GPS
Tandemrotor, I don't think your comments are too harsh, as I stated in the caveat, I had a minor connection with the incident, and have not followed the case since. I was aware of the political aspects of the accident but was surprised to see that 12 years later there was a very active thread on this board regarding the subject.
My involvement with GPS is that I spent 10 years working on integrated navigation for the MOD, mainly involved with algorithm design, Kalman filters etc. The basic theory is that GPS and INS are complementary data sources. The INS provides short term smoothing of the GPS data, and the GPS provides long term correction to the INS drift. With kalman filtering calibration of the INS can be performed and hence you end up with a closed loop integrated NAV system.
But when I started working in this field in the very early 90's there was no integrated NAV system as described above. At that time the INS was used to rate aid the GPS receiver to provide better tracking of GPS signal in high rate turns, and research concentrated on the fast jet environment.
In 94 the GPS on board the Chinook was almost certainly used as a stand alone system, it would not have had its data blended with other kit via kalman filtering etc.
I was suggesting a possible scenario that maybe (and who knows) the crew were flying in VMC and were confident that the GPS system was providing an accurate solution (but in error as discussed earlier by a few hundred meters maybe 500m ?? (again just an assumption). However, all the visual clues, the INS solution etc gave confidence that their position was known accurately, (isn't there a term for this in the psychological world when events/actions/ etc support an incorrect situation).
Anyway my post was merely to point out that GPS was not as accurate and reliable as many might have thought and it possible that the INS drift was in the same direction as any GPS error (if there was any) and an incorrect indication of the aircrafts position was provided to the crew.