Terrain Proximity - Garmin Cirrus Perspective SR20 Pilot's Manual

HAZARD AVOIDANCE

6.5 TERRAIN PROXIMITY

Do not use Terrain Proximity information for primary terrain avoidance. Terrain Proximity is
WARNING:
intended only to enhance situational awareness.
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Perspective Terrain Proximity is a terrain awareness system that does not comply with TSO-C151b certification
standards. It increases situational awareness and aids in reducing controlled flight into terrain (CFIT). Do not
confuse Terrain Proximity with Terrain Awareness and Warning System (TAWS). TAWS is more sophisticated
and robust, and it is TSO-C151b certified. Terrain Proximity does not provide warning annunciations or voice
alerts. It only provides color indications on map displays when terrain and obstacles are within a certain altitude
threshold from the aircraft. Although the terrain and obstacle color map displays are the same, TAWS uses more
sophisticated algorithms to assess aircraft distance from terrain and obstacles.
Terrain Proximity requires the following components to operate properly:
• Valid 3-D GPS position
• Valid terrain/obstacle database
Terrain Proximity displays altitudes of terrain and obstructions relative to the aircraft position and altitude with
reference to a database that may contain inaccuracies. Terrain and obstructions are shown only if they are in the
database. Terrain and obstacle information should be used as an aid to situational awareness. They should never
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.
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The Perspective GPS receiver provides the horizontal position and altitude. GPS altitude is derived from
satellite position. GPS altitude is then converted to the height above geodetic sea level (GSL), which is the height
above mean sea level calculated geometrically. GSL altitude is used to determine terrain and obstacle proximity.
GSL altitude accuracy is affected by satellite geometry, but is not subject to variations in pressure and temperature
that normally affect pressure altitude sensors. GSL altitude does not require local altimeter settings to determine
MSL altitude. It is a widely-used MSL altitude source.
Terrain and obstacle databases are referenced to MSL. Using the GPS position and altitude, the Terrain Proximity
feature portrays a 2-D picture of the surrounding terrain and obstacles relative to the position and altitude of the
aircraft. GPS position and GSL altitude are used to calculate and predict the aircraft' s flight path in relation to
the surrounding terrain and obstacles. In this way, the pilot can view predicted dangerous terrain and obstacle
conditions.
Cirrus Perspective
370
by Garmin – Pilot's Guide for the SR20/SR22SR22T
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190-00820-08 Rev. A