Re Weather
Perhaps instead you should consider the letter written to the Daily Telegraph by Sqn Ldr Donald Kinch, a very experienced Maritime Captain in Peace and War, who stated:-
" In light winds and high relative humidity, layers of fog and low cloud form adjacent to the Mull to obscure the high ground completely. There are occasions when a relatively calm sea and a grey sky of similar hue merge, so that in otherwise good visibility a pilot flying in accordance with Visual Flight Rules may be unaware that he is about to enter a fog/cloud bank."
In this case, however, the weather forecast had specifically warned that there was a 30 per cent chance that the weather in the vicinity of the Mull would be below VFR limits. The Pilots should, therefore, have been prepared for the poor weather and that they would have to climb to Safety Altitude and/or alter their routing to avoid the bad weather.
They adopted neither of those options but continued at high speed and low level in deteriorating weather conditions directly towards the high ground.
There is never any excuse for a negligent discharge of a weapon on a firing range because if the rules are obeyed it would not happen. The same principle applies in this tragic case.