Pilot's Guide

Garmin G1000H
™
Pilot’s Guide for the Bell 407GX
190-01255-01 Rev. A372
HAZARD AVOIDANCE
6.4 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 preventing controlled ight into terrain (CFIT) accidents.  HTAWS providesvisualannunciations
andvoicealertswhenterrainandobstaclesarewithinthegivenaltitudethresholdfromtheaircraft.Thevisual
annunciations and voice 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.Garminveriesthedatatoconrmaccuracyofthecontent.However,thedisplayed
informationshouldneverbeunderstoodasbeingall-inclusiveandthedatamaystillcontaininaccuracies.
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.ThesystemusesGSLaltitude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