[BBKing]

American pilot - 160kg :P

What sort of volume is 280kg of explosive? Cessnas aren't that roomy inside.

[I do hope MI5 aren't reading the next set of Google searches I'm about to do]

C-4 plastic explosive - 1.60 g/cc

1 cc is a cube 1cm on each side. 1000cm on each side is a cubic metre or 100x100x100 cc=10^6 cc

So 1m^3 of C-4 weighs 1 600 000 grams or 1 600 kg or 1.6 tonnes. This would be

a) Quite expensive (£24,00 0 or so)
b) Devastating
c) Heavier than the entire aircraft

200kg would be 1/8 of a cubic metre of C-4, or a cube 50cm on each side. That would fit in a Cessna, I think, and it would have a chance of getting into the air.

200kg is officially (for quarrying/demolition) unsafe up to 500m away - not that it will kill you, but 500m is a safe distance for the hoi polloi to stand at.

200kg will blow a hole through seven feet of reinforced concrete, roughly, if placed directly in contact. Obviously it's hard to park a Cessna close enough to the building to get the full effect.

So in the worst case scenario a Cessna with as much high-grade explosive as it can carry having a really lucky hit would probably knock a hole in the wall of the White House or Capitol and make life rather unpleasant within 100-200 metres. So getting down into the bunkers seems quite a sensible precaution.

I'm not going to post any links. I can hear helicopters coming!