Sox - hear hear!
Nick's post is interesting in that he confirms my suspicions that he helped develop the helicopter version of the EGPWS (the MkXXII) by tweaking the software from the fixed-wing version (which is why in my post I had to exclude NL in the group of people who didn't know how it works).
But Nick you did a very poor job and if it were me I certainly wouldn't want anyone to know I was responsible, or at least that I did some of the test flying (I doubt you single-handedly wrote the software though I am sure you would like to imply that). You also picked the wrong guy to try to bull**** because I am very familiar with all the modes you mention.
Nick is correct that, excluding the E part of EGPWS which relates to the terrain database, there are a number of basic GPWS modes. He is incorrect when he says various other things including that it has all the functions of AVAD.
With version 24 of the software, to which the SB he links to refers, the Mk XXII became compliant with the letter of the JAR-OPS 3.660 which is the requirement for radalt voice alerting. When originally introduced into Europe on the S92 (pre v24) it did not, though there was a work-around which was not fail safe but which the JOEB reluctanly had to accept or ground the aircraft. But even with v24, AVAD is not well replicated. Yes there is now the uncancellable 100' callout but there is no satisfactory substitute for "check height".
There are a couple of Mode 6 callouts that could be considered but neither the "altitude" nor the "minimums" callouts are acceptable - one only works with the gear up and the other only gives one warning - you will not get a second warning unless you either climb 200' or land, so its by no means safe for use with ARAs etc.
AVAD uses attenson tones to attact attention to the messages. These attensons were the result of substantial research carried out in the UK into voice messages - but of course not invented in the USA so not in EGPWS
These is the primary reasons why one of the larger oil companies has decided to delay implementation of EGPWS until the software is improved, and why Eurocopter's offering has to revert to the basic aircraft tones when you descend throught he bugged radalt height.
So now lets look at some of these wonderful modes that Nick mentions. He denies they are hang-overs from fixed wing but I will let you be the judge of that:
Mode 1 - this must be really useful because its permanently inhibited on the S92! Its "excessive sinkrate" but to trigger it you have to enter a sinkrate / height zone bordered by a line joining 10' and 900'/min, 20' and 1200'/min, 500' and 3000'/min. So you could be at 1199'/min descent rate and 21' - one second from impact - and not get a warning. Very useful! Its clearly aimed at not giving a warning to large fixed wing who come hurtling down the ILS to roundout height.
Mode 2 - this is inhibited when the terrain awareness data has high integrity, which is likely to be most of the time so not much use then. Even if it is working its sub-mode 2A (gear up in the cruise) has a high trigger threshold eg 1300'/min at 30' as does mode 2B (takeoff and landing - gear down) eg 3625'/min at 300' and 2375'/min at 100' and its not operative below 100'.
Mode 3 - descent after takeoff. This actually might have some value for night rig takeoffs, though nothing a PNF monitoring doesn't give you. And unfortunately it doesn't become active until you reach 50kts IAS or put the gear up.
Mode 4 seems to be more to do with high speed level flight with the gear up ( mode 4A) or gear down (4B). The former seems to be a reminder to put the gear down and the latter to give you a ticking-off for that fast low pass! Its boundaries are 120kts at 100' reducing to 80kts at 10'. Protection against inadvertant entry into these zones is better given by AVAD, but I suppose if you are stuck with EGPWS this mode might help a bit.
Mode 5 monitors ILS approaches and lets you know you are below glideslope. We carry PNF for that and with modern fully coupled aircraft it doesn't have much value. It may cause nuisance warnings as you might be doing a visual approach with the ILS tuned in. Yes there is an inhibit button but that's another cockpit action required.
And lastly (thank God) Mode 6 which does various callouts - the two I mentioned earlier as poor AVAD sustitutes plus bank angle callout, though with modern quadruplexed-autopilot aircraft I am not sure of the usefullness of this. And there is one for tailrotor strike (excessive pitch attitude at low level). Sounds good until you consider the elevated helideck landing case - as you come in with the tail below deck level the radalt is still seeing the sea etc so no warning until it goes crunch!
So overall I would rather have AVAD!
Nick does point out the blindingly obvious - ie some offshore helicopters fly overland for a bit. This is of course true though in the case of the N Sea, not much and the land is pretty flat. But I can see that the E bit of EGPWS would have some value for some operations - but have we considered the following:
Why would we need the E- bit? On an IFR flight we should of course be above MESA or whatever but sometimes mistakes are made so yes, EGPWS gives protection there without a doubt. On a VFR flight its for when we go inadvertant IMC. But I wonder how tempting it will be to continue a VFR flight you should otherwise have given up on cosy in the knowledge that the EGPWS will keep you right. Will EGPWS bring out the cowboy in us and lead to increased accidents? Only time will tell.
I forgot to mention that yipee the terrain database will show us the oil platforms. But this will definitely suck us into disaster as it will not show semi-subs etc - ie only part of the picture and that renders it dangerous in my opinion.
Well I think that's enough for one post - looking forward to Nick's blusterous response!
HC
ps can't resist a final dig when NL mentions "crack prevention of critical parts". I guess he had temporarily forgotten that, apart from the numerous (non life-threatening) aircrame cracks the 92 experiences, there has recently been a withdrawl from service of a number of S92 gearboxes due to their casings cracking! Now that's what I would call a critical part!
Last edited by HeliComparator; 4th Nov 2006 at 21:50.