SFFP
The even bigger clue is the sworn evidence of the 2 Lighthouse Keepers (both trained Met Observers who routinely took meteorological observations as part of their Duties) who gave evidence to the BOI in respect of the actual weather on the Mull at the time of the crash.
Mr Murchie at the Lighthouse as the Chinook flew past overhead:
" I would estimate the visibility at this stage to be 15 to 20 metres at the most."
Mr Lamont driving to the Lighthouse from Campbeltown:
"The visibility, as I drove over the hill from Campbeltown to the lighthouse was down to only about 10 metres or less." The Chinook flew directly over Mr Lamont but he never saw it."
The Chinook impacted at approx 150 kts which equates to 77 metres/sec - however the aircraft was pitched nose up and yawing left in an apparent escape manoeuvre which would have reduced forward speed; thus the speed prior to that manoeuvre would have been greater than 150kts. It would be reasonable to say that the aircraft groundspeed was in the region of 80 metres per second which would have given only a quarter of a second visual warning at most prior to impact.
Further evidence was given by Mr Ellacott who was (ironically) looking for Aircraft accident sites who estimated that he was no more than 100 yards from the crash and the visibility was " nine or ten feet maximum."