Taws Self-Test - Garmin G500 Pilot's Manual

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4.3.3

TAWS Self-Test

During G500/G600 power-up, the terrain/obstacle database versions are
displayed along with a disclaimer to the pilot. At the same time, TAWS self-test
begins. One of the following aural messages is generated:
• "TAWS System Test OK"
• "TAWS System Failure"
TAWS information can be displayed on the MFD in the TAWS page of the
MAP page group. Terrain and obstacles with heights greater than 200 feet
Above Ground Level (AGL) are contained in the database.
Computing GPS Altitude for TAWS
TAWS uses information provided from the GPS receiver to provide a horizontal
position and altitude. GPS altitude is derived from satellite measurements.
GPS altitude is converted to a Mean Sea Level (MSL)-based altitude (GPS-MSL
altitude) and is used to determine TAWS alerts. GPS-MSL altitude accuracy is
affected by factors such as satellite geometry, but it is not subject to variations
in pressure and temperature that normally affect pressure altitude devices. GPS-
MSL altitude does not require local altimeter settings to determine MSL altitude.
Therefore, GPS altitude provides a highly accurate and reliable MSL altitude
source to calculate terrain and obstacle alerts.
The terrain and obstacle databases used by TAWS are referenced to Mean
Sea Level. Using the GPS position and GPS-MSL altitude, TAWS displays a 2-D
(or 3-D with SVT) picture of the surrounding terrain and obstacles relative to
the position and altitude of the aircraft. Furthermore, the GPS position and
GPS-MSL altitude are used to calculate 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 dangerous terrain conditions.
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Garmin G500/G600 Pilot's Guide 190-00601-02 Rev. J