Perhaps it could have been hit by a 707 and survive. But planes got much bigger since then
Perhaps it could have been hit by a 707 and survive. But planes got much bigger since then.Actually, they have. The 707 had a 130' wingspan and a gross weight of 80 tons.
The 767-400 (the largest 767 variant) has a wingspan of 170' and a maximum weight of 225 tons. The 767-200 has a wingspan of 156' and a maximum weight just under 200 tons.
Also, the building stood up to the impact of the 767. It was the fire damage that caused the building to collapse. I'm pretty sure that the engineers that claimed it could take an impact from a 707 weren't considering the effects of the resulting fire. If the airlines still flew 707's, one of those would probably have done the job.
I'm pretty sure that destroying the buildings was the goal of these terrorists. However, I'm not convinced that they did that much engineering and analysis. It's entirely possible that they went with "Well, a bomb in the basement didn't do it, let's try a big airplane in the side."
Even if they didn't completely destroy the buildings, this was still would have been a successfull terrorist strike. They would have killed all the passengers on both planes and also most of the people on the floors that they hit directly. They picked planes that were bigger than the public claims of the engineers. They probably figured that they would do enough damage to make the buildings unusable (and possibly unrepairable) for a long time. Actually, if they wanted a monument to their attack, they probably would have preferred the big hulking, uninhabitable wreckage to stay standing.
I agree that they picked their flights carefully, choosing planes that would have been fully loaded with fuel. But this doesn't take any particular engineering skill. It's pretty obvious that a flight from Boston to San Francisco would have more fuel aboard than a flight from Boston to Washington DC.
Also, I saw some radar traces on one of the networks last night. I wasn't impressed with the navigation skills and flying skills of these "pilots." It looked to me like strictly a VFR type approach. You can see New York City and especially the World Trade Center towers from a very long way away. I don't think they used any of the navigation tools available to them. They more likely turned and pointed the plane at the target visually.
Also, the speed variations and altitude wierdness also makes it look like these "pilots" weren't very well trained. Possibly just some PC based flight simulator time plus some time looking at pictures in those flight training manuals they apparently had. I'm not saying they might not have had more skills, but those are the minimal skills required to do what they did.