Please don't jump to conclusions on the motives behind my post above. I said I "wonder", because I do not know; I wasn't suggesting that I suspected this to be caused by a mechanical fault.
But on the point of "tactful", "helpful", and "perceptive"; I do not see what is morally questionable with being curious as to the cause - and I certainly don't think it's unhelpful. As someone who is interested in safety, I am all too aware that there are bound to be lessons that can be learned from this - as there are with every such accident. It is with no intention of disrespect to the victims or their families that I endeavour to learn something from this. Indeed they deserve to be shown the greatest amount of respect in what must be a very difficult time for them. However, is not the purpose of this forum to discuss the technicalities of such tragedies?