Phil MolĂ© of Skeptic magazine has explained that it is neither quick nor easy to locate and intercept a plane behaving erratically, and that the hijackers turned off or disabled the onboard radar transponders. Without these transponder signals to identify the airplanes, the hijacked airplanes would have been only blips among 4,500 other blips on NORADâ??S radar screens, making them very difficult to track.[69][72]

According to Popular Mechanics, only 14 fighter jets were on alert in the contiguous 48 states on 9/11. There was no automated method for the civilian air traffic controllers to alert NORAD.[72] A passenger airline had not been hijacked in the US since 1979.[75] "They had to pick up the phone and literally dial us," says Maj. Douglas Martin, public affairs officer for NORAD. According to Popular Mechanics, only one civilian plane was intercepted in the decade prior to 9/11, which took 1 hour and 22 minutes.[72]

Rules in effect at that time, and on 9/11, barred supersonic flight on intercepts. Before 9/11, all other NORAD interceptions were limited to offshore Air Defense Identification Zones (ADIZ). "Until 9/11 there was no domestic ADIZ," says FAA spokesman Bill Schumann. After 9/11, the FAA and NORAD increased cooperation. They set up hotlines between command centers while NORAD increased its fighter coverage and installed radar to watch airspace over the continent.[72