Garmin GNC 420W Pilot's Manual Addendum

Also see for GDL 69: Pilot's guide addendum Pilot's guide addendum Activation Instructions Pilot's guide Activation Instructions

Contents

Garmin GNC 420W Pilot's Manual Addendum Manual pdf 31 page image

27Part Three: Section 1TAWS IntroductionPart Three:TAWS InterfaceSection 1: IntroductionOverviewGarmin’s Terrain Awareness Warning System(TAWS) is an optional feature (500W-series only) toincrease situational awareness and aid in reducingcontrolled flight into terrain (CFIT). Garmin TAWSsatisfies TSO-C151b Class B requirements forcertification. Class B TAWS is required for all Part 91turbine aircraft operations with six or more passengerseats and for Part 135 turbine aircraft operationswith six to nine passenger seats (FAR Parts 91.223,135.154).Garmin TAWS satisfies TSO-C151b Class Brequirements for certificationOperating CriteriaGarmin TAWS requires the following to operateproperly:• The system must have a valid 3D GPS positionsolution• The system must have a valid terrain/obstacledatabaseGPS Position and GPS-MSL AltitudeGarmin TAWS uses information provided fromthe 500W Series GPS receiver to provide a horizontalposition and altitude. GPS altitude is derived fromsatellite measurements. GPS altitude is converted toa Mean Sea Level (MSL)-based altitude (GPS-MSLAltitude) and is used to determine TAWS alerts. GPS-MSL Altitude accuracy is affected by factors such assatellite geometry, but is not subject to variations inpressure and temperature that normally affect pressurealtitude devices. GPS-MSL Altitude does not requirelocal altimeter settings to determine MSL Altitude.Therefore, GPS altitude provides a highly accurate andreliable MSL altitude source to calculate terrain andobstacle alerts.TAWS Alerting using the GPS Position/GPS-MSLAltitudeGarmin TAWS utilizes terrain and obstacledatabases that are referenced to Mean Sea Level(MSL). Using the GPS Position and GPS-MSLAltitude, Garmin TAWS portrays a 2D picture ofthe surrounding terrain and obstacles relative to theposition and altitude of the aircraft. Furthermore,the GPS Position and GPS-MSL Altitude are usedto calculate and “predict” the aircraft’s flight path inrelation to the surrounding terrain and obstacles. Inthis manner, the Garmin TAWS system can provideadvanced alerts of predicted dangerous terrainconditions. Detailed alert modes are described furtherin Part Three, Section 3.Baro-Corrected Altitude verses GPS-MSL AltitudeBaro-Corrected Altitude (or Indicated Altitude)is derived by adjusting the altimeter setting for thelocal atmospheric conditions. The most accurateBaro-Corrected Altitude can be achieved by frequentlyupdating the altimeter setting to the nearest reportingstation along the flight path. However, because actual