A friend of mine, who flies gliders, was skiing at the time, and (as did everyone else on the slopes) heard the plane go over. He & his party realised it was dangerously low, & were astonished that anyone would fly in such weather (snowing heavily enough that skiing was difficult), & commented on it to each other. He subsequently realised that must have been only a few seconds before the crash. They didn’t hear the crash, perhaps because of the snow muffling sound. One comment was “flying through the Cairngorms at 4000 feet in near-zero visibility probably wasn’t the cleverest thing to do”.