400/500 Series Garmin Optional Displays

Section 1: Introduction
Overview
PART THREE
TERRAIN INTERFACE
Garmin TERRAIN is a non-TSO-C151b-certified terrain awareness system incorporated into 400/500
Series units to increase situational awareness and aid in reducing controlled flight into terrain (CFIT).
TERRAIN functionality is a standard feature found in 400 Series units with main software version 5.01
or above, and in 500 Series units with main software version 6.01 or above, along with appropriate
hardware upgrades.
Operating Criteria
The Garmin TERRAIN system requires the following to operate properly:
• The system must have a valid 3D GPS position solution
• The system must have a valid terrain/obstacle database
GPS Position and GPS-MSL Altitude
Garmin TERRAIN uses information provided by the 400/500 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 terrain alerts.
GPS-MSL altitude accuracy is affected by factors such as satellite geometry, but 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.
Section 1
Introduction
Figure 1-1: The Garmin TERRAIN system offers many
of the features of Garmin TAWS but is non-TSO-
C151b-certified.
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