空中领航学(E-08)

AirNavigation空中领航学1北京航空航天大学飞行学院课件制作课程讲授王惠民AirNavigationAirNavigation空中领航学2Chapter8DMEDistance-measuringEquipment(DME)isaradionavigationaiddesignedtoprovidecontinuousindicationsofanaircraft’sdistancefromaselectedDMEgroundstation.Asanaidtovisualnavigation,thesystemmaybeusedforthefollowingpurposes:orientation;reportingdistances;andcalculatinggroundspeed.AirNavigation空中领航学3TheDMEsystemoperatesintheUHFfrequencybandandisoftenreferredtoasthe1,000MHzDME,sincetheoperatingfrequenciesarebetween960MHzand1,215MHz.ItisimportanttonotethatDMEfrequenciesarenottuneddirectlybythepilot.Inmostcases,theDMEispairedwithaVOR.WheneveroneofthesefrequenciesisselectedontheVHF–NAVset,theassociatedUHFDMEfrequencyisautomaticallytunedontheDMEreceiver(providedoneisfittedandswitchedon).TheDMESystemAirNavigation空中领航学4Thereare252separatechannelsavailableforDME.Eachchannelisnumberedform1t0126,followedbyeitheranXoraYsuffix,givingatotalof252differentdesignations.InAustralia,theDMEgroundstationsarenormallyco-locatedwithVORtransmitterstoprovidebearinganddistancemeasurementcapability.AirNavigation空中领航学5DMEequipmentinstalledinAustralianlightaircraftiscommonlyoftheVAN-Xtype,whichincludesacombinedindicatorandcontrollerunitfittedtotheinstrumentpanel.ThisusesadigitaldisplaytoindicateDMEdistance,rateofclosureandtimetothestation(inminutes).TypicalDMEindicator.AirNavigation空中领航学6DMEpositions,frequenciesandMorse-codeidentsforDMEstationsaregivenin:•EnRouteSupplementAustralia(ERSA);•enroutecharts(ERCs);•visualnavigationcharts(VNCs);and•visualterminalcharts(VTCs).WheretoFindDetailsofaDMEAirNavigation空中领航学7IdentisMCOFrequencyChannelChannelGeographicalpositionDMEinformationintheERSA.AirNavigation空中领航学8DMEinformationontheERC.DMEinformationontheVTC.AirNavigation空中领航学9OperationoftheDME.AirNavigation空中领航学10DMEOperatingPrinciplesDMEoperatesonasimilarprincipletoradar.TheairborneDMEequipmenttransmitsacontinuousseriesofradiopulses,knownasinterrogationpulses.Thegroundstationinterrogatesthesepulsesandiftheyareacceptabletransmitsaseriesofreplypulsesbacktotheaircraft.TheDMEequipmentintheaircraftisabletomeasurethetimeintervalbetweenthetransmissionoftheinterrogationpulsesandthereceptionofthereplypulsesfromthestation.Thiselapsedtimeisthenconvertedintoanequivalentdistance.AirNavigation空中领航学11RangeandRatedCoverageAnyreductionistheusablerangeofaDMEduetointerveningterrainmayusuallybeovercomebyclimbingtoahigheraltitude.TerrainmayblockthereceptionofVHF(andUHF)signals.AirNavigation空中领航学12AnextractfromtheAIPshowingtheratedcoverageforVORandDMEgroundstations.AirNavigation空中领航学13DMEAccuracyTheonlysignificantlimitationoftheDMEarisesfromthefactthatitmeasuresthestraight-linedistancebetweentheaircraftandthegroundstation,whichistheslantdistance.TheslantdistancewillalwaysbegreaterthantheactualgrounddistancebetweentheaircraftandtheDMEstation.ThegreaterthedistancefromtheDMEstation,thelesstheslanterror.Duringstationpassage,aredfailureflagwillusuallyappeartoshowthatthesignalsareunusable.AirNavigation空中领航学14DMEmeasuresslantdistance.TheDMEwillindicatetheheightoftheaircraftoverheadtheDMEstation..AirNavigation空中领航学15DMEdistanceactuallyrepresentsacircularpositionlinearoundthegroundstation.AnaircraftreceivingtheDMEislocatedsomewherealongthisline.DMEstationsareoftenco-locatedwithVORorNDBtransmitters.WhenacircularpositionlinederivedfromDMEindicationsisusedinconjunctionwithastraightpositionlineobtainedfromaco-locatednavaid,itispossibletoestablisharadiofix.Suchafixwillbeveryaccurate,becausethepositionlinesintersecteachotherat90°.AcircularpositionlinefromaDME.AirNavigation空中领航学16DMEpositionlinesmustbeusedcarefullytoensurethatradiofixeshaveadequateaccuracy(thatis,intersectatnotlessthan45°.)AirNavigation空中领航学17AthirdpositionlinemayberequirediftwoDMEarcsareusedtoestablisharadiofix.AirNavigation空中领航学18FindingGroundspeedUsingtheDMAIftheaircraftistrackingdirectlytowardsorawayfromthestation,thentherateofclosurewillbeequaltothecurrentgroundspeed.AquickmethodforcheckingthecurrentgroundspeedistonotetheDMEdistancecoveredin1/100ofanhour(36s).Simplymultiplyingthisdistanceby100willgivethedistancetravelledin1hr,whichisthegroundspeedinknots.AirNavigation空中领航学19Asaroughruleofthumb,donotusetheDMEforagroundspeedcheckwhenyouarehigherthan5,000ftandcloserthan10DME.DonotusetheDMEforgroundspeedcheckswhentrackingabeamtheDMEgroundstation.TrackingabeamaDMEgroundstation.AirNavigation空中领航学20