarryforwards_01a080c8-3461-76a2-a184-2834887b6c0c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlementsStateAndLocal_01a080da-7428-775a-b436-a543669e10b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlementsStateAndLocal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlementsStateAndLocal_01a080da-7428-775a-b436-a543669e10b9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReceivable_01a080c8-6408-7dbe-a54e-71643f90940f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_us-gaap_IncomeTaxReceivable_01a080c8-6408-7dbe-a54e-71643f90940f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIncomeTaxRefunds_01a080c8-6408-761f-ac92-fa40bf51f558" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIncomeTaxRefunds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_us-gaap_ProceedsFromIncomeTaxRefunds_01a080c8-6408-761f-ac92-fa40bf51f558" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivablesNetCurrent_01a080c8-6408-79e4-8a1a-6abd32f52b47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReceivablesNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_us-gaap_ReceivablesNetCurrent_01a080c8-6408-79e4-8a1a-6abd32f52b47" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_01a080c8-6408-73ec-9fcc-7d8eaef18eec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_01a080c8-6408-73ec-9fcc-7d8eaef18eec" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic_01a080c8-6408-7658-bdb3-d3cf0f774935" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic_01a080c8-6408-7658-bdb3-d3cf0f774935" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_IncomeLossFromContinuingOperationsBeforeIncomeTaxesStateAndLocal_01a080c8-6408-7de3-85d9-55fad582bcd7" xlink:href="hrbr-20251231.xsd#hrbr_IncomeLossFromContinuingOperationsBeforeIncomeTaxesStateAndLocal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_hrbr_IncomeLossFromContinuingOperationsBeforeIncomeTaxesStateAndLocal_01a080c8-6408-7de3-85d9-55fad582bcd7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense_01a10a11-aa68-7d88-bb54-d1e585baa3a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_IncomeTaxDisclosureLineItems_01a080c7-cf79-7020-9a16-a8bb56fb7f1e" xlink:to="loc_us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense_01a10a11-aa68-7d88-bb54-d1e585baa3a1" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/IncomeTaxesScheduleofIncomeTaxesPaidNetofRefundsDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#IncomeTaxesScheduleofIncomeTaxesPaidNetofRefundsDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/IncomeTaxesScheduleofIncomeTaxesPaidNetofRefundsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_01a080ae-162e-7032-b02a-90546051bfae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_01a080ae-162e-7a96-b2c5-ee3418b37c87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxPaidByIndividualJurisdictionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_01a080ae-162e-7032-b02a-90546051bfae" xlink:to="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_01a080ae-162e-7a96-b2c5-ee3418b37c87" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_01a080ae-162e-73b8-a437-5829adf6c7c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_01a080ae-162e-7a96-b2c5-ee3418b37c87" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_01a080ae-162e-73b8-a437-5829adf6c7c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_01a080ae-162e-73b8-a437-5829adf6c7c7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_01a080ae-162e-73b8-a437-5829adf6c7c7" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_01a080ae-162e-73b8-a437-5829adf6c7c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_01a080ae-162e-76b2-98ba-e5d202f1df3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_01a080ae-162e-73b8-a437-5829adf6c7c7" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_01a080ae-162e-76b2-98ba-e5d202f1df3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_01a080ae-162e-76b2-98ba-e5d202f1df3e" xlink:to="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_PA_01a080b1-5fa4-7bdd-9579-c34fe62fc0c2" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_PA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:to="loc_stpr_PA_01a080b1-5fa4-7bdd-9579-c34fe62fc0c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_WI_01a080b1-5fa4-7ba9-95cd-6cafed970c3e" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_WI"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:to="loc_stpr_WI_01a080b1-5fa4-7ba9-95cd-6cafed970c3e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_MI_01a080b1-5fa4-7b08-87db-430a2eaa8083" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_MI"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:to="loc_stpr_MI_01a080b1-5fa4-7b08-87db-430a2eaa8083" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_NY_01a080b1-5fa4-7ab3-ba71-0042c3c77d10" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_NY"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:to="loc_stpr_NY_01a080b1-5fa4-7ab3-ba71-0042c3c77d10" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_SC_01a080b1-5fa4-72bc-a60f-15ffb536e730" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_SC"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:to="loc_stpr_SC_01a080b1-5fa4-72bc-a60f-15ffb536e730" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_IL_01a080b1-5fa4-74da-a64e-e6c25e4171fb" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_IL"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:to="loc_stpr_IL_01a080b1-5fa4-74da-a64e-e6c25e4171fb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_ME_01a080b1-5fa4-7c47-9b1f-d3806bf52cdb" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_ME"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:to="loc_stpr_ME_01a080b1-5fa4-7c47-9b1f-d3806bf52cdb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_PhiladelphiaMember_01a080b1-5fa4-754a-b276-9aa16349bccf" xlink:href="hrbr-20251231.xsd#hrbr_PhiladelphiaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:to="loc_hrbr_PhiladelphiaMember_01a080b1-5fa4-754a-b276-9aa16349bccf" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalTaxJurisdictionOtherMember_01a080b1-5fa4-7966-acd8-f611471a9b1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StateAndLocalTaxJurisdictionOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticTaxJurisdictionFederalStateAndLocalMember_01a080b2-c641-7e5f-a5e1-a49e6b844254" xlink:to="loc_us-gaap_StateAndLocalTaxJurisdictionOtherMember_01a080b1-5fa4-7966-acd8-f611471a9b1f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidFederalAfterRefundReceived_01a080ae-162e-7a02-a58a-282e958a1aa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxPaidFederalAfterRefundReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_01a080ae-162e-7032-b02a-90546051bfae" xlink:to="loc_us-gaap_IncomeTaxPaidFederalAfterRefundReceived_01a080ae-162e-7a02-a58a-282e958a1aa1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived_01a080ae-162e-7745-ad65-fd5fc46365bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_01a080ae-162e-7032-b02a-90546051bfae" xlink:to="loc_us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived_01a080ae-162e-7745-ad65-fd5fc46365bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_01a080ae-162e-7b55-a16f-12f3e2144363" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_01a080ae-162e-7032-b02a-90546051bfae" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_01a080ae-162e-7b55-a16f-12f3e2144363" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/LongtermPromissoryNoteDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#LongtermPromissoryNoteDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/LongtermPromissoryNoteDