Garmin GPS Receiver 400/500 User Manual download pdf (Page 47)

Section 3

TERRAIN Alerts

Forward Looking Terrain Avoidance

The Forward Looking Terrain Avoidance alert, or FLTA, is used by the TERRAIN system and is com-

posed of two elements:

• Reduced Required Terrain Clearance (RTC) Avoidance — Provides alerts when the aircraft ﬂight path is

above terrain, yet is projected to come within minimum clearance values outlined in Table 3-1. When an

RTC alert is issued, a potential impact point (see page 34) is displayed on the TERRAIN Page.

• Imminent Terrain Impact (ITI) Avoidance — Provides alerts when the aircraft is below the elevation

of a terrain cell in the aircraft’s projected path. ITI alerts are accompanied by a potential impact point

displayed on the TERRAIN Page. The alert is given when the projected vertical ﬂight path is calculated to

come within minimum clearance altitudes in the following table.

Phase of Flight Level Flight Descending

Enroute 700 ft. 500 ft.

Terminal 350 ft. 300 ft.

Approach 150 ft. 100 ft.

Departure 100 ft. 100 ft.

Table 3-1: Minimum Terrain Clearance Values for RTC/ITI Alerts

During the ﬁnal approach phase of ﬂight, RTC/ITI alerts are automatically inhibited when the aircraft

is below 200’ AGL while within 0.5 nm of the approach runway or is below 125’ AGL while within 1 nm

of the runway.

RTC/ITI TERRAIN Severity

‘TERRAIN AHEAD’ alert (ﬂashing)—Estimated poten-

tial impact in approximately 30 seconds after pop-up

alert and annunciation. Similarily, an ‘OBSTACLE

AHEAD’’ alert is also provided.

‘TERRAIN ADVISORY’ advisory—Estimated potential

impact in approximately 60 seconds after pop-up alert

and annunciation. Similarily, an ‘OBSTACLE

ADVISORY’ alert is also provided.

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Garmin GPS Receiver 400/500 User Manual Page 47