Walter,
Thank you for your prompt response.
I think we agree that WPt D is a precise location at Inverness. Whether it was obtained from an LZ chart, OS map, or consultation with ATC Inverness we will probably never know.
To try and explain what might have happened I have again tried to put myself in the position of the crew on that day.
Having decided on a precise LZ / Tgt, I would now shop around for an IP / TAP.
The corner of Fort George looks good.
I would draw a line from my IP to my target on the OS and measure the bearing and distance as accurately as possible. I would enter C as a bearing and distance from D. So would never have measured the Lat and Long. A precise IP to Target run defined none the less.
I would approach my IP with Track B to C selected, Bearing and Distance or A/A as required by the Captain. Once the TAP had been positively identified I would switch to Track C to D A/A to define precise run in to the LZ.
This technique was used at Lyneham, Farnboro and Boscombe by most Pilots and Navs. If it is not appropriate to Chinook operations, I am sure someone will tell me.
I accept the fact that the LZ I mentioned was unsuitable for Chinooks and there may well be others around. But if Google earth is correct Wpt A is still a pile of rocks. I would still expect to see a TAP to LZ run planned and as the lighthouse turning point Wpt A, is within acceptable plotting limits.
We are now probably boring everyone else to death. We are both working on unprovable theories. I you wish to continue this line please PM me.