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtLineItems_019f3773-1571-758d-8716-d20481df12b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtinguishmentOfDebtLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfExtinguishmentOfDebtTable_019f3773-1571-7bfc-8ff6-6c53e2f866e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfExtinguishmentOfDebtTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ExtinguishmentOfDebtLineItems_019f3773-1571-758d-8716-d20481df12b5" xlink:to="loc_us-gaap_ScheduleOfExtinguishmentOfDebtTable_019f3773-1571-7bfc-8ff6-6c53e2f866e4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_019f3773-1571-7a5b-b2ab-372b622a93cb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfExtinguishmentOfDebtTable_019f3773-1571-7bfc-8ff6-6c53e2f866e4" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_019f3773-1571-7a5b-b2ab-372b622a93cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_019f3773-1571-7a5b-b2ab-372b622a93cb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_019f3773-1571-7a5b-b2ab-372b622a93cb" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_019f3773-1571-7a5b-b2ab-372b622a93cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_019f3773-1571-7b9f-a0f6-213416db0311" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_019f3773-1571-7a5b-b2ab-372b622a93cb" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_019f3773-1571-7b9f-a0f6-213416db0311" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_HangarMember_019f3773-1571-7750-a2aa-07b62cdbe6ce" xlink:href="hrbr-20251231.xsd#hrbr_HangarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_019f3773-1571-7b9f-a0f6-213416db0311" xlink:to="loc_hrbr_HangarMember_019f3773-1571-7750-a2aa-07b62cdbe6ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019f3773-1571-715f-b3fb-606af8d7e557" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfExtinguishmentOfDebtTable_019f3773-1571-7bfc-8ff6-6c53e2f866e4" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019f3773-1571-715f-b3fb-606af8d7e557" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019f3773-1571-715f-b3fb-606af8d7e557_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019f3773-1571-715f-b3fb-606af8d7e557" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019f3773-1571-715f-b3fb-606af8d7e557_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019f3773-1571-7a53-b845-ddc1c4968d43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019f3773-1571-715f-b3fb-606af8d7e557" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019f3773-1571-7a53-b845-ddc1c4968d43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019f3773-1571-7c25-912d-a54623377161" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019f3773-1571-7a53-b845-ddc1c4968d43" xlink:to="loc_us-gaap_SeniorNotesMember_019f3773-1571-7c25-912d-a54623377161" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019f3773-1571-79ae-bfb6-2365e435e5cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtLineItems_019f3773-1571-758d-8716-d20481df12b5" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019f3773-1571-79ae-bfb6-2365e435e5cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019f3773-1571-786f-83e0-8fb2ad90652f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtLineItems_019f3773-1571-758d-8716-d20481df12b5" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019f3773-1571-786f-83e0-8fb2ad90652f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/LeaseObligationsAdditionalInformationDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#LeaseObligationsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/LeaseObligationsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f3773-1571-783a-a491-86c04bc0a566" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019f3773-1571-71c2-b37b-af7a0bc619cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f3773-1571-783a-a491-86c04bc0a566" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019f3773-1571-71c2-b37b-af7a0bc619cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019f3773-1571-75f7-9100-38e0f047efc5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019f3773-1571-71c2-b37b-af7a0bc619cd" xlink:to="loc_srt_RangeAxis_019f3773-1571-75f7-9100-38e0f047efc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019f3773-1571-75f7-9100-38e0f047efc5_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019f3773-1571-75f7-9100-38e0f047efc5" xlink:to="loc_srt_RangeMember_019f3773-1571-75f7-9100-38e0f047efc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019f3773-1571-79eb-87b1-cd47c20fb5c7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019f3773-1571-75f7-9100-38e0f047efc5" xlink:to="loc_srt_RangeMember_019f3773-1571-79eb-87b1-cd47c20fb5c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019f3773-1571-7a1b-907d-6befe3916f18" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019f3773-1571-79eb-87b1-cd47c20fb5c7" xlink:to="loc_srt_MinimumMember_019f3773-1571-7a1b-907d-6befe3916f18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019f3773-1571-76bc-b52f-bd91241b2e52" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019f3773-1571-79eb-87b1-cd47c20fb5c7" xlink:to="loc_srt_MaximumMember_019f3773-1571-76bc-b52f-bd91241b2e52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019f3773-1571-70e4-b88c-2bd1b67025ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f3773-1571-783a-a491-86c04bc0a566" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019f3773-1571-70e4-b88c-2bd1b67025ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019f3773-1571-7902-b93b-5d8fbff3b9ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f3773-1571-783a-a491-86c04bc0a566" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019f3773-1571-7902-b93b-5d8fbff3b9ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_019f3773-1571-7432-9b9b-2fcdb44ee6bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f3773-1571-783a-a491-86c04bc0a566" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_019f3773-1571-7432-9b9b-2fcdb44ee6bb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019f3773-1571-7f94-bb9a-6cd23501b0ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f3773-1571-783a-a491-86c04bc0a566" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019f3773-1571-7f94-bb9a-6cd23501b0ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_019f3773-1571-79e7-80d1-00e8a4c31f06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f3773-1571-783a-a491-86c04bc0a566" xlink:to="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_019f3773-1571-79e7-80d1-00e8a4c31f06" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasePayments_019f3773-1571-7492-913a-db02b3f9d608" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeasePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f3773-1571-783a-a491-86c04bc0a566" xlink:to="loc_us-gaap_OperatingLeasePayments_019f3773-1571-7492-913a-db02b3f9d608" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseTermOfContract_019f3773-1571-7c49-a047-2bca04e9b9a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f3773-1571-783a-a491-86c04bc0a566" xlink:to="loc_us-gaap_LesseeOperatingLeaseTermOfContract_019f3773-1571-7c49-a047-2bca04e9b9a6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_OperatingLeasesRentExpense_019f3773-1571-7201-8235-294341a83dd3" xlink:href="hrbr-20251231.xsd#hrbr_OperatingLeasesRentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f3773-1571-783a-a491-86c04bc0a566" xlink:to="loc_hrbr_OperatingLeasesRentExpense_019f3773-1571-7201-8235-294341a83dd3" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/CommitmentsandContingenciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_019f3773-1571-74c7-933a-c8fdc5ef6b7