Garmin GNC 420W Pilots Guide - Page 187

SECTION 10 TERRAIN 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 (Figure 10-5). PDA alerting begins when the aircraft is within 15 nm of the destination airport. PDA alerting ends when the aircraft is either: • 0.5 nm from the runway threshold OR • at an altitude of 125 feet AGL while within 1.0 nm of the threshold. 700 TERRAIN Inhibit TERRAIN also has an inhibit mode that deactivates the FLTA/PDA visual alerts. Pilots should use discretion when inhibiting TERRAIN and always remember to enable the system when appropriate. Inhibiting TERRAIN: 1) Select the TERRAIN Page and press the MENU Key. 'Inhibit Terrain?' is selected by default (Figure 10-6). 600 Figure 10-6 TERRAIN Page Menu 500 2) Press the ENT Key. The 'TER INHB' annunciation 400 is displayed in the TERRAIN annunciator field 300 when TERRAIN is inhibited (Figure 10-7). 200 "Too Low Terrain" Annunciator Field 100 Runway 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Threshold Distance From Destination Airport (nm) Figure 10-7 Annunciator Field Figure 10-5 PDA Alerting Threshold Enabling TERRAIN: 1) Select the TERRAIN Page and press the MENU Key. 'Enable Terrain?' is selected by default. 2) Press the ENT Key. The TERRAIN system is functional again. Height Above Terrain (Feet) 190-00140-20 Rev. K GNC 420(A) Pilot's Guide and Reference 10-7