[supercat]

I am wondering, how old were these planes that were used in the terrorist attacks?

Why does it matter? Break the sound barrier in a 757/767 and it will crash, regardless of its age. The stresses on the airframe at mach 1 are far beyond those experienced at 900fps. No matter how well built it may be, a plane which is not designed to survive the sound barrier, won't.

[Paul Atreides]

The reason I asked about the age of the plane is, aren't the airlines using some planes that are over thirty years old? I wasn't discounting the speed the plane was going at the time, nor was I discounting the stress being put on it. However, I was wondering if a plane that was over thirty years old, and has had more yearly wear on it than newer planes, might be more apt to break up more during the stress put on it during the struggle.