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsTable_019f3773-1571-7d8b-a58b-9d3348025115" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019f3773-1571-74c7-933a-c8fdc5ef6b7e" xlink:to="loc_us-gaap_OtherCommitmentsTable_019f3773-1571-7d8b-a58b-9d3348025115" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_019f3773-1571-79bb-b512-11325e9226c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_019f3773-1571-7d8b-a58b-9d3348025115" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_019f3773-1571-79bb-b512-11325e9226c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019f3773-1571-79bb-b512-11325e9226c2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019f3773-1571-79bb-b512-11325e9226c2" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019f3773-1571-79bb-b512-11325e9226c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019f3773-1571-743a-8db9-efb277c006ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019f3773-1571-79bb-b512-11325e9226c2" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019f3773-1571-743a-8db9-efb277c006ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_019f3773-1571-798f-95b7-543143c71ee2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019f3773-1571-743a-8db9-efb277c006ab" xlink:to="loc_us-gaap_LetterOfCreditMember_019f3773-1571-798f-95b7-543143c71ee2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f3773-1571-70d7-9626-64ea76607be9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_019f3773-1571-7d8b-a58b-9d3348025115" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f3773-1571-70d7-9626-64ea76607be9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019f3773-1571-70d7-9626-64ea76607be9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f3773-1571-70d7-9626-64ea76607be9" xlink:to="loc_us-gaap_RelatedPartyDomain_019f3773-1571-70d7-9626-64ea76607be9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019f3773-1571-7abe-80cc-8c993b5cb321" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f3773-1571-70d7-9626-64ea76607be9" xlink:to="loc_us-gaap_RelatedPartyDomain_019f3773-1571-7abe-80cc-8c993b5cb321" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019f3773-1571-7974-a37d-e5137a7b7f02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019f3773-1571-7abe-80cc-8c993b5cb321" xlink:to="loc_us-gaap_RelatedPartyMember_019f3773-1571-7974-a37d-e5137a7b7f02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019f3773-1571-7142-b4a1-d7848e0e2c62" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_019f3773-1571-7d8b-a58b-9d3348025115" xlink:to="loc_srt_CounterpartyNameAxis_019f3773-1571-7142-b4a1-d7848e0e2c62" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1571-7142-b4a1-d7848e0e2c62_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019f3773-1571-7142-b4a1-d7848e0e2c62" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1571-7142-b4a1-d7848e0e2c62_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1571-731c-b7f7-bf3c4400942d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019f3773-1571-7142-b4a1-d7848e0e2c62" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1571-731c-b7f7-bf3c4400942d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AirWisconsinMember_019f3773-1571-736f-9896-5799b21acf5c" xlink:href="hrbr-20251231.xsd#hrbr_AirWisconsinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1571-731c-b7f7-bf3c4400942d" xlink:to="loc_hrbr_AirWisconsinMember_019f3773-1571-736f-9896-5799b21acf5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SchemeAxis_019ffe88-4b97-743c-a53e-82a668f7df86" xlink:href="hrbr-20251231.xsd#hrbr_SchemeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_019f3773-1571-7d8b-a58b-9d3348025115" xlink:to="loc_hrbr_SchemeAxis_019ffe88-4b97-743c-a53e-82a668f7df86" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SchemeDomain_019ffe88-4b97-743c-a53e-82a668f7df86_default" xlink:href="hrbr-20251231.xsd#hrbr_SchemeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_hrbr_SchemeAxis_019ffe88-4b97-743c-a53e-82a668f7df86" xlink:to="loc_hrbr_SchemeDomain_019ffe88-4b97-743c-a53e-82a668f7df86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SchemeDomain_019ffe88-4b97-702b-80cd-2e6bfa19d431" xlink:href="hrbr-20251231.xsd#hrbr_SchemeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_hrbr_SchemeAxis_019ffe88-4b97-743c-a53e-82a668f7df86" xlink:to="loc_hrbr_SchemeDomain_019ffe88-4b97-702b-80cd-2e6bfa19d431" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TreasuryPayrollAndSupportProgrammeMember_019ffe88-4b97-7792-83bb-b7a4a30d7d26" xlink:href="hrbr-20251231.xsd#hrbr_TreasuryPayrollAndSupportProgrammeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_hrbr_SchemeDomain_019ffe88-4b97-702b-80cd-2e6bfa19d431" xlink:to="loc_hrbr_TreasuryPayrollAndSupportProgrammeMember_019ffe88-4b97-7792-83bb-b7a4a30d7d26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_01a080e4-becb-7ab4-9a7c-f8b90b484bb3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_019f3773-1571-7d8b-a58b-9d3348025115" xlink:to="loc_srt_LitigationCaseAxis_01a080e4-becb-7ab4-9a7c-f8b90b484bb3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_01a080e4-becb-7ab4-9a7c-f8b90b484bb3_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_01a080e4-becb-7ab4-9a7c-f8b90b484bb3" xlink:to="loc_srt_LitigationCaseTypeDomain_01a080e4-becb-7ab4-9a7c-f8b90b484bb3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_01a080e4-becb-7b28-b664-2def53cf3cd2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_01a080e4-becb-7ab4-9a7c-f8b90b484bb3" xlink:to="loc_srt_LitigationCaseTypeDomain_01a080e4-becb-7b28-b664-2def53cf3cd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_ToftV.HarborDiversifiedInc.Member_01a080e4-becb-7daa-a3fb-fd6ed005cd66" xlink:href="hrbr-20251231.xsd#hrbr_ToftV.HarborDiversifiedInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_01a080e4-becb-7b28-b664-2def53cf3cd2" xlink:to="loc_hrbr_ToftV.HarborDiversifiedInc.Member_01a080e4-becb-7daa-a3fb-fd6ed005cd66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_01a11bcd-4c6d-76c8-a7c2-608209951b24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_019f3773-1571-7d8b-a58b-9d3348025115" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_01a11bcd-4c6d-76c8-a7c2-608209951b24" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a11bcd-4c6d-76c8-a7c2-608209951b24_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a11bcd-4c6d-76c8-a7c2-608209951b24" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a11bcd-4c6d-76c8-a7c2-608209951b24_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a11bcd-4c6d-7a2a-9e6b-6037a1ce0295" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a11bcd-4c6d-76c8-a7c2-608209951b24" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a11bcd-4c6d-7a2a-9e6b-6037a1ce0295" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_01a11bcd-5e61-7712-af98-81ef5f193fb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_01a11bcd-4c6d-7a2a-9e6b-6037a1ce0295" xlink:to="loc_us-gaap_SubsequentEventMember_01a11bcd-5e61-7712-af98-81ef5f193fb7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedFromOtherParty_01a080e4-becb-776d-b8ba-b366aace997a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementAmountAwardedFromOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019f3773-1571-74c7-933a-c8fdc5ef6b7e" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedFromOtherParty_01a080e4-becb-776d-b8ba-b366aace997a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForLegalSettlements_01a11bcc-a585-71fe-9bb3-776abe637e36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForLegalSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019f3773-1571-74c7-933a-c8fdc5ef6b7e" xlink:to="loc_us-gaap_PaymentsForLegalSettlements_01a11bcc-a585-71fe-9bb3-776abe637e36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNumberOfPlaintiffs_019f3773-1571-7439-a491-79763af2edf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingencyNumberOfPlaintiffs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019f3773-1571-74c7-933a-c8fdc5ef6b7e" xlink:to="loc_us-gaap_LossContingencyNumberOfPlaintiffs_019f3773-1571-7439-a491-79763af2edf1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfOtherLongTermDebt_019ffe88-4b97-75b1-bd4c-3352926abcb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfOtherLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019f3773-1571-74c7-933a-c8fdc5ef6b7e" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfOtherLongTermDebt_019ffe88-4b97-75b1-bd4c-3352926abcb1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_NumberOfOutstandingLetterOfCredit_019f3773-1571-7c13-8d0d-8f0922672e70" xlink:href="hrbr-20251231.xsd#hrbr_NumberOfOutstandingLetterOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019f3773-1571-74c7-933a-c8fdc5ef6b7e" xlink:to="loc_hrbr_NumberOfOutstandingLetterOfCredit_019f3773-1571-7c13-8d0d-8f0922672e70" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019f3773-1571-74b9-83b5-9818df22e733" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019f3773-1571-74c7-933a-c8fdc5ef6b7e" xlink:to="loc_us-gaap_LineOfCredit_019f3773-1571-74b9-83b5-9818df22e733" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_019f3773-1571-7f18-bcc7-d87bea6be4c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019f3773-1571-74c7-933a-c8fdc5ef6b7e" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_019f3773-1571-7f18-bcc7-d87bea6be4c1" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/RelatedPartyTransactionsDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#RelatedPartyTransactionsDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/RelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019f3773-1572-70cc-918a-a7b58d3acc2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-1572-7ddc-89e1-4996c09355f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019f3773-1572-70cc-918a-a7b58d3acc2e" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-1572-7ddc-89e1-4996c09355f9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019f3773-1572-7c56-b7c5-46b9580363d1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-1572-7ddc-89e1-4996c09355f9" xlink:to="loc_srt_CounterpartyNameAxis_019f3773-1572-7c56-b7c5-46b9580363d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1572-7c56-b7c5-46b9580363d1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019f3773-1572-7c56-b7c5-46b9580363d1" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1572-7c56-b7c5-46b9580363d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1572-7441-a611-bb389fdda400" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019f3773-1572-7c56-b7c5-46b9580363d1" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1572-7441-a611-bb389fdda400" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AwacAviationIncMember_019f3773-1572-7ca2-b74c-a733861ad8d3" xlink:href="hrbr-20251231.xsd#hrbr_AwacAviationIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1572-7441-a611-bb389fdda400" xlink:to="loc_hrbr_AwacAviationIncMember_019f3773-1572-7ca2-b74c-a733861ad8d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019f3773-1572-78b7-b18d-f791fbcc39d8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-1572-7ddc-89e1-4996c09355f9" xlink:to="loc_srt_ProductOrServiceAxis_019f3773-1572-78b7-b18d-f791fbcc39d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019f3773-1572-78b7-b18d-f791fbcc39d8_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019f3773-1572-78b7-b18d-f791fbcc39d8" xlink:to="loc_srt_ProductsAndServicesDomain_019f3773-1572-78b7-b18d-f791fbcc39d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019f3773-1572-7359-9648-0c616c5a9f16" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019f3773-1572-78b7-b18d-f791fbcc39d8" xlink:to="loc_srt_ProductsAndServicesDomain_019f3773-1572-7359-9648-0c616c5a9f16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_FinancialAdvisoryAndManagementServicesMember_019f3773-1572-7c16-88df-0dcb1618185a" xlink:href="hrbr-20251231.xsd#hrbr_FinancialAdvisoryAndManagementServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019f3773-1572-7359-9648-0c616c5a9f16" xlink:to="loc_hrbr_FinancialAdvisoryAndManagementServicesMember_019f3773-1572-7c16-88df-0dcb1618185a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f3773-1572-7d08-a721-7904e305c6e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-1572-7ddc-89e1-4996c09355f9" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f3773-1572-7d08-a721-7904e305c6e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019f3773-1572-7d08-a721-7904e305c6e3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f3773-1572-7d08-a721-7904e305c6e3" xlink:to="loc_us-gaap_RelatedPartyDomain_019f3773-1572-7d08-a721-7904e305c6e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019f3773-1572-7274-82df-557d35789b34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019f3773-1572-7d08-a721-7904e305c6e3" xlink:to="loc_us-gaap_RelatedPartyDomain_019f3773-1572-7274-82df-557d35789b34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019f3773-1572-73df-81bd-a3d6655b4241" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019f3773-1572-7274-82df-557d35789b34" xlink:to="loc_us-gaap_RelatedPartyMember_019f3773-1572-73df-81bd-a3d6655b4241" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7634-947a-371dc02ee9af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019f3773-1572-7ddc-89e1-4996c09355f9" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7634-947a-371dc02ee9af" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7634-947a-371dc02ee9af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7634-947a-371dc02ee9af" xlink:to="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7634-947a-371dc02ee9af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f3773-1572-76aa-9289-304959c7604e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7634-947a-371dc02ee9af" xlink:to="loc_us-gaap_ClassOfStockDomain_019f3773-1572-76aa-9289-304959c7604e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SeriesCRedeemableConvertiblePreferredStockMember_019f3773-1572-7f76-82a3-d30df44f0998" xlink:href="hrbr-20251231.xsd#hrbr_SeriesCRedeemableConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f3773-1572-76aa-9289-304959c7604e" xlink:to="loc_hrbr_SeriesCRedeemableConvertiblePreferredStockMember_019f3773-1572-7f76-82a3-d30df44f0998" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_019f60e7-5def-78fa-bd50-6584dcb720e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f3773-1572-76aa-9289-304959c7604e" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_019f60e7-5def-78fa-bd50-6584dcb720e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentForManagementFee_019f3773-1572-7fb7-9a2a-e9e07bb75fa2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentForManagementFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019f3773-1572-70cc-918a-a7b58d3acc2e" xlink:to="loc_us-gaap_PaymentForManagementFee_019f3773-1572-7fb7-9a2a-e9e07bb75fa2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AnnualRecurringFeePayableMonthlyPursuantToServiceAgreement_019f3773-1572-7f50-8d01-a4149223218e" xlink:href="hrbr-20251231.xsd#hrbr_AnnualRecurringFeePayableMonthlyPursuantToServiceAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019f3773-1572-70cc-918a-a7b58d3acc2e" xlink:to="loc_hrbr_AnnualRecurringFeePayableMonthlyPursuantToServiceAgreement_019f3773-1572-7f50-8d01-a4149223218e