Additionally, in my experience as an officer in NORAD as a Tactical Director for the Chicago-Milwaukee Air Defense and as a current private pilot, there is no way that an aircraft on instrument flight plans (all commercial flights are IFR) would not be intercepted when they deviate from their flight plan, turn off their transponders, or stop communication with Air Traffic Control. No way! With very bad luck, perhaps one could slip by, but no there's no way all four of them could!
Absolute fucking nonsense everyone of those planes except perhaps the one in Pensylvania had impacted their targets within ten minutes of take off. Even at alert status it take you longer than that to scramble the fighters and find the damn targets.