Of course, what is 'probable' in this particular context inevitably comes down to 'matters of opinion', rather than 'matters of fact'. When what we, the BOI, and the two AMs were searching for was proof!
Let us review the standards of proof generally used when required to "act in judgement on someone else":
The BOI required a standard of 'absolutely no doubt whatsoever'. Pretty clear, and also a standard of proof that the President of the BOI felt unable to satisfy, and therefore made no finding of negligence. Of course his AMs did not feel so encumbered by the lack of 'proof'.
A slightly lower standard of proof, used in courts of law to determine the guilt of the most serious offenders, would be 'beyond reasonable doubt'. Of course, it may be possible to satisfy this standard, without statisfying the much higher standard of 'absolutely NO doubt whatsoever'.
A yet lower standard would be 'a balance of probability'. Perhaps surprisingly to some, this was the standard used by the subsequent Fatal Accident Inquiry at Paisley. Of course this lengthy judicial inquiry (at which all relevant parties received appropriate representation felt unable to criticise either pilot on the basis of the evidence THEN available.
Of course, much more evidence (non disclosed by the MOD at that time!) has subsequently come to light, NON of which favours the position of the MOD! Perhaps the conclusion would have been more critical of the MOD had they disclosed what had been requested!!
I would suggest the above is the true relevance of the word probable in the context of this accident.
Let right be done!