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TemporaryEquityStockIssuedDuringThePeriodSharesNewIssues_019f3773-1572-7e6d-9b65-801a706ca7f4" xlink:href="hrbr-20251231.xsd#hrbr_TemporaryEquityStockIssuedDuringThePeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019f3773-1572-70cc-918a-a7b58d3acc2e" xlink:to="loc_hrbr_TemporaryEquityStockIssuedDuringThePeriodSharesNewIssues_019f3773-1572-7e6d-9b65-801a706ca7f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_019f60e7-5def-7b21-8566-83f7f532dc44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockSharesConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019f3773-1572-70cc-918a-a7b58d3acc2e" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_019f60e7-5def-7b21-8566-83f7f532dc44" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/CollectiveBargainingAgreementsScheduleofMultiemployerPlansDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#CollectiveBargainingAgreementsScheduleofMultiemployerPlansDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/CollectiveBargainingAgreementsScheduleofMultiemployerPlansDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MultiemployerPlansLineItems_019f3773-1572-7e96-a289-aeaf990c088a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MultiemployerPlansLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfMultiemployerPlansTable_019f3773-1572-73b7-8ea8-7585b630b0a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfMultiemployerPlansTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MultiemployerPlansLineItems_019f3773-1572-7e96-a289-aeaf990c088a" xlink:to="loc_us-gaap_ScheduleOfMultiemployerPlansTable_019f3773-1572-73b7-8ea8-7585b630b0a9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollectiveBargainingArrangementAxis_019f3773-1572-71d2-af6d-744459cdd1fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollectiveBargainingArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfMultiemployerPlansTable_019f3773-1572-73b7-8ea8-7585b630b0a9" xlink:to="loc_us-gaap_CollectiveBargainingArrangementAxis_019f3773-1572-71d2-af6d-744459cdd1fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollectiveBargainingArrangementDomain_019f3773-1572-71d2-af6d-744459cdd1fe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollectiveBargainingArrangementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CollectiveBargainingArrangementAxis_019f3773-1572-71d2-af6d-744459cdd1fe" xlink:to="loc_us-gaap_CollectiveBargainingArrangementDomain_019f3773-1572-71d2-af6d-744459cdd1fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollectiveBargainingArrangementDomain_019f3773-1572-7c6b-afb4-530ef565496c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollectiveBargainingArrangementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CollectiveBargainingArrangementAxis_019f3773-1572-71d2-af6d-744459cdd1fe" xlink:to="loc_us-gaap_CollectiveBargainingArrangementDomain_019f3773-1572-7c6b-afb4-530ef565496c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_PilotsMember_019f3773-1572-7142-9204-1195128a32c2" xlink:href="hrbr-20251231.xsd#hrbr_PilotsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019f3773-1572-7c6b-afb4-530ef565496c" xlink:to="loc_hrbr_PilotsMember_019f3773-1572-7142-9204-1195128a32c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_DispatchersMember_019f3773-1572-7fa9-8081-710785825b1d" xlink:href="hrbr-20251231.xsd#hrbr_DispatchersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019f3773-1572-7c6b-afb4-530ef565496c" xlink:to="loc_hrbr_DispatchersMember_019f3773-1572-7fa9-8081-710785825b1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_MechanicsMember_019f3773-1572-70e0-b68a-194d41df374d" xlink:href="hrbr-20251231.xsd#hrbr_MechanicsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019f3773-1572-7c6b-afb4-530ef565496c" xlink:to="loc_hrbr_MechanicsMember_019f3773-1572-70e0-b68a-194d41df374d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TechnicalStoreClerksMember_019f3773-1572-7f5a-ae76-9f3ec309a621" xlink:href="hrbr-20251231.xsd#hrbr_TechnicalStoreClerksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019f3773-1572-7c6b-afb4-530ef565496c" xlink:to="loc_hrbr_TechnicalStoreClerksMember_019f3773-1572-7f5a-ae76-9f3ec309a621" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_FlightAttendantsMember_019f3773-1572-7ab4-9ac1-24d34d369a08" xlink:href="hrbr-20251231.xsd#hrbr_FlightAttendantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019f3773-1572-7c6b-afb4-530ef565496c" xlink:to="loc_hrbr_FlightAttendantsMember_019f3773-1572-7ab4-9ac1-24d34d369a08" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementCbaToAllEntitysEmployeesUnderCbaPercentage_019f3773-1572-7e81-a017-ce48f412d9d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementCbaToAllEntitysEmployeesUnderCbaPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MultiemployerPlansLineItems_019f3773-1572-7e96-a289-aeaf990c088a" xlink:to="loc_us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementCbaToAllEntitysEmployeesUnderCbaPercentage_019f3773-1572-7e81-a017-ce48f412d9d0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/IncomeLossPerShareandEquityAdditionalInformationDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#IncomeLossPerShareandEquityAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/IncomeLossPerShareandEquityAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019f3773-1572-71c1-9b5d-eda32efb31ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019f3773-1572-71c1-9b5d-eda32efb31ef" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7624-bd64-112776ce68c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019f3773-1572-71c1-9b5d-eda32efb31ef" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7624-bd64-112776ce68c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7624-bd64-112776ce68c3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7624-bd64-112776ce68c3" xlink:to="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7624-bd64-112776ce68c3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7b82-a996-c88f4a3276f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7624-bd64-112776ce68c3" xlink:to="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7b82-a996-c88f4a3276f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_019f3773-1572-7bd8-9116-c107e32fca3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7b82-a996-c88f4a3276f3" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_019f3773-1572-7bd8-9116-c107e32fca3f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_SeriesCRedeemableConvertiblePreferredStockMember_019f3773-1572-74ee-801a-6b249c681169" xlink:href="hrbr-20251231.xsd#hrbr_SeriesCRedeemableConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7b82-a996-c88f4a3276f3" xlink:to="loc_hrbr_SeriesCRedeemableConvertiblePreferredStockMember_019f3773-1572-74ee-801a-6b249c681169" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock_01a080fb-9c11-72dd-8adb-76f9a4e4bdba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock_01a080fb-9c11-72dd-8adb-76f9a4e4bdba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_019f3773-1572-73cd-bac3-9638dafae112" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockSharesConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_019f3773-1572-73cd-bac3-9638dafae112" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TemporaryEquityStockIssuedDuringThePeriodSharesNewIssues_019f3773-1572-7308-916f-2636f20bc0a6" xlink:href="hrbr-20251231.xsd#hrbr_TemporaryEquityStockIssuedDuringThePeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:to="loc_hrbr_TemporaryEquityStockIssuedDuringThePeriodSharesNewIssues_019f3773-1572