1GeneralThelandinggearconsistsoftwomaingearsandanosegear.Themaingearislocatedinboardofeachengine,aftoftherearwingspar.Thenosegearislocatedbelowtheaftbulkheadoftheflightcompartment.Breakingisprovidedbyfourbrakeassemblies,onemountedoneachmaingearwheel.Landinggearcontrolandindicationcomponentslocatedintheflightcompartmentinclude：thelandinggearselectorleverandindicationlights,manualextensionhandles,parkingbrakeleverandindicator,nosegearsteeringcontrolwheels,antiskidcontrolswitchandinoperativeindicator,andtheautobrakecontrolswitchanddisarmindicator.下一頁返回1GeneralThelandinggearishydraulicallyactuatedtoextendandretractbymeansofalandinggearselectorleverlocatedonthecenterinstrumentpanel（P2-2）.Whentheselectorleverisplacedintheupposition,allthreegearsretract.Eachmaingearretractsintothefuselage.Thenosegearretractsorextends.TheOFFpositionisthenormalcruisemodeandalllandinggearsarelockedupanddepressurized.AsolenoidlocksystemrestrictstheselectorlevertotheUPpositionwhentheairplaneisontheground.Thelandinggearnon-retractionduringtake-offphaseisakeyfactorinin-flightinterruptions.上一頁下一頁返回1GeneralItrepresentsroughly14%offleetreports.AlthoughsignificantdecreaseinratehasbeendemonstratedonATA32,thelargenumberofequipmentinvolvedinthelandinggearextension/retractionsequencestillgivesaremote,butwide,spreadoffailuremodes.TheproposalsgivenprovidesimpleandprovenadvicetosignificantlyreduceATA32relatedflightinterruptions.Thefirstone,relatedtogroundlockpinsandgroundlocksleeves,commonlycalled“safetydevices,”or“safetypins,”mayappearobviously.上一頁下一頁返回1GeneralHowever,theincreaseofflightinterruptionsreportedduetosafetydevicesforgottenonthelandinggearpriortotakeoff,combinedwithanincreaseofqueriesonthesubjectledustomakeknownAirbusoperatorexperiences.Theotheronerelatestothenoselandinggear（NLG）“flight/ground”indicationsystem.Thisitemaimstoaddressimprovementsandthustocorrectoneofthemaincontributingfactorstolandinggearretractionfailure.TheL/Gsystemssupporttheaircraftonthegroundandareoleo-pneumaticshockabsorbersthatabsorbtaxiandlandingloans.上一頁下一頁返回1GeneralDuringflighttheL/Gisretractedintothelandinggearbaysinthebellyoftheaircraft.WhentheL/Gisextendedorretracted,therelateddoorsclosetomaketheaerodynamiccontoursoftheaircraft.上一頁返回2SystemDescription2.1MainLandingGearandDoors（Ref.32-1-00）EachMLGhasanMLGlegwhichincludesanoleo-pneumaticshockabsorber.TheL/GretractsintotheavailablespaceofitsMLGbays.Atwo-piecesidestayassemblyholdstheMLGintheextendedposition.Alockstaykeepsthesidestayassemblystableinthelockdownposition.ThreedoorscloseeachMLGbay.Theseare：—ahydraulically-operatedmaindoor;下一頁返回2SystemDescription—amechanically-operatedhingeddoor;—afairingdoorontheMLGleg.AdooropeningmechanismletsthemaindoorbeopenedonthegroundforaccesstotheMLGbay.2.2NoseLandingGear(NLG)andDoors（Ref.32-20-00）Thenosedoorincludesanoleo-pneumaticshockabsorberandretractsforwardintoabayinthefuselage.Atwo-piecedragstrutassemblywithalockstaylocksthelegintheextendedposition.