I have to agree with JimL, the issue has been talked around a bit without addressing specifics and I think that we now have a good list of considerations. I do think that a couple of other subjects need to be added to the pot.
WOW works well if you have W's. I recollect the efforts BHL went through with trying to give the 212 a sensor which told the Decca when the aircraft was on the ground. It was a real dog's dinner and regularly got damaged by deck nets and became more of a safety hazard.
As JimL has alluded to; it is hugely more complicated to tell the helicopter's navigation suite which phase of flight the aircraft is in and tune the 'enviroment sensors' accordingly. The differentiation between the two working environments of 'Offshore' and 'On Shore' needed to be made. What works on the North Sea or somewhere in the viscinity of Eket does not necessarily work for the EMS guys trying to find the hospital.
Fundamentally a pilot needs to know when he is in danger and how soon it's going to happen, be it other traffic or the terrain. Nuisance warnings will only create negative attitudes towards the efficency of the system. GPWS went through the same birth pains when it was developed and required several tuning cycles to minimise the spurious messages. I can still remember the AVAD irritating me on a day VFR shuttle when the inhibit button had either been forgotten or not pushed hard enough, however on an IMC ARA it was a good friend, especially at night, though I always found it strange that you would do one of the most demanding IMC-VMC transitions in the aviation world during a night ARA and inhibit one of the safety systems which would tell me that I was heading towards the sea with low airspeed, while trying to pick the deck out from the other mass of lights.
I am deeply suprised at comments from HC about the incident he describes where the navigation system displaced the EGPWS database. In the suite we use in the A330, we need to be in what is known as 'GPS Primary' or 'Nav Accuracy High' to be able to use the EGPWS function. If there is a Nav Accuracy Downgrade then the EGPWS should be inhibited by design.
The whole thing about Terrain Clearance Floor is important, as JimL says you don't need to know about the obstacle you are landing on. There must be a way for the EGPWS to inhibit the destination location since the navigation suite is programmed to take you there. Going back to the recent Zurich flight, while being vectored around bits of Germany and Switzerland, we only saw a few brown and green bits of EGPWS terrain since the aircraft knew we were using runway 28 for the approach. We only saw things that were important.
I am also very disappointed at the quality of the S92 Nav Display with the EGPWS overlay. It seems very curious that the best use of colour has not been employed and the system is giving information that is somewhat redundant. Maybe its the type I am now flying, but generally I feel a pilot should be given information that he either requests through selection or is required for the safe maintainance of flight trajectory. Does the sea really need to be blue?
On a slightly different note; with reference to mobile rigs, we even get affected by this issue. Singapore departures to the North East require special performance consideration to clear mobile obstacles in the channel between Malaysia and Singapore when activated by Notam, Due to the jack ups passing on their way in and out of port.
Regards
TOD