Garmin GNC 420, Pilot'S Manual & Reference

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GNC 420(A) Pilot’s Guide and Reference
10-7
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
600
500
400
300
200
100
Height Above Terrain (Feet
)
Distance From Destination Airport (nm)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
“Too Low Terrain” “Too Low Terrain”
Runway
Threshold
Figure 10-5 PDA Alerting Threshold
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).
Figure 10-6 TERRAIN Page Menu
2) Press the
ENT
Key. The ‘TER INHB’ annunciation
is displayed in the TERRAIN annunciator field
when TERRAIN is inhibited (Figure 10-7).
Annunciator Field
Figure 10-7 Annunciator Field
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.
190-00140-20 Rev. K