Well, you've managed to mis-apply Newton's Law, for starters.  Your conclusion is nuts.  The mass of the building is far greater than the mass of the airplane, and that makes a big difference in the calculation of momentum. And jet planes can travel easily at 500 mph at low altitude, though that is not their normal operating condition.  (At least one 727 survived a vertical dive that went supersonic.) Which gives me a clue as to how well you have been studying the facts.