Garmin G3X Pilot’s Guide 190-01115-00 Rev. K228Hazard AvoidanceSystemOverviewFlightInstrumentsEISCNSInterfaceGPSNavigationFlightPlanningHazardAvoidanceAdditionalFeaturesAFCSAnnun/AlertsAppendixIndex7.2 TERRAINWARNING: Do not use Terrain information for primary terrain avoidance.Terrain information is intended only to enhance situational awareness.NOTE: Terrain data is not displayed when the aircraft is outside the installedterrain database coverage area.NOTE: Terrain depicted in the Profile View is always “ahead” of the aircraft,and will change as ground track changes.The Terrain Page displays altitudes of terrain and obstructions relative to the aircraftposition and altitude with reference to a database that may contain inaccuracies.Terrain and obstructions are shown only if they are in the database. Terrain andobstacle information should be used as an aid to situational awareness. They shouldnever be used to navigate or maneuver around terrain.Note that all obstructions may not be available in the terrain and obstacle database.No terrain and obstacle information is shown without a valid 3-D GPS position.The G3X GPS receiver provides the horizontal position and altitude of the aircraft.Aircraft GPS altitude is derived from satellite position. GPS altitude is then convertedto a mean sea level (MSL)-based altitude (GPS-MSL altitude) and is used to determineterrain and obstacle proximity. GPS-MSL altitude accuracy is affected by satellitegeometry, but is not subject to variations in pressure and temperature that normallyaffect pressure altitude sensors. GPS-MSL altitude does not require local altimetersettings to determine MSL altitude. It is a widely-used MSL altitude source.Terrain and obstacle databases are referenced to MSL. Using the GPS positionand altitude, the Terrain feature portrays a 2-D picture of the surrounding terrain andobstacles relative to the position and altitude of the aircraft. GPS position and GPS-MSL altitude are used to calculate and predict the aircraft’s flight path in relation to thesurrounding terrain and obstacles. In this way, the pilot can view predicted dangerousterrain and obstacle conditions.Alert windows appear on all pages (except the Terrain (TER) Page) to inform thepilot of proximity to the terrain and obstacles, as well as an unsafe descent rate. Thesealerts depend on user-defined parameters in the Terrain Page setup.
