Dr Dre, you are correct, most are due to usually sudden onset of bad food, gastro or flu type illnesses.
Occasionally on very rare occasions someone has a totally out of the blue heart attack etc and just dies right there in the seat.
I remember a few stories where that happened before takeoff over the years. Guy sitting there pre start says something like, " I'm feeling really tired all of a sudden" and a few seconds later, they are gone.
Thankfully That of course is extremely rare.
Most of the other comments re backup, detecting threats/errors, workload levels, recency etc are all true as well.
Most of the time 2 is better than one but of course some recent disasters shows that is not always the case either, the SFO Asiana being a prime example. Again, thankfully, rare events but they could be rarer still.
Last edited by aussie027; 8th Aug 2014 at 06:46.
Reason: correction