Dalek
Would I spot an error of 1.5nms after 15 minutes over water with all the variables including W/V. Perhaps.
I do hope so. That's a hell of an error in such a short time. If they were VFR ,even if they were out by 3 or 4 miles they MUST have seen the coast. If you are saying that this aircraft was out of control and hurled itself into the scenery with the pilots unable to alter events that is a pretty long shot. It may not have been "airworthy" in the technical sense, but the crew accepted it as serviceable which to my mind is much more important.
As ever - a fascinating discussion.