上一頁下一頁返回2SystemDescriptionThelegincludesahydraulically-operatedsteeringmechanism(Ref.AMMd/o32-51-00-00).FourdoorsandafairingclosetheNLGbay.Theseare：—twohydraulically-operatedforwarddoors;—twomechanically-operatedreardoors;—afixedfairingontheNLGleg.AdooropeningmechanismletstheforwarddoorsbeopenedonthegroundforaccesstotheNLGbay.上一頁下一頁返回2SystemDescription2.3ExtensionandRetraction(Ref.32-30-00)Thenormalextensionandretractionsystem（Ref.AMMD/O32-31-00-00）extendsandretracts：—theleftandrightMLGanddoors（Ref.AMMD/O32-11-00-00）and（Ref.AMMD/O32-12-00-00）;—theNLGanddoors（Ref.AMMD/O32-21-00-00）and（Ref.AMMD/O32-22-00-00）.Thesystemiselectricallycontrolledandhydraulicallyoperated.上一頁下一頁返回2SystemDescriptionTwoindependentlywiredelectricalsystemscontroltheoperationofthehydrauliccomponents.Eachsystemhas：—aLandingGearControlandInterfaceUnit（LGCIU）;—proximitysensorstoshowthepositionofL/Gcomponents.Thehydrauliccircuithasactuatorsthatextendandretractthegearsandopenandclosethedoors.Thegreenhydraulicsystem（Ref.AMMD/O29-11-00-00）suppliesthehydraulicpowertooperatetheactuators.Thesystemhastwoelectro-hydraulicvalvesthatcontroltheoperationofactuators.上一頁下一頁返回2SystemDescriptionOneelectro-hydraulicvalvecontrolstheactuatorsfortheL/G.Theothercontrolstheactuatorforthedoors.TheLGCIUmakestheselectionsofthevalveassemblytoretractorextendtheL/Gandmovethedoorsinagivensequence.TheindicatingandwarningdatafortheL/Garegivenin（Ref.AMMD/O32-61-00-00）.TheLGCIUalsohasBuilt-InTestEquipment（BITE）whichisgivenin（Ref.AMMD/O32-69-00-00）.Thefreefallextensionsystem（Ref.AMMD/O32-33-00-00）extendstheMLGandNLGifthenormalextensionandretractionsystemisnotavailable.上一頁下一頁返回2SystemDescriptionThesystemincludeselectricalrotary-typeactuatorsthatoperatemechanicallinkagestoopenthegearanddooruplocksandhydraulicvalves.Thisletsgravityextendthegears.2.4WheelsandBrakes（Ref.32-40-00）Thewheelsareofaluminumalloyandhaveatubelessradialorbiasplytype.Thenormalbrakingsystem（RefAMMD/O32-42-00-00）isusedtodecreasethespeedoftheaircraftwhenitmovesontheground.TheBrakeandSteeringControlUnit（BSCU）controlstheoperationofnormalbraking.上一頁下一頁返回2SystemDescriptionHydraulicpressureisnecessary.HydraulicpressureissuppliedfromtheGreenmainhydraulicsystem（RefAMMD/O29-11-00-00）.Thesystemhasmodesofoperation,manualandautomatic,andautomaticanti-skidportionineachmode.TheinputsignalsfromthebrakepedalsareproportionaltopedaltravelandsupplyindependentlytoMLGforautomaticbrakingthreePushbuttonSwitches（P/BSW）eachsetanautomaticbrakingprogram（LO,MEDorMAX）intheBSCU,whichgivesadifferentdecelerationrate,anautomaticbrakingprogram.TheBSCUusesthesignaltomakeoutputsignalswhichcontroltheoperationoftheelectrohydraulicValves.上一頁下一頁返回2SystemDescriptionIfthenormalbrakingsystemisnotavailable,controlautomaticallychangestooneofthealternatebrakingsystems（Ref.AMMD/O32-43-00-00）or（Ref.AMMD/O32-44-00-00）.Alternatebrakingwithanti-skidfunction（Ref.AMMD/O32-43-00-00）isasecondaryelectro-hydraulicbrakingsystem.Itisautomaticallyavailableifspecifiedfailuresoccurinthenormalbrakingsystem.Brakinginputsaremadeonlyatthebrakepedalsthroughalow-pressurehydraulicsystem.TheBSCUcontrolsfourservovalvesinthesystemtosupplytheanti-skidfunction.