Garmin GNS 430 Pilot's Manual And Reference page 199

TERRAIN Failure Alert
The TERRAIN system continually monitors several
system-critical items, such as database validity, hardware
status, and GPS status. Should the system detect a failure,
a message is annunciated 'TERRAIN has failed' (Figure
11-11).
Figure 11-11 'TERRAIN has failed' Message
'TERRAIN Not Available' Alert
The TERRAIN system requires a 3D GPS navigation
solution along with specific vertical accuracy minimums.
Should the navigation solution become degraded, if
the terrain and obstacle database is not available, or
if the aircraft is out of the database coverage area, the
annunciation 'TERRAIN NOT AVAILABLE' is displayed
on the TERRAIN Page (Figure 11-12).
Figure 11-12 'TERRAIN NOT AVAILABLE' Annunciation
GNS 430 Pilot's Guide and Reference
SECTION 11
TERRAIN
11-11