Originally Posted by
212man
...for the Mk XXII EGPWS the look ahead alert envelope shrinks below 100 KIAS and is inhibited below 70 KIAS? I'm not saying that is what happened, but it lends itself as an explanation.
I for one have done a bit of flying around with TAWS + MFD equipped helicopters in VMC and have often wondered why I don't get terrain warnings when I'd expect a warning was appropriate, and why I get warnings which I don't think to be necessary. I have a poor understanding of the logic being used in either case to warn, or not to warn. One of the IFR helicopters I was flying was fitted with the aeroplane version of the TAWS system (because it was cheaper) and that was next to useless in the helicopter operating environment.
I have come to the conclusion the system can't be relied upon 100% of the time, and if you're relying on it not to hit something, that reliance is not totally reliable.