Garmin GNC420W GPS Receiver User Manual


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Detailed Description of Feature Changes
1. TSO
TSOC-129/C-129aallowedtheuseofGPSfor
supplementalnavigationfornon-precisionapproaches.
AninstallationmeetingTSO-146arequirementsallows
theuseofyour400W/500Wnavigatorsastheprimary
navigationdeviceforprecisionapproaches.
See your dealer for detailed information about how the
new TSO affects the operation of your aircraft.
2. WAAS Capable
WAAS(WideAreaAugmentationSystem)isa
systemtoprovideimprovedintegrityandaccuracyof
GPSsignalsusedfornavigation.“WideArea”refersto
anetworkofgroundreferencestationsthatcoverthe
entireU.S.andsomeofCanadaandMexico.Imple-
mentedbytheFAA(FederalAviationAdministration)
foraviationusers,thesereferencestationsarelocated
atpreciselysurveyedspotsandcompareGPSdistance
measurementstoknownvalues.Eachreferencestationis
linkedtoamasterstation,whichputstogetheracorrec-
tionmessageandbroadcastsitviasatellite.The corrected
differentialmessageisthenbroadcastthroughoneoftwo
geostationarysatellites.Theinformationiscompatible
withthebasicGPSsignalstructure,whichmeansany
WAAS-enabledGPSreceivercanreadthesignal.WAAS
capablereceiverstypicallyhaveaccuraciesofonemeter
horizontallyand2metersvertically.
Basically,it’sasystemofsatellitesandgroundsta-
tionsthatprovideGPSsignalcorrections,givingyou
evenbetterpositionaccuracy.Howmuchbetter?Try
anaverageofuptovetimesbetter.AWAAS-capable
receivercangiveyouapositionaccuracyofbetterthan
twometers95percentofthetime.Andyoudon’thaveto
purchaseadditionalreceivingequipmentorpayservice
feestoutilizeWAAS.WAASalsoprovidesthecapabil-
ityofquicklydeterminingwhensignalsfromagiven
satellitearewrongandremovingthatsatellitefromthe
navigationsolution.
TheFederalAviationAdministration(FAA)andthe
DepartmentofTransportation(DOT)aredeveloping
theWAASprogramforuseinprecisionIFRapproaches.
WithoutWAAS,GPSalonedoesnotmeettheFAA’s
navigationrequirementsforaccuracy,integrity,and
availability.WAAScorrectsforGPSsignalerrorscaused
byionosphericdisturbances,timing,andsatelliteorbit
errors,anditprovidesvitalnearreal-timeintegrityinfor-
mationregardingthehealthofeachGPSsatellite.
Currently,WAASsatellitecoverageisonlyavailable
inNorthAmerica.Therearenogroundreferencesta-
tionsinSouthAmerica,soeventhoughGPSusersthere
canreceiveWAAS,thesignalhasnotbeencorrected
andthuswouldnotimprovetheaccuracyoftheirunit.
ForsomeusersintheU.S.,thepositionoftheWAAS
satellitesovertheequatormakesitdifculttoreceive
thesignalswhentreesormountainsobstructtheviewof
thehorizon.WAASsignalreceptionisidealforaviation
applications.YourGarmin400W/500Wseriessystem
providesforprimaryGPSnavigationinareaswhereno
WAAScoverageisavailableusingaFaultDetectionand
Exclusion(FDE)RAIMalgorithm.
OthergovernmentsaredevelopingsimilarSatellite-
BasedAugmentationSystems(SBAS).InAsia,it’sthe
JapaneseMulti-FunctionalSatelliteAugmentationSystem
(MSAS),whileEuropehastheEuroGeostationaryNavi-
gationOverlayService(EGNOS).Oncethesesystems
arefullytestedandoperational,your400W/500Wseries
systemwillbecapableofusingthesesystems.
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