-7308-916f-2636f20bc0a6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStock_019f3773-1572-7133-91ae-67585a71d53b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:to="loc_us-gaap_DividendsPreferredStock_019f3773-1572-7133-91ae-67585a71d53b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockLiquidationPreference_019f3773-1572-76fb-ab0e-a388baebf829" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockLiquidationPreference"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:to="loc_us-gaap_PreferredStockLiquidationPreference_019f3773-1572-76fb-ab0e-a388baebf829" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockConvertibleConversionPriceDecrease_019f3773-1572-710f-b169-4d80bf8eedd4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockConvertibleConversionPriceDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:to="loc_us-gaap_CommonStockConvertibleConversionPriceDecrease_019f3773-1572-710f-b169-4d80bf8eedd4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019f3773-1572-7be6-929f-72c17b30001e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_019f3773-1572-7be6-929f-72c17b30001e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TemporaryEquitySharesRedeemed_019f3773-1572-7169-ae22-f12fb9764fb5" xlink:href="hrbr-20251231.xsd#hrbr_TemporaryEquitySharesRedeemed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:to="loc_hrbr_TemporaryEquitySharesRedeemed_019f3773-1572-7169-ae22-f12fb9764fb5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_TemporaryEquityRedemptionValue_019f3773-1572-7cb8-a253-cebaffb57054" xlink:href="hrbr-20251231.xsd#hrbr_TemporaryEquityRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019f3773-1572-7099-99e5-cb92e092ec8a" xlink:to="loc_hrbr_TemporaryEquityRedemptionValue_019f3773-1572-7cb8-a253-cebaffb57054" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/StockRepurchaseProgramDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#StockRepurchaseProgramDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/StockRepurchaseProgramDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityClassOfTreasuryStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019f3773-1572-73f6-9d23-d75b88ed86c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019f3773-1572-73f6-9d23-d75b88ed86c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019f3773-1572-73f6-9d23-d75b88ed86c6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019f3773-1572-73f6-9d23-d75b88ed86c6" xlink:to="loc_us-gaap_EquityComponentDomain_019f3773-1572-73f6-9d23-d75b88ed86c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019f3773-1572-7ba5-afef-732ad0529ce9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019f3773-1572-73f6-9d23-d75b88ed86c6" xlink:to="loc_us-gaap_EquityComponentDomain_019f3773-1572-7ba5-afef-732ad0529ce9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019f3773-1572-7ed5-abd3-fba0c77fdda3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019f3773-1572-7ba5-afef-732ad0529ce9" xlink:to="loc_us-gaap_CommonStockMember_019f3773-1572-7ed5-abd3-fba0c77fdda3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_019f3773-1572-7d27-9d9e-1d52cdc03308" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:to="loc_srt_ShareRepurchaseProgramAxis_019f3773-1572-7d27-9d9e-1d52cdc03308" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019f3773-1572-7d27-9d9e-1d52cdc03308_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019f3773-1572-7d27-9d9e-1d52cdc03308" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019f3773-1572-7d27-9d9e-1d52cdc03308_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019f3773-1572-7860-ac4c-18c591b7a47a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019f3773-1572-7d27-9d9e-1d52cdc03308" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019f3773-1572-7860-ac4c-18c591b7a47a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_StockRepurchaseProgramMember_019f3773-1572-7f2a-822c-1b84cb489b87" xlink:href="hrbr-20251231.xsd#hrbr_StockRepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_019f3773-1572-7860-ac4c-18c591b7a47a" xlink:to="loc_hrbr_StockRepurchaseProgramMember_019f3773-1572-7f2a-822c-1b84cb489b87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019f3773-1572-75ea-9f6f-d76278186e54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019f3773-1572-75ea-9f6f-d76278186e54" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7326-84e4-24e63aa75245" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7326-84e4-24e63aa75245" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7326-84e4-24e63aa75245_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7326-84e4-24e63aa75245" xlink:to="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7326-84e4-24e63aa75245_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7e49-8352-d960a21083a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7326-84e4-24e63aa75245" xlink:to="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7e49-8352-d960a21083a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019f3773-1572-784e-b3cd-7b5d0fac039d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7e49-8352-d960a21083a8" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019f3773-1572-784e-b3cd-7b5d0fac039d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019f3773-1572-70f4-a11d-1d6a7b67b111" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019f3773-1572-70f4-a11d-1d6a7b67b111" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_StockRepurchaseProgramAutomaticIncreasePerCalendarMonthToAuthorizedAmount_019f3773-1572-7531-8cf7-4ff9f031d490" xlink:href="hrbr-20251231.xsd#hrbr_StockRepurchaseProgramAutomaticIncreasePerCalendarMonthToAuthorizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_hrbr_StockRepurchaseProgramAutomaticIncreasePerCalendarMonthToAuthorizedAmount_019f3773-1572-7531-8cf7-4ff9f031d490" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_FederalCorporateExciseTaxPercentage_019f3773-1572-7d89-ae8d-311729a30b1b" xlink:href="hrbr-20251231.xsd#hrbr_FederalCorporateExciseTaxPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_hrbr_FederalCorporateExciseTaxPercentage_019f3773-1572-7d89-ae8d-311729a30b1b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_ShareRepurchaseValueMinimumThresholdExemptFromTax_019f3773-1572-7a5b-bda2-e7a182b11532" xlink:href="hrbr-20251231.xsd#hrbr_ShareRepurchaseValueMinimumThresholdExemptFromTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_hrbr_ShareRepurchaseValueMinimumThresholdExemptFromTax_019f3773-1572-7a5b-bda2-e7a182b11532" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_ExciseTaxLiabilitiesIncurredDuringThePeriodAndCapitalized_019f3773-1572-7700-8ed0-98ee827a46dd" xlink:href="hrbr-20251231.xsd#hrbr_ExciseTaxLiabilitiesIncurredDuringThePeriodAndCapitalized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_hrbr_ExciseTaxLiabilitiesIncurredDuringThePeriodAndCapitalized_019f3773-1572-7700-8ed0-98ee827a46dd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_019f3773-1572-7f60-b9a4-60815e405719" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_019f3773-1572-7f60-b9a4-60815e405719" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Cash_019f3773-1572-7ea2-b2f6-8f0e6c1a491a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Cash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_us-gaap_Cash_019f3773-1572-7ea2-b2f6-8f0e6c1a491a" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/StockRepurchaseProgramDetails_1" xlink:type="simple" xlink:href="hrbr-20251231.xsd#StockRepurchaseProgramDetails_1"/>
