Pilot's Guide

Garmin G1000H
™
Pilot’s Guide for the Bell 407GX
190-01255-00 Rev. B340
HAZARD AVOIDANCE
6.3 HTAWS
WARNING: Do not use HTAWS information for primary terrain avoidance. HTAWS is intended only to
enhance situational awareness.
NOTE: The data contained in the HTAWS databases comes from government agencies. Garmin accurately
processes and cross-validates the data but cannot guarantee the accuracy and completeness of the data.
NOTE: Terrain data is not displayed when the aircraft is outside of the installed terrain database coverage
region.
HTAWS (Helicopter Terrain Awareness and Warning System) is designed to increase situational awareness
andaidinreducingcontrolledightintoterrain(CFIT).HTAWSprovidesvisualandauralannunciationswhen
terrainandobstaclesarewithinthegivenaltitudethresholdfromtheaircraft.Thevisualandauralalertsand
warnings are advisory in nature only.
HTAWSsatisesTSO-C194requirementsforcertication.
HTAWSrequiresthefollowingtooperateproperly:
•Avalidterrainandobstacledatabase
•Avalid3-DGPSpositionsolution
HTAWSusesterrainandobstacleinformationsuppliedbygovernmentsources.Terraininformationisbased
onterrainelevationinformationinadatabasethatmaycontaininaccuracies.Individualobstructionsmaybe
shownifavailableinthedatabase.ThedataundergoesvericationbyGarmintoconrmaccuracyofthecontent.
However,thedisplayedinformationshouldneverbeunderstoodasbeingall-inclusiveanddatamaybeinaccurate.
HTAWSusesinformationprovidedfromtheGPSreceivertoprovideahorizontalpositionandaltitude,along
withadditionalaltitudeinputfromanoptionalradaraltimeter.GPSaltitudeisderivedfromsatellitemeasurements.
GPSaltitudeisthenconvertedtotheheightabovegeodeticsealevel(GSL),whichistheheightabovemeansea
level(MSL)calculatedgeometrically.GSLaltitudeisusedtodetermineHTAWSalerts.GSLaltitudeaccuracy
isaffectedbysatellitegeometry,butisnotsubjecttovariationsinpressureandtemperaturethatnormallyaffect
pressurealtitudesensors.GSLaltitudedoesnotrequirelocalaltimetersettingstodetermineMSLaltitude.Itis
awidely-usedMSLaltitudesource.Therefore,GSLaltitudeprovidesahighlyaccurateandreliableMSLaltitude
sourcetocalculateterrainandobstaclealerts.
TheterrainandobstacledatabasesusedbyHTAWSarereferencedtoMSL.UsingtheGPSpositionandGSL
altitude,HTAWSdisplaysa 2-D pictureof thesurrounding terrainandobstacles relativetothe positionand
altitudeoftheaircraft.Furthermore,theGPSpositionandGSLaltitudeareusedtocalculateand“predict”the
aircraft’sightpathinrelationtothesurroundingterrainandobstacles.Inthismanner,HTAWScanprovide
advanced alerts of predicted dangerous terrain conditions.
HTAWSincorporatesaltitudeinputfromanoptionalradaraltimeterforcertainalerts.
Baro-correctedaltitude(orindicatedaltitude)isderivedbyadjustingthealtimetersettingforlocalatmospheric
conditions.  The most accurate baro-correctedaltitude can be achieved by frequently updating the altimeter
settingtothenearestreportingstationalongtheightpath.However,becauseactualatmosphericconditions
seldommatchthestandardconditionsdenedbytheInternationalStandardAtmosphere(ISA)model(where
pressure,temperature,andlapserateshavexedvalues),itiscommonforthebaro-correctedaltitude(asread