Have you never done the research on this subject...? The US Air Force fighter planes were ordered to remain in a holding pattern and were not dispatched because...coincidentally, there was a major military exercise taking place at the same time...involving commercial aircraft being hijacked over American airspace. So, as the story goes, the military was simply following the "rules of engagement" for the military exercise, essentially indicating that this was the root cause of confusion that resulted in the delayed response of armed aircraft.