  <link:definitionLink xlink:role="http://harbor.com/role/StockRepurchaseProgramDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityClassOfTreasuryStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019f3773-1572-73f6-9d23-d75b88ed86c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019f3773-1572-73f6-9d23-d75b88ed86c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019f3773-1572-73f6-9d23-d75b88ed86c6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019f3773-1572-73f6-9d23-d75b88ed86c6" xlink:to="loc_us-gaap_EquityComponentDomain_019f3773-1572-73f6-9d23-d75b88ed86c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019f3773-1572-7ba5-afef-732ad0529ce9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019f3773-1572-73f6-9d23-d75b88ed86c6" xlink:to="loc_us-gaap_EquityComponentDomain_019f3773-1572-7ba5-afef-732ad0529ce9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019f3773-1572-7ed5-abd3-fba0c77fdda3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019f3773-1572-7ba5-afef-732ad0529ce9" xlink:to="loc_us-gaap_CommonStockMember_019f3773-1572-7ed5-abd3-fba0c77fdda3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_019f3773-1572-7d27-9d9e-1d52cdc03308" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:to="loc_srt_ShareRepurchaseProgramAxis_019f3773-1572-7d27-9d9e-1d52cdc03308" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019f3773-1572-7d27-9d9e-1d52cdc03308_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019f3773-1572-7d27-9d9e-1d52cdc03308" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019f3773-1572-7d27-9d9e-1d52cdc03308_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019f3773-1572-7860-ac4c-18c591b7a47a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019f3773-1572-7d27-9d9e-1d52cdc03308" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019f3773-1572-7860-ac4c-18c591b7a47a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_StockRepurchaseProgramMember_019f3773-1572-7f2a-822c-1b84cb489b87" xlink:href="hrbr-20251231.xsd#hrbr_StockRepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_019f3773-1572-7860-ac4c-18c591b7a47a" xlink:to="loc_hrbr_StockRepurchaseProgramMember_019f3773-1572-7f2a-822c-1b84cb489b87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7326-84e4-24e63aa75245" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019f3773-1572-7259-ad68-fda9d3693533" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7326-84e4-24e63aa75245" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7326-84e4-24e63aa75245_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7326-84e4-24e63aa75245" xlink:to="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7326-84e4-24e63aa75245_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7e49-8352-d960a21083a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f3773-1572-7326-84e4-24e63aa75245" xlink:to="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7e49-8352-d960a21083a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019f3773-1572-784e-b3cd-7b5d0fac039d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f3773-1572-7e49-8352-d960a21083a8" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019f3773-1572-784e-b3cd-7b5d0fac039d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019f3773-1572-70f4-a11d-1d6a7b67b111" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019f3773-1572-70f4-a11d-1d6a7b67b111" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_StockRepurchaseProgramAutomaticIncreasePerCalendarMonthToAuthorizedAmount_019f3773-1572-7531-8cf7-4ff9f031d490" xlink:href="hrbr-20251231.xsd#hrbr_StockRepurchaseProgramAutomaticIncreasePerCalendarMonthToAuthorizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_hrbr_StockRepurchaseProgramAutomaticIncreasePerCalendarMonthToAuthorizedAmount_019f3773-1572-7531-8cf7-4ff9f031d490" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_FederalCorporateExciseTaxPercentage_019f3773-1572-7d89-ae8d-311729a30b1b" xlink:href="hrbr-20251231.xsd#hrbr_FederalCorporateExciseTaxPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_hrbr_FederalCorporateExciseTaxPercentage_019f3773-1572-7d89-ae8d-311729a30b1b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_ShareRepurchaseValueMinimumThresholdExemptFromTax_019f3773-1572-7a5b-bda2-e7a182b11532" xlink:href="hrbr-20251231.xsd#hrbr_ShareRepurchaseValueMinimumThresholdExemptFromTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_hrbr_ShareRepurchaseValueMinimumThresholdExemptFromTax_019f3773-1572-7a5b-bda2-e7a182b11532" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_ExciseTaxLiabilitiesIncurredDuringThePeriodAndCapitalized_019f3773-1572-7700-8ed0-98ee827a46dd" xlink:href="hrbr-20251231.xsd#hrbr_ExciseTaxLiabilitiesIncurredDuringThePeriodAndCapitalized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_hrbr_ExciseTaxLiabilitiesIncurredDuringThePeriodAndCapitalized_019f3773-1572-7700-8ed0-98ee827a46dd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_019f3773-1572-7f60-b9a4-60815e405719" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_019f3773-1572-7f60-b9a4-60815e405719" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Cash_019f3773-1572-7ea2-b2f6-8f0e6c1a491a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Cash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019f3773-1572-746b-825e-56608e66b3af" xlink:to="loc_us-gaap_Cash_019f3773-1572-7ea2-b2f6-8f0e6c1a491a" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://harbor.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="hrbr-20251231.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://harbor.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019f3773-1572-73cf-afa6-889f728be773" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_us-gaap_SubsequentEventTable_019f3773-1572-73cf-afa6-889f728be773" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019f3773-1572-7091-9e95-5a985043ab92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019f3773-1572-73cf-afa6-889f728be773" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019f3773-1572-7091-9e95-5a985043ab92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019f3773-1572-7091-9e95-5a985043ab92_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019f3773-1572-7091-9e95-5a985043ab92" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019f3773-1572-7091-9e95-5a985043ab92_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019f3773-1572-7107-a145-24a17c393341" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019f3773-1572-7091-9e95-5a985043ab92" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019f3773-1572-7107-a145-24a17c393341" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019f3773-1572-76cc-8869-8150690d1112" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019f3773-1572-7107-a145-24a17c393341" xlink:to="loc_us-gaap_SubsequentEventMember_019f3773-1572-76cc-8869-8150690d1112" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019f3773-1572-7b5f-a460-809197c7d69a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019f3773-1572-73cf-afa6-889f728be773" xlink:to="loc_srt_CounterpartyNameAxis_019f3773-1572-7b5f-a460-809197c7d69a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1572-7b5f-a460-809197c7d69a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019f3773-1572-7b5f-a460-809197c7d69a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1572-7b5f-a460-809197c7d69a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1572-76ed-8b42-755829601038" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019f3773-1572-7b5f-a460-809197c7d69a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1572-76ed-8b42-755829601038" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AirWisconsinMember_019f3773-1572-75f0-9469-96bd213a6efe" xlink:href="hrbr-20251231.xsd#hrbr_AirWisconsinