Reply #72: more fuel, bigger explosion

[TrogL]

Teeny weeny fighter jets don't carry much fuel. They can't - they're not big enough and they need to be fast and manueuverable, impossible if you're got a heavy fuel load.

Passenger jets, on the other hand, are big and designed to travel long distances - hence they carry huge amounts of fuel.

Also, the steel was weakened by the building fire touched off by the initial explosion and the building structure severely damanged by the impact of the plane.