Walter Kennedy
Could you please give us an estimate of how many hours were flown in HC2 Chinooks between the accident date and the first implementation of any of these changes? In other words, how much flying was done subsequent to the crash without any changes to the FADEC system? And, if the amount is sufficient to pass judgement on, how does this compare with expected/satisfactory reliability for a military aircraft?
I don't know though I could try and find out. It's worth bearing in mind the restrictions we now know existed at the time of the crash, which were supposed to reduce the risk of system problems, such as not switching the FADEC into reversionary (backup) mode because of unpredictable behaviour.
I couldn't imagine any supplier being able to sell a commercial system in which users were not able to have a backup facility. The lack of a reliable backup was potentially more serious in the case of the Mk2 because the FADEC was categorised by Boeing as safety-critical.
I can see why you'd want to compare the number of hours flown uneventfully after the Mull accident, before changes to the FADEC. That said, I've taken an interest in the probable causes of crashes of some commercial aircraft and it's not unusual for investigators, from the CVR and CDR, to discover a chain of events which hadn't been predicted by anyone, not even the manufacturer. So trying to apply any scientific analysis to what little we know from the Mull crash would seem to me to be of no value, or at best speculation.
Indeed to me the most striking technical thing about the Mull crash is how little independently-verified information there is. On what
is known, and has been verified by the AAIB - and the TANS information was given no AAIB endorsement - I do not see that any cause, probable cause, or even likely cause, can be established.
Much has been said about the waypoint change, as reported by Racal [now Thales]. The AAIB did not endorse Racal's report.