Forward Looking Terrain Avoidance; Premature Descent Alerting - Garmin GTN 625 Pilot's Manual

10.5.3.3

Forward Looking Terrain Avoidance

Reduced Required Terrain Clearance (RTC) and Reduced Required
Obstacle Clearance (ROC) alerts are issued when the aircraft flight path is
above terrain, yet is projected to come within the minimum clearance values in
the FLTA Alert Minimum Terrain and Obstacle Clearance Values table. When an
RTC alert and/or a ROC is issued, a threat location indicator is displayed on the
TAWS Page.
Imminent Terrain Impact (ITI) and Imminent Obstacle Impact (IOI)
alerts are issued when the aircraft is below the elevation of a terrain or obstacle
cell in the aircraft' s projected path. ITI and IOI alerts are accompanied by a
threat location indicator displayed on the TAWS Page. The alert is annunciated
when the projected vertical flight path is calculated to come within minimum
clearance altitudes in the following table.
Flight Phase
En Route
Terminal
Approach
Departure
Table 10-14 FLTA Alert Minimum Terrain and Obstacle Clearance Values
During final approach, FLTA alerts are automatically inhibited when the
aircraft is below 200 feet AGL while within 0.5 NM of the approach runway or
below 125 feet AGL while within 1.0 NM of the runway threshold.
10.5.3.4

Premature Descent Alerting

A Premature Descent Alert (PDA) is issued when the system detects that the
aircraft is significantly below the normal approach path to a runway.
PDA alerting begins when the aircraft is within 15 NM of the destination
airport and ends when the aircraft is either 0.5 NM from the runway threshold
or is at an altitude of 125 feet AGL while within 1.0 NM of the threshold. During
the final descent, algorithms set a threshold for alerting based on speed, distance,
and other parameters.
190-01004-03 Rev. F
Minimum Clearance Altitude (feet)
Level Flight
700
350
150
100
Garmin GTN 625/635/650 Pilot's Guide
Descending
500
300
100
100
10-49
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