Originally Posted by
Herod
An explanation please. I'm way out of the loop, having retired in '04, so before computer-generated approaches had come about. If the aircraft is carrying out a NPA, and has no ILS glidepath, would not the EGPWS be screaming well before this point? Back when, home base on one runway flew over an escarpment. At about 2 miles, suddenly the rad alt went from about 1,000' to 600' almost instantaneously. The GPWS (no EGPWS then) certainly shouted at that point.
My (probably out of date) copy of the A320 FCOM for GPWS suggests that mode 1, mode 4 and mode 5 might not have been triggered.
Mode 1 Excessive descent rate : they were on a 3° approach profile, which might not trigger mode 1?
Mode 4 Unsafe terrain clearance when not in landing configuration : they
were in landing configuration.
Mode 5 Descent below glideslope : The approach they were following had no glideslope, so this would not have triggered.
EGPWS has Modes 4A, 4B, and 4C, which should trigger with ground proximity, but only if the aircraft is not in landing configuration?
So it would seem that (E)GPWS cannot help a crew on an NPA with a mis-set QNH? Am I reading that right?
@FlightDetent: good post #95. Perhaps all NPA approach plates should publish Radio Altimeter
heights vs distance to the threshold, (having surveyed the actual terrain), instead of altitudes, which of course are based on the QNH set in the cockpit.
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