NigD,
We (Sikorsky)just certified the Honeywell helicopter Mark XXII EGPWS working with the FAA.
The system's logic is substantially different than that used for airplanes, and a much more detailed internal terrain map so it is quite nuisance free. It took some careful development in the mountains of North Carolina (where "Last of the Mohicans" was filmed) to get it right. The box also has about 30 other protections, such as low on ILS, RAWS and settling after takeoff. It generates a radar-like terrain map that projects on the radar display, and also aural and visual caution and warning.
Here is a pointer to a HW press release:
http://www.egpws.com/general%20infor...famborough.PDF