GPS 400 Pilot’s Guide and Reference
190-00140-60 Rev. E
9-6
SECTION 9
TERRAIN
Table 9-3 shows system status annunciations that may also be issued:
Alert Type
TERRAIN Page
Annunciation
Pop-Up Alert
TERRAIN System Test Fail
None
TERRAIN Alerting is disabled
None
No GPS position or excessively degraded
GPS signal
None
System Test in progress
None
System Test pass
None
None
Table 9-3 Additional System Annunciations
Forward Looking Terrain Avoidance
The Forward Looking Terrain Avoidance (FLTA) alert is used by TERRAIN and is composed of:
• Reduced Required Terrain Clearance (RTC) and Reduced Required Obstacle Clearance (ROC) -These alerts are
issued when the aircraft flight path is above terrain, yet is projected to come within the minimum clearance
values in Table 9-4. When an RTC or ROC alert is issued, a potential impact point is displayed on the TERRAIN
Page.
• Imminent Terrain Impact (ITI) and Imminent Obstacle Impact (IOI) - These 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 potential impact point displayed on the TERRAIN Page. The alert is annunciated when the
projected vertical flight path is calculated to come within minimum clearance altitudes in Table 9-4.
During the final approach phase of flight, 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.
Phase of Flight
Minimum Clearance
Altitude Level Flight (ft)
Minimum Clearance
Altitude Descending (ft)
Enroute
700
500
Terminal
350
300
Approach
150
100
Departure
100
100
Table 9-4 Minimum Terrain and Obstacle Clearance Values for FLTA Alerts
