The amount of planning they would have to put into that would be unreal!!
The chances of them actually getting it right on the day, very very slim!
If terrorists weighed those factors up, it would surely give them the nod to move onto something else.
There are so many open targets out there for them, and they are of course realising this now!!
And anyway, one for technical guys. Could a cessna or baron withstand the wake turbulance as it came close to impact, whilst 'following' a 747 down the glide? I dont think so!!