It is the enormous amount of fuel that they carry. In a crash it doesnt take much to create a spark and its all over. You will note that lower speed crashes dont always explode. The aircraft chosen for 9/11 were on long distance routes and had just taken off - therefore maximum fuel on board.
Airplanes don't necessarily blow up when they crash. If they are carrying large amounts of fuel, the fuel may catch fire or explode, but that is by no means a universal occurrence.
Airplanes that crash-land fairly smoothly may not experience any explosion or even any fire. This is also true for airplanes that are out of fuel or have very little fuel remaining on board.
Airplanes that crash catch fire and/or explode for much the same reasons that a car or other vehicle might explode or catch fire in a crash. It's almost always a question of fuel.
This is due to the fuel they are carrying.
Depends on the impact, if its enough to tarnish the tanks.
They don't always. The messier ones get the most 'press'.
We try to design them not to, but hot engines, active electrical circuits,
and a light structure containing a lot of fuel makes it hard to do.
they carry over 9000 gallons of fuel
uh because of the several thousand pounds of fuel they carry