Calculated Height Above Ground - Garmin GTS 820 TAS Pilot's Manual

fault clears, the GTS unit will go into Operate mode if it was operating prior to
the fault.

6.7 Calculated Height Above Ground

For aircraft that are not equipped with a radar altimeter, the system can
calculate the height above ground using information from various optional
interfaces. This calculation can enable additional functionality (such as ground
traffic filtering), without requiring a radar altimeter interface.
NOTE: The Calculated Height Above Ground feature is only available in
GTS 800, GTS 820, and GTS 850 systems with system software version
4.00 or later; and only available in GTS 825 and GTS 855 systems with
system software version 2.20 or later.
Height above ground can be calculated using data provided by a connected
display. If provided by the display, the GTS can use Height Above Terrain
provided by a display' s TAWS function, or it can calculate height above ground
using altitude data provided for nearby airports.
NOTE: Height above ground data from a connected display can only be
used by GTS 800, GTS 820, and GTS 850 systems with system software
version 4.00 and later; or by GTS 825 and GTS 855 systems with system
software version 3.00 and later.
Height above ground can be calculated using an internal airport database
and optional 3-D GPS interface. The system' s internal airport database contains
locations and elevations for airports throughout the world. By comparing the
3-D GPS position and altitude to the airport database, the ownship' s height
above ground can be calculated. If GPS altitude is not available, 2-D GPS input
(position only) can be used along with baro-corrected altitude from an air data
computer to perform the calculation.
Additionally, if the system has detected that it is on the ground, the on-
ground position and pressure altitude will be used as a known ground reference
point. If GPS position is not available, the on-ground altitude will still be used
as a reference point as long as the ownship is on the ground and for up to 60
seconds after takeoff.
190-00587-02 Rev. E Garmin GTS Traffic Systems
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