Taws-B Limitations; Computing Gps Altitude For Taws - Garmin GTN 625 Pilot's Manual

10.3.2
Foreword
NOTE: The data contained in the TAWS databases comes from government
Getting
agencies. Garmin accurately processes and cross-validates the data but
Started
cannot guarantee the accuracy and completeness of the data.
Xpdr Ctrl
TAWS displays terrain and obstructions relative to the altitude of the aircraft.
Compliance with TAWS B alerts and warnings is MANDATORY. When a TAWS
Com/Nav
B "pull up" annunciation is issued, the pilot is required to pull up.
FPL
TAWS uses terrain and obstacle information supplied by government sources.
Terrain information is based on terrain elevation information in a database that
Direct-To
may contain inaccuracies. Individual obstructions may be shown if available in
the database. The data undergoes verification by Garmin to confirm accuracy of
Proc
the content, per TSO-C151c.
Wpt Info
10.3.3
TAWS uses information provided from the GPS receiver to provide a horizontal
Map
position and altitude. GPS altitude is derived from satellite measurements. GPS
altitude is converted to a Mean Sea Level (MSL)-based altitude (GSL altitude)
Traffic
and is used to determine TAWS alerts. GSL altitude accuracy is affected by
Terrain
factors such as satellite geometry, but it is not subject to variations in pressure
and temperature that normally affect pressure altitude devices. GSL altitude does
Weather
not require local altimeter settings to determine MSL altitude. Therefore, GPS
altitude provides a highly accurate and reliable MSL altitude source to calculate
Nearest
terrain and obstacle alerts.
Services/
The terrain and obstacle databases used by TAWS are referenced to Mean Sea
Music
Level. Using the GPS position and GSL altitude, TAWS displays a 2-D picture of
the surrounding terrain and obstacles relative to the position and altitude of the
Utilities
aircraft. Furthermore, the GPS position and GSL altitude are used to calculate
System
and "predict" the aircraft' s flight path in relation to the surrounding terrain
and obstacles. In this manner, TAWS can provide advanced alerts of predicted
Messages
dangerous terrain conditions.
Symbols
Appendix
Index
10-6

TAWS-B Limitations

Computing GPS Altitude for TAWS

Garmin GTN 625/635/650 Pilot's Guide 190-01004-03 Rev. F