上一頁下一頁返回2SystemDescriptionThehydraulicpressurethatoperatesthebrakepistonsissuppliedfromYellowmainhydraulicpowersystem（Ref.AMMD/O29-13-00-00）.Alternatebrakingwithoutanti-skid（Ref.AMMD/O32-44-00-00）functionisthesecondarymodeoftheoperationofthealternatebrakingsystem.Brakinginputsaremadeonlyatthebrakepedals.Aselectricalpowerisnecessarytooperatethissystem,itisusuallyusedwhentheaircraftistowed.Thesystemoperatesfromtheaccumulatorsinthealternatebrakingsystem.上一頁下一頁返回2SystemDescription2.4.1BrakeTemperatureSystems（Ref.AMMD/O32-47-00-00）Thebraketemperaturesystemincludesatemperaturesensorateachbrakewhichmeasuresthetemperatureandsendsthedatatoabraketemperaturemonitoringunit.ThebraketemperaturesareshownautomaticallyonthewheelpageoftheECAMSystemDisplay（SD）.2.4.2BrakeCoolingSystems（Red.AMMD/O32-48-00-00）Thebrakecoolingsystemisamanuallycontrolledsystemthatdecreasesthetemperatureofthebrakeswhentheyaretoohot.Thesystemisusuallyusedonthegroundbutcanalsobeusedinflightifalandingisnecessaryimmediately.上一頁下一頁返回2SystemDescriptionThesystemincludesaP/BSWandanelectricallyoperatedfanineachMLGwheel.TheP/BSWhas：—aHOTlightthatshowsifthetemperatureofabrakeismorethanaspecifiedvalue;—anONlightthatshowswhentheswitchispushedin（selectedON）.2.4.3TirePressureIndicatingSystems（TPISs）（Ref.AMMD/O32-49-00-00）TheTPISincludesanelectronicsensoroneachwheelandaTirePressureIndicatingComputer（TPIC）.上一頁下一頁返回2SystemDescriptionTheTPICcontrolsandmonitorstheoperationofthesystemandsendsdatatootherinterfacedsystems.2.5Steering（Ref.32-51-00）ThesteeringsystemiscontrolledbytheBSCU（Ref.AMMD/O32-46-00-00）.Thesteeringsystemchangesthedirectionoftheaircraftwhenitmovesontheground.ThesystemusestheGreenmainhydraulic-powersystem（Ref.AMMD/O29-11-00-00）tooperateasteeringmechanismwhichchangesthedirectionoftheNLGwheels.ThetwohandwheeltransmittersinthecockpitsupplytheprimarysteeringinputstotheBSCU.上一頁下一頁返回2SystemDescriptionTherudderpedalsandtheautopilotsupplysecondaryinputtotheBSCUthroughtheflightcontrolprimarycomputers.Thesystemoperationcanbecancelledtoletthenosewheelsmovefreelyduringaircraftgroundmovement.ThesteeringsystemiscontrolledbytheBSCU（RefAMMD/O32-46-00-00）.Thesteeringsystemchangesthedirectionoftheaircraftwhenitmovesontheground.ThesystemusestheYellowmainhydraulic-powersystem（Ref.AMMD/O29-13-00-00）tooperateasteeringmechanismwhichchangesthedirectionoftheNLGwheels.上一頁下一頁返回2SystemDescriptionThetwohandwheeltransmittersinthecockpitsupplytheprimarysteeringinputstotheBSCU.TherudderpedalsandtheautopilotsupplysecondaryinputtotheBSCUthroughtheflightcontrolprimarycomputers.Thesystemoperationcanbecancelledtoletthenosewheelsmovefreelyduringaircraftgroundmovement.2.6PositionandWarning（Ref.32-60-00）Thepositionandwarningsystemhastwopartswhichare：—indicatingandwarning(Ref.AMMD/O32-61-00-00);—L/GBITE(REF.AMMD/O32-69-00-00).上一頁下一頁返回2SystemDescription（1）IndicatingandWarning(Ref.AMMD/O32-61-00).TheindicatingandwarningsystemhasproximitysensorsontheL/GandL/GdoorstogivepositiondatatotheLGCIU.IndicationisgiventotheflightcrewonECAMand：—L/Gcontrollever;—LDGgearannunciatorsonpanel402vu,ifspecifiedfailuresoccur;—awarnisgivenontheEngineDisplayUnit（EDU）（Ref.AMMD/O31-66-00-00）;—thefuelpageontheSD;上一頁下一頁返回2SystemDescription—theflightwarningcomputer（Ref.AMMD/O31-52-00-00）givesanaudibleandvisualwarntotheflightcrew.