Gomer
So I take it that you are saying that the only reason to have it offshore is to stop you from flying into the water? In that case I would say that EGPWS is not the tool for that. As previously discussed in this thread, modes 1 - 5 of the GPWS bit give no realistic protection from flying into the water, and the mode 6 callouts emulate AVAD but are not as effective for the various reasons discussed earlier. The terrain display tells you that you are going to fly into the water if you look at it, but then so does the radalt.
I agree that for some operations the protection onshore is useful - though not if you obey the regulations and fly IFR at the proper height, or VFR in appropriate conditions.
And one detail we haven't mentioned yet is that the effectiveness of the system is predicated on the aircraft's navigation equipment knowing where it is. One time that the best pilot in the world might fly into a hill is if the navigation equipment is telling him that he is somewhere where he is not. Unfortunately the navigation equipment is also telling the EGPWS that it is somewhere that it is not, so when the aircraft gets "lost" the EGPWS will not stop you flying into a mountain.
This was the cause of a very near terrain miss of an EGPWS-equipped UK-operated scheduled fixed-wing flying in Africa a few years ago. It transpired that the basic GPWS modes were supressed by the software because the E bit was telling it that it couldn't possibly be that near the ground as according to its database and its position there was lots of fresh air under it. They missed the ground by about 50ft, still in IMC.
To be fair that aircraft was using FMS position derived from VOR/DME at the time, and the VOR was faulty. I would hope its less likely to occur with GPS positioning, and in helicopters the EPGWS installation can use a separate GPS position source (though not necessarily). But even so its possible to have a satellite error which would effect both the aircraft's and the EGPWS's receivers equally. RAIM should help to reduce that but its not clear from the product spec how the EGPWS handles loss of RAIM.
The fans will no doubt think this is all very unlikely and they are probably right - I am just pointing out that the system lacks inherent robustness. It relies on an accurate position and an accurate database and neither of these can be guaranteed.
Regarding your accusation of jealousy, you are incorrect and in fact I have been generating a resistive force against the fitting of EGPWS to the fleet I fly, because I am concerned about its overall effect on the safety of our particular operation. I am confident that we will have it just as soon as the product becomes better suited to the operating environment.
HC
Last edited by HeliComparator; 15th Nov 2006 at 21:49.