[svandamme]

I doubt they were supposed to be on same altitudes at all.
pretty sure the flight plan and airshow rules prohibit that, they fly their own patterns with plenty of seperation.. And all they have to do in case of trouble, is steer out of the pattern.. all that is plenty briefed..

So my guess, the P63 pilot got incapacitated, while in his bend, at 80 something degrees, that means loosing altitude..

The freak part is that he didn't just go down on his own, imagine the odds that he is incapacitated and in that open sky , just happens to cross the B17's tail? second sooner or later and he would have missed it ..
I mean that is just incredible bad luck for the B17 crew.. it could easily have gone the other way of near miss and 'phew we got incredible lucky there".. but it didn't.. thats the freak part.

I'm sure airshow rules will become stricter from now on, I do suspect the show part resulted in too dynamic a flight for the sort of display they were doing (many planes)