（2）L/GBITE(Ref.AMMD/O32-69-00-00).EachLGCIUcontainsBITEwhichcontinuouslymonitorsthesystemforfailures.TheBITEsuppliesdatatothecentralizedfaultdisplaysystem（Ref.AMMD/O31-30-00-00）：—todoasystemtestduringgroundmaintenance;—tosimulatedifferentL/Gconfigurationsduringmaintenance.上一頁返回3Operation/ControlandIndicating3.1Maingearanddoors3.1.1TakeoffOntakeofftheloadsontheMLGdecrease.Astheaircraftbecomesairborne,theshockabsorberextends,whichgivestheeffectofanincreaseinthelengthoftheleg.Thisletstheaircraftmovethroughalargeangleduringtakeoff.WhenL/GUPisselected,thehydraulicallyoperateddooropens.Thehydraulicpressureatthedownlockactuatorreleasestheovercenterlockofthelockstay.TheMLGactuatorretractstheMLGintothebay.下一頁返回3Operation/ControlandIndicatingDuringtheretractiontheBSCUautomaticallyputsthebrakesonforashorttime.Thisstopstherotationofthewheelsbeforetheygointothebays.ThehydraulicallyoperateddoorclosesaftertheMLGislockedintothebay.WhenL/GDOWNisselected,thehydraulicallyoperateddooropens.Theretractionactuatorextendstoextendtheleg.Thesidestayandthelockstaymovetotheovercenterpositiontolockthegearintheextendedposition.Thedoorclosesafterthegearisextended.Withthegearextendedtheshockabsorberabsorbsthelandinggearloads.上一頁下一頁返回3Operation/ControlandIndicating3.1.2NoseLandingGearandDoorsAstheNLGwheelsleavethegroundontakeoff,theshockabsorberextends.Thecaminthelegmakessurethatthewheelsareinthecenter.Whentheshockabsorberisfullyextended,theBSCUpreventssteeringoutputstothesteeringmechanism.WhentheL/GUPisselected,thehydraulicallyoperateddoorsopen.ThehydraulicpressureattheNLGdownlockactuatorreleasestheovercenterlockofthelockstay.ThedragstrutassemblyfoldsastheNLGretracts.Asthelegretracts,arotatingjointonthelegcutsoffthehydraulicpressuresupplytothesteeringsystem.上一頁下一頁返回3Operation/ControlandIndicatingThehydraulicallyoperateddoorscloseafterthegearislockedintothebay.3.1.3Extensionandretraction（1）NormalExtensionandRetraction：WhentheL/Gcontrolleverismoved,theLGCIUsendsacontrolsignaltotheelectrohydraulicsafetyvalve.TheLGCIUcontrolsthesequenceofoperationstoextendandretractthegearsandopenthedoors.TheLGCIUusesthepositiondatafromtheproximitysensors（Ref.AMMD/O32-61-00-00）tocontrolthesequenceofoperations.上一頁下一頁返回3Operation/ControlandIndicatingOnlyoneLGCIUcontrolsthesequenceofoperations.ControlchangesfromoneLGCIUtotheotheraftereachretraction/extensioncycle.（2）FreeFallExtension：Thefreefallextensionsystemiscontrolledbythefreeextensionhandleinthecockpit.ThefreefallextensionhandleisconnectedtotheL/Ganddooruplocks.Whenthehandleisturned,thedooruplocksaremechanicallyopenedbythecables.Whenthedoorsareopen,thelandinguplocksarealsomechanicallyopened.GravitythenextendstheL/G.SpringspulltheNLGlockstayortheMLGsidestayintothelockedpositionandtheL/Gdoorsstayopen.上一頁下一頁返回3Operation/ControlandIndicatingAmechanicallyoperatedvalveisolatesthehydraulicsupply.Othermechanicallyoperatedvalvesletfluidmoveintothehydrauliccomponentsofthenormalextensionandretractionsystem.Thispreventscavitationandhydrauliclocks.Thefreefallextensionsystemisresetwhen：—thefreefallextensionhandleisbackinitsoriginalconfiguration.