People forget how the WTC was built. Normally skyscrapers are built with an internal framework which the floors are attached to. But to maximize the office space, the WTC was built like a tube with all the strength on the outside, and a framework hung from the inner side of the outer walls. Go pull the tube out of a roll of paper towels. As long as the tube is unbroken, it will support a great deal of weight, against the force of gravity. Now take a pair of scissors and cut the tube. You'll find that the tube can support almost no weight at all. When the plane crashed into those particular buildings, they destroyed the structural integrity of the outside load bearing walls. Then gravity takes over. And in this universe gravity pretty much always wins in the end. with the walls weakened, the WTC could no longer bear the weight of the upper floors down it comes, and as the floors pancake down, even more weight is accelerating into the floors below. BTW., on the skill of the pilots; isn't it true that more piloting skill is necessary to fly a small plane, whereas in a jumbo jet, much of the work is done by computers?
