41Section 3TERRAIN AlertsTERRAIN Failure AlertThe 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 ‘TERRAINhas failed’ (Figure 3-5).‘TERRAIN Not Available’ AlertThe TERRAIN system requires a 3D GPS navigation solution along with specific vertical accuracyminimums. Should the navigation solution become degraded, if the terrain/obstacle database is notavailable, or if the aircraft is out of the database coverage area, the annunciation ‘TERRAIN NOTAVAILABLE’ is displayed on the TERRAIN Page (Figure 3-6).Figure 3-5: ‘TERRAIN has failed’ messageFigure 3-6: ‘TERRAIN NOT AVAILABLE’ display
