"Nobody has ever test flown a 767 that fast to see what would happen. The Vd airspeed on a Vn/Vg diagram is a "design dive" airspeed, which the engineers use to spec out the airplane's parts (to some factor of safety above the dynamic pressures at that airspeed). And then they go flight test it. They test it to that speed, and call it good. They do not go faster and faster until something breaks to see when that happens. All we can say for sure is that at airspeeds outside the design and test envelope, the airplane's performance is no longer guaranteed. That does not mean that a 767 will explode at Vd + 1 knot, merely that the engineers can no longer promise that everything will stay together up to their specs. We can speculate that parts will probably come off as we go faster and faster, but we have absolutely no idea at what airspeed that happens. 9/11 conspiracy theories like this are literally unfalsifiable, because we have no data to indicate if a 767 is able to stay together at such high airspeeds. But we also have no data to indicate that a 767 cannot stay together at very high speeds. All we know for sure is that a 767 will be okay at a lower airspeed. In some way, your opinion of what happens to a 767 at high airspeed depends on your opinion of 9/11. If you're like me, 9/11 shows that a 767 can be flown at some speed faster than it was ever tested. If you're a truther, a 767 doing so is evidence of a vast conspiracy."