IFD500 Series Pilot Guide
4-50 Map Subsystem
PREMATURE DESCENT ALERT (PDA)
The PDA function is operational only in the vicinity of the origin or the
destination airport contained in the FMS flight plan. Specifically,
considering all of the runways at the origin and destination airports,
the aircraft must be between 1 and 5 nautical miles from the runway
nearest to the aircraft position.
Using the threshold elevation of the nearest runway and the current
aircraft altitude, the PDA function determines whether the aircraft is
hazardously below the normal approach path for that runway, based
on the criteria in the table below.
Range from nearest
runway
AGL Altitude Range in Which a
PDA Caution Alert is Generated
If a PDA alert has been triggered, a CAS message and aural alert
“Too Low Terrain” will be issued and repeat every 6 seconds until it is
acknowledged or the condition is no longer true. For the condition to
no longer be true, the aircraft must clear the alerting altitude by 100
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