Some expert made the point that flying is so safe these days--because so many of the kinks have been worked out--that any major mishap involving a big commercial plane is likely to be a mystery, at least at first, and possibly permanently, almost guaranteed to have been caused by something unusual (like a suicidal pilot).
They do seem to have ruled out terrorism involving the two dudes with stolen passports, for whatever that's worth. They checked out their histories and current situations, and they appear to be (have been?) pretty ordinary guys. And we know that dying in a plane crash comes pretty close to the top of people's nightmare scenarios. Add in the possibility of terrorist involvement or, even scarier(?), a suicidal pilot and thinking about it could keep you awake nights.
