Chi Meson said:OK reeling it in, and getting back to the OP:
Avoiding the rest of the conspiracy theories, whether or not it was really an American Airlines craft, whether it was the Jews, the Arabs, the Aliens, J. Edgar Hoover, whether or not we landed on the moon, whether or not Nessie eats eggs, if crop circles are a virus etc etc...
The "flash" is not the explosion... it is too soon to have anything to do with the explosion. THe flash is small and very brief. It seems to be some sort of friction or discharge or other sparking phenomenon caused by the aluminum nose cone striking the steel/concrete/glass side of the building.
The first thing I though about is how some stones spark when you strike them together, some other materials will spark when you snap them apart (Wintogreen lifesavers for example).
I am assuming that the flash was not due to tampering, because the purpose of this flash as evidece of a "detonator" is just too silly to discuss.
So, sticking to the "D" part of the S&D: what is a reasonable cause of this flash?
yes yes... It could also be due to the glass blowing outward from the building when it shattered, caused by higher pressure inside the building than outside.