GNS 530(A) Pilot’s Guide and Reference
190-00181-00 Rev. E 13-7
SECTION 13
TAWS
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 13-5).
PDA alerting begins when the aircraft is within 15 nm
of the destination airport. PDA alerting ends when the air-
craft 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 13-5 PDA Alerting Threshold
TAWS Inhibit
TAWS also has an inhibit mode that deactivates the
FLTA/PDA aural and visual alerts. Pilots should use
discretion when inhibiting TAWS and always remember
to enable the system when appropriate. Only the FLTA
and PDA alerts are disabled in the inhibit mode.
Inhibiting TAWS:
1) Select the TAWS Page and press the MENU Key.
‘Inhibit Terrain?’ is selected by default (Figure
13-6).
Figure 13-6 TAWS Page Menu
2) Press the ENT Key. The ‘TER INHB’ annunciation
is displayed in the TAWS annunciator field
when TAWS is inhibited (Figure 13-7).
Annunciator Field
Figure 13-7 Annunciator Field
Enabling TAWS:
1) Select the TAWS Page and press the MENU
Key. ‘Enable Terrain?’ is selected by default.
2) Press the ENT Key. The TAWS syste m is
functional again.