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019f3773-1572-76ed-8b42-755829601038" xlink:to="loc_hrbr_AirWisconsinMember_019f3773-1572-75f0-9469-96bd213a6efe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_019f3773-1572-7dd3-84d3-52fe9f94073a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019f3773-1572-73cf-afa6-889f728be773" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_019f3773-1572-7dd3-84d3-52fe9f94073a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_019f3773-1572-7dd3-84d3-52fe9f94073a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_019f3773-1572-7dd3-84d3-52fe9f94073a" xlink:to="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_019f3773-1572-7dd3-84d3-52fe9f94073a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_019f3773-1572-7052-97ac-569f18067483" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_019f3773-1572-7dd3-84d3-52fe9f94073a" xlink:to="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_019f3773-1572-7052-97ac-569f18067483" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredBonusMember_019f3773-1572-79b4-a31f-ee746407483e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredBonusMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_019f3773-1572-7052-97ac-569f18067483" xlink:to="loc_us-gaap_DeferredBonusMember_019f3773-1572-79b4-a31f-ee746407483e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019f3773-1572-793f-ae3d-ed89188c0d09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019f3773-1572-73cf-afa6-889f728be773" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019f3773-1572-793f-ae3d-ed89188c0d09" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019f3773-1572-793f-ae3d-ed89188c0d09_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019f3773-1572-793f-ae3d-ed89188c0d09" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019f3773-1572-793f-ae3d-ed89188c0d09_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019f3773-1572-7493-b7ea-6f0478a4506c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019f3773-1572-793f-ae3d-ed89188c0d09" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019f3773-1572-7493-b7ea-6f0478a4506c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019f3773-1572-7956-97cf-4459ba4979cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019f3773-1572-7493-b7ea-6f0478a4506c" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019f3773-1572-7956-97cf-4459ba4979cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019f3773-1572-73f5-afd5-f32931469459" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019f3773-1572-73cf-afa6-889f728be773" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019f3773-1572-73f5-afd5-f32931469459" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019f3773-1572-73f5-afd5-f32931469459_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019f3773-1572-73f5-afd5-f32931469459" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019f3773-1572-73f5-afd5-f32931469459_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019f3773-1572-7507-a690-0f59d5f73198" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019f3773-1572-73f5-afd5-f32931469459" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019f3773-1572-7507-a690-0f59d5f73198" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_AviationDispositionMember_019f3773-1572-7adf-b043-443f44859fc0" xlink:href="hrbr-20251231.xsd#hrbr_AviationDispositionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019f3773-1572-7507-a690-0f59d5f73198" xlink:to="loc_hrbr_AviationDispositionMember_019f3773-1572-7adf-b043-443f44859fc0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a0c225-1583-70a0-b3ef-7356cdcbfbd7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019f3773-1572-73cf-afa6-889f728be773" xlink:to="loc_srt_RangeAxis_01a0c225-1583-70a0-b3ef-7356cdcbfbd7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a0c225-1583-70a0-b3ef-7356cdcbfbd7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a0c225-1583-70a0-b3ef-7356cdcbfbd7" xlink:to="loc_srt_RangeMember_01a0c225-1583-70a0-b3ef-7356cdcbfbd7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a0c225-1583-705f-8bce-4baec58d64f6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a0c225-1583-70a0-b3ef-7356cdcbfbd7" xlink:to="loc_srt_RangeMember_01a0c225-1583-705f-8bce-4baec58d64f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a0c225-4ca8-780c-8537-8b8b8a81ec9e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a0c225-1583-705f-8bce-4baec58d64f6" xlink:to="loc_srt_MinimumMember_01a0c225-4ca8-780c-8537-8b8b8a81ec9e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a0c225-1583-7957-b112-527b430a3dce" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a0c225-1583-705f-8bce-4baec58d64f6" xlink:to="loc_srt_MaximumMember_01a0c225-1583-7957-b112-527b430a3dce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_NumberOfPurchaseAgreements_019f3773-1572-73d1-aadc-438826fd64c6" xlink:href="hrbr-20251231.xsd#hrbr_NumberOfPurchaseAgreements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_hrbr_NumberOfPurchaseAgreements_019f3773-1572-73d1-aadc-438826fd64c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_019f3773-1572-7db9-b317-16f8385c2896" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_019f3773-1572-7db9-b317-16f8385c2896" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_DisposalGroupIncludingDiscontinuedOperationConsiderationTaxObligationEstimates_01a0811a-cb65-7523-8b05-3c22d8d89b9b" xlink:href="hrbr-20251231.xsd#hrbr_DisposalGroupIncludingDiscontinuedOperationConsiderationTaxObligationEstimates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_hrbr_DisposalGroupIncludingDiscontinuedOperationConsiderationTaxObligationEstimates_01a0811a-cb65-7523-8b05-3c22d8d89b9b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_hrbr_DisposalGroupIncludingDiscontinuedOperationNetAssets_01a11cd3-c1a1-7a96-91f5-632b0308b104" xlink:href="hrbr-20251231.xsd#hrbr_DisposalGroupIncludingDiscontinuedOperationNetAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_hrbr_DisposalGroupIncludingDiscontinuedOperationNetAssets_01a11cd3-c1a1-7a96-91f5-632b0308b104" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_01a11cd3-092b-7ff5-8e67-41deaac7731d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_01a11cd3-092b-7ff5-8e67-41deaac7731d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation_01a11cd3-2f2d-7dbd-a127-ad83c15690cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation_01a11cd3-2f2d-7dbd-a127-ad83c15690cb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_01a11cd1-d2b8-7eb7-bdbe-63e92546b668" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_01a11cd1-d2b8-7eb7-bdbe-63e92546b668" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_01a0c48f-b96f-7fd8-9020-4b028590eea9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_01a0c48f-b96f-7fd8-9020-4b028590eea9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualCashAwardGrantedAmount_019f3773-1572-7ab1-8b9a-fa5e97bf3f80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCompensationArrangementWithIndividualCashAwardGrantedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualCashAwardGrantedAmount_019f3773-1572-7ab1-8b9a-fa5e97bf3f80" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualRecordedLiability_01a11cc4-8e40-79d1-a412-c0c2ff512d64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCompensationArrangementWithIndividualRecordedLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019f3773-1572-7fc8-a247-611db01086df" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualRecordedLiability_01a11cc4-8e40-79d1-a412-c0c2ff512d64" xlink:type="arc" order="9"/>
  </link:definitionLink>
</link:linkbase>
