Lonewolf
Many thanks, that is a superb link.
Also, thanks for the input to the questions I put. I think in retrospect they are all 'worse' than speculating that the Captain was on the lavatory or whatever. Your answers actually highlight the speculative nature of the questions, even if they 'demand' yes or no answers.
I think, as you mention, with a combination of events almost always to blame for such things, it may well be something no one has thought of is in the mix somewhere, rather than one 'key'.