On Oct 1999 Payne Stewart's private jet lost pressure at 24000 ft and everyone passed out on his flight from Florida to Texas. When ATC detected his jet going off course NORAD was contacted and within 2.5 minutes a NORAD F16 was on Stewart's wingtip trying to look into the cockpit of the frosted up windows. The private jet was followed north for 4 hours. 6 x F16's followed it in relay. There was an emergency meeting of the Joint Chiefs of Staff at the pentagon in teleconference with the White House.

On 9/11 none of this happened in the busiest and most closely surveilled air traffic corridor in the world as 4 planes were hijacked and flew far off course for an hour and forty minutes even after the first two planes crashed. No response from NORAD at all

https://youtu.be/x109izx4qIA [Embed]

It is impossible that NORAD should not have responded immediately across the board to this threat.