Chugalug 2
There is a known time for them leaving the Aldergove CTZ and a known time for impact. The average groundspeed between those 2 points was 158 kts and groundspeed at impact, whilst attempting an escape manouvre, was conspicuously similar at approx 150 kts(AAIB).
The Yachtsman could see that the Mull was shrouded in cloud and the Chinook passed approx 200 ft above him. It flew straight on, without deviation, until the final desperate attempted escape manouvre.
They were in control of the Aircraft at Waypoint change and they were in control for that final attempted manouvre. There was no evidence of any technical malfunction that could have caused the crash.
What you have to do is come up with evidence - not hypothesis - that proves the existence of a major systems failure so serious that it prevented the Pilots from transmitting a Distress Call, Squawking Emergency, activating a Distress Beacon or even getting their Pax to adopt Crash Positions. You would also have to explain how such a malfunction managed to disappear without trace and how it is that there has been no repetition of such a malfunction in the 15 years since this tragedy.
I would point out that no such evidence has yet been produced.