Relative Terrain Symbology - Garmin G1000 NXi Pilot's Manual

HAZARD AVOIDANCE
uses GSL altitude to determine alerts for the Terrain-SVT and TAWS-B systems. 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. Therefore, GSL altitude provides a highly accurate and reliable MSL altitude source to
calculate terrain and obstacle alerts.
The terrain and obstacle databases used by the terrain system are referenced to MSL. Using the GPS position
and GSL altitude, terrain system displays a 2-D picture of the surrounding terrain and obstacles relative to the
position and altitude of the aircraft. Furthermore, for the Terrain-SVT or TAWS-B systems, the system uses the
GPS position and GSL altitude to calculate and "predict" the aircraft' s flight path in relation to the surrounding
terrain and obstacles. In this manner, the Terrain-SVT or TAWS-B systems can provide advanced alerts of predicted
dangerous terrain conditions.
Baro-corrected altitude (or indicated altitude) is derived by adjusting the altimeter setting for local atmospheric
conditions. The most accurate baro-corrected altitude can be achieved by frequently updating the altimeter
setting to the nearest reporting station along the flight path. However, because actual atmospheric conditions
seldom match the standard conditions defined by the International Standard Atmosphere (ISA) model (where
pressure, temperature, and lapse rates have fixed values), it is common for the baro-corrected altitude (as read
from the altimeter) to differ from the GSL altitude. This variation results in the aircraft' s GSL altitude differing
from the baro-corrected altitude.

RELATIVE TERRAIN SYMBOLOGY

The terrain system uses colors and symbols to represent terrain and point obstacles (with heights greater than
200 feet above ground level, AGL) present in the databases relative to aircraft altitude. The system dynamically
adjusts these colors as the aircraft altitude changes, and after takeoff and landing.
While the aircraft is on the ground, the system displays relative terrain 400 feet or more above the aircraft
altitude using red, and terrain at less than 400 feet above aircraft altitude using black, as shown on the On-
Ground Legend. When the aircraft is in the air, the system displays relative terrain information using red,
yellow, green, and black, as shown on the In-Air Legend. As the aircraft transitions from on-ground to in-air, or
from in-air to on-ground, the display of relative terrain momentarily fades into the corresponding colors. For
Terrain-SVT or TAWS-B systems, if an alert occurs, the relative terrain colors transition to the In-Air Legend if
the On-Ground Legend was shown in order to provide the pilot with the most information possible.
The following figure shows the relative terrain coloring for the Terrain Proximity system.
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On-Ground Legend
Figure 6-59 Relative Terrain Legend
Garmin G1000 NXi Pilot's Guide for the Cessna NAV III
In-Air Legend
190-02177-02 Rev. A