—theL/Gcontrollever（6GA）isputinthedownposition.Hydraulicpoweristhenputbackintothenormalextension/retractionsystemandtheL/Gdoorsclose.上一頁下一頁返回3Operation/ControlandIndicating3.1.4BrakingandRelatedSystems（1）NormalBraking：IntheautomaticmodetheselectionofanAUTO/BPKP/BSW（LOMEDorMAX）setsaprogramtogiveasetdecelerationrate.TheBSCUautomaticallystartstheprogramwhentheaircraftconfigurationiscorrectandthencontrolsthepressuresenttothebrakes.Inthemanualmodethemovementofthebrakepedalsoperatesthebrake-pedaltransmitterunit.ThetransmitterunitsendsasignaltotheBSCUwhichinturnsendstherequiredinputsignaltotheservovalves.上一頁下一頁返回3Operation/ControlandIndicatingTheservovalvesletapressureinproportiontothepedaltravelgotothebrakes.TheBSCUalsocontrolstheanti-skidfunction.ItcomparestheMLGwheelspeedswiththeaircraftspeedandreleasesabrakeifthereareindicationsofaskid.（2）AlternateBraking：Whenthebrakepedalsareoperated,thelow-pressurehydraulicsystemoperatesadualvalve.Thisletsthehydraulicpressurefromtheyellowhydraulicsystemgotothesecondsetofpistonsinthebrakes.上一頁下一頁返回3Operation/ControlandIndicatingTheBSCUcontrolstheanti-skidfunction.IftheBSCUcannotsupplythiscontrol,brakingisinproportiontotheamountofpedaltravel.（3）ParkingBrakes（Ref.AMMD/O32-45-00-00）：WhentheparkbrakeselectorswitchissettoON,thepressurefromtheyellowhydraulicsystemortherelatedaccumulatorsissenttothesecondsetofpistonsinthebrakes.Whenthissystemisinuse,allotherbrakingsystemsarehydraulicallyisolated.（4）BrakeTemperatureSystems（Ref.AMMD/O32-47-00-00）：上一頁下一頁返回3Operation/ControlandIndicatingThebraketemperaturesystemcontinuouslymeasuresthetemperatureateachbrake.ThesensorateachbrakesendsasignaltoaBrakeTemperatureMonitorUnit（BTMU）.EachBTMUreceivesthesignalsfromapairofbrakesensorsandsendsthedatatotheBSCU.TheBSCUsendsthedatatootherinterfacesystems.（5）BrakeCooling（ifinstalled）（Ref.AMMD/O32-48-00-00）：WhentheP/BSWissettoON,thefansinthewheelshroudsturnandpullairthroughthebrakes.Thisdecreasesthetemperatureofthebrakesmorequickly.上一頁下一頁返回3Operation/ControlandIndicating（6）TirePressureIndicatorSystems（ifinstalled）（Ref.AMMD/O32-49-00-00）：TheTPISautomaticallymonitorsthetirepressureandshowsthesevaluesontheWHEELpageofthesystemdisplay（Ref.AMMD/O31-60-00-00）.Thetirepressureindicatingcomputeralsosuppliesotherdataandwarningswhenthepressuresareunsatisfactory.（7）Steering（Ref.AMMD/O32-51-00-00）：TheBSCUusesthesteeringinputsignalsfromthehandwheeltransmittersinthecockpittocalculate：上一頁下一頁返回3Operation/ControlandIndicating—thenecessarysteeringangle;—thenecessaryrateofmovement;—thedirectionoftheturn.Itthensendssteeringoutputsignalstotheelectro-hydrauliccomponentstooperatethesteeringmechanism.3.2IndicatingThedatafromtheL/GsystemsareshownontheWHEELpageofthesystemsdisplay（Ref.AMMD/O31-60-00-00）.Systemwarningsaregivenon：—theL/Gcontrollever（6GA）;上一頁下一頁返回3Operation/ControlandIndicating—thecockpitloudspeakers;—themasterwarningandcautionlights;—theEWD;—LDGGearUNLKannuniciators.Referto（Ref.AMMD/O31-60-00-00）fortheL/Gconfigurationandfaultwarnings.Forotherwarningsrefertothespecifiedchapter.上一頁返回4BITETestTheBITEhasthesefunctions