Garmin GNS 400W Pilot's Manual & Reference

Also see for 400W Series: Supplemental Flight manual Pilot's guide addendum Manual supplement Pilot's guide addendum Quick reference guide

Contents

Garmin GNS 400W Pilot's Manual & Reference Manual pdf 52 page image

2 - NAV PAGES42 190-00356-00 Rev GNOTE: The data contained in the TERRAIN databasescomes from government agencies. Garmin accuratelyprocesses and cross-validates the data but cannotguarantee the accuracy and completeness of the data.TERRAIN AlertingTERRAIN uses information provided from the GPSreceiver to provide a horizontal position and altitude.GPS altitude is derived from satellite measurements. GPSaltitude is converted to a mean sea level (MSL)-basedaltitude (GPS-MSL altitude) and is used to determineTERRAIN alerts. GPS-MSL altitude accuracy is affectedby factors such as satellite geometry, but it is not subjectto variations in pressure and temperature that normallyaffect pressure altitude devices. GPS-MSL altitude doesnot require local altimeter settings to determine MSLaltitude. Therefore, GPS altitude provides a highly accurateand reliable MSL altitude source to calculate terrain andobstacle alerts.TERRAIN utilizes terrain and obstacle databases thatare referenced to mean sea level (MSL). Using the GPSposition and GPS-MSL altitude, TERRAIN displays a 2-Dpicture of the surrounding terrain and obstacles relativeto the position and altitude of the aircraft. Furthermore,the GPS position and GPS-MSL altitude are used tocalculate and “predict” the aircraft’s flight path in relationto the surrounding terrain and obstacles. In this manner,TERRAIN can provide advanced alerts of predicteddangerous terrain conditions. Detailed alert modes aredescribed later in this section.Baro-Corrected AltitudeBaro-corrected altitude (or indicated altitude) is derivedby adjusting the altimeter setting for local atmosphericconditions. The most accurate baro-corrected altitudecan be achieved by frequently updating the altimetersetting to the nearest reporting station along the flightpath. However, because actual atmosphere conditionsseldom match the standard conditions defined by theInternational Standard Atmosphere (ISA) model (wherepressure, temperature, and lapse rates have fixed values),it is common for the baro-corrected altitude (as read fromthe altimeter) to differ from the GPS-MSL altitude. Thisvariation results in the aircraft’s true altitude differing fromthe baro-corrected altitude.Terrain PageTo display the TERRAIN Page, select the NAVgroup and turn the small right knob until theTERRAIN Page is displayed. The page displays terraininformation, aircraft ground track, and GPS-derivedMSL altitude. Altitude is shown in increments of 20feet or in increments of 10 meters, depending on unitconfiguration. The “G” to the right of the MSL altitudedisplay reminds the pilot that altitude is GPS-derived.The TERRAIN Page has two selectable viewsettings:• 360˚ View—View from above aircraft depictingsurrounding terrain on all sides• 120˚ View—View of terrain ahead of and 60˚ toeither side of the aircraft flight pathTERRAIN PageNOTE: The TERRAIN Page gives a “Track Up” dis-play orientation, as indicated by the “TRK” labelshown on the display. This is the only orientationavailable on this page.Terrain Operation