On September 11, America’s air defense depended on close interaction between the Federal Aviation Administration (FAA) and the North American Aerospace Defense Command (NORAD).  The FAA is mandated by law to control the safety and security of civil aviation.    Typically that meant maintaining a safe distance between aircraft.  NORAD was established in 1958 between the United States and Canada.  It was created to counter the threat of Soviet bombers and its mission was to defend the airspace of North America and protect the continent.  NORAD reached a high of 26 alert sites, but with the end of the Cold War the number of alert sites was continually reduced, and by 9/11 there were only seven alert sites left.  On 9/11, NORAD’s air defense mission was to “destroy, nullify, or reduce the effectiveness of attacking enemy aircraft or missiles.”  

In 2001, in the continental United States, NORAD was divided into three sectors.  All four of the aircraft hijacked on the morning of September 11, 2001, were in the Northeast Air Defense Sector (NEADS), which is based in Rome, New York.  On call that morning for NEADS were two alert sites, each with one pair of fighter jets:  two F-15s from Otis Air National Guard Base in Cape Cod, Massachusetts, and two F-16s from Langley Air Force Base in Hampton, Virginia. 

The FAA and NORAD had developed procedures to be implemented in the event of a hijacking that required the FAA to go through multiple levels to obtain approval for military assistance.  If a hijacking was confirmed, the FAA would contact the Pentagon’s National Military Command Center (NMCC) and ask for a military aircraft to follow the flight.  The NMCC would then seek approval from the office of the Secretary of Defense.  If approval was given, NORAD would be notified and the FAA center that was tracking the hijacked aircraft would then be authorized to coordinate the military response with NEADS.  The many levels within the military that required notification and approval made this process a very time-consuming event.  After gaining approval, the FAA would provide NEADS with the hijacked aircraft’s call sign, position in latitude and longitude, heading, airspeed, and altitude.  Normal procedures for fighter aircraft launched in the event of a hijacking did not include an intercept of the hijacked aircraft.  Instead, the fighter escort would not make its presence known but would be vectored to a position five miles behind the hijacked aircraft. 

Before September 11, 2001, there were three key presumptions regarding what a hijacked aircraft would do.  First, the aircraft would be easy to identify and would not try to disappear from FAA controllers’ screens. Controllers track aircraft primarily by watching the data from a signal transmitted by an aircraft’s transponder radio. Commercial aircraft are given a unique four digit code to input into the transponder that allows controllers to track each aircraft.  It provides the identity of the aircraft by its call sign and gives the plane’s position and altitude.  This in turn helps the controllers to maintain vertical and horizontal separation of aircraft.

On 9/11, three of the four aircraft had their transponders turned off and another had its transponder code changed by the terrorists.  American Airlines Flight 11 had its transponder turned off at 8:21.  At 8:47, the four digit transponder code on United Airlines Flight 175 was changed and then changed again.  The change wasn’t noted until 8:51, and after several minutes of trying to contact United 175 the controller reported he could not find the aircraft.  American Airlines Flight 77 had its transponder turned off at 8:56 and the transponder of United Airlines Flight 93 was turned off at 9:41.  With the transponder turned off it was still possible, though more difficult, to track the aircraft through primary radar.  Primary radar returns take a signal sent from a radar site and bounces it off an object in the sky.  It will not include the aircraft’s identity and altitude.  Air traffic control would have to search their radar screens with thousands of identical radar blips crossing through some of the nation’s busiest air corridors.  In addition, pre- 9/11, NORAD did not view flights originating within the United States as a threat so their radar was focused outward.  This also added to the difficulty in identifying the hijacked aircraft.   

The second presumption was that there would be time for the FAA to follow the protocol to request assistance through NORAD and still allow time to launch aircraft.  In addition, it was assumed that an aircraft being hijacked would notify air traffic control either by making a radio call or by inputting a code of “7500”, the universal code of “hijack in progress,” into the transponder radio.  This would not only alert air traffic control that the aircraft was declaring an emergency due to a hijacking, but would identify which aircraft it was and provide a current position and altitude.  The greatest amount of notification the military received on 9/11 from the FAA of any of the four hijacked airplanes was nine minutes prior to the first hijacked aircraft, American 11, being flown into the North Tower of the World Trade Center at 8:46:40.  NEADS received notification of the second hijacked aircraft, United 175, as it struck the South Tower of the World Trade Center at 9:03:02.  There was no notification that American 77 had been hijacked prior to its being flown into the Pentagon at 9:37:46.  NEADS was notified that United 93 was hijacked four minutes after it had crashed in Shanksville, Pennsylvania at 10:03:11. 

The third presumption was that the hijacking would be traditional and not a suicide designed to use the aircraft as a weapon.  Of the three pre-9/11 presumptions, this was the most problematic. It is possible that air traffic control may have been able to identify the hijacked aircraft even though the transponder had been turned off by using primary radar.  Additionally, one of the alert sites might have been close enough to allow the fighter jets enough time to launch and then shadow the hijacked aircraft.  But even if there had been time for the fighter jets to discern the hijacked aircraft were on a suicide mission, they did not launch with standing orders to shoot them down.  Prior to 9/11, it was understood that an order to shoot down a commercial aircraft would have to be issued by the National Command Authority (NCA).  The NCA consists of the President and the Secretary of Defense or their duly deputized alternates or successors.  Absent a presidential directive, these fighter jets had no authority to shoot a commercial airliner out of the sky.  The time that the order was given that authorized the shooting down of the hijacked aircraft is not exactly clear.  However, what is clear is that the military pilots had no orders until after all four aircraft had crashed.  

America’s air defense system was unprepared for the type of attack that occurred on 9/11.  The procedures in place on September 11 required close interaction between the FAA and NORAD and assumed a “classic” hijacking scenario: ample notification time, no difficulty in locating the aircraft, hijackers intending to land the aircraft, and military aircraft limited to escort.  What they had trained for was not what they encountered.  As the 9/11 Commission concludes, NORAD and the FAA “struggled, under difficult circumstances, to improvise a homeland defense against an unprecedented challenge they had never before encountered and had never trained to meet.”

The 9/11 Commission goes on to state that though NORAD officials have maintained that they would have intercepted and shot down United 93, Commission staffers are not so sure.  “The nation owes a debt to the passengers of United 93.  Their actions saved the lives of countess others, and may have saved either the Capitol or the White House from destruction.” As an assistant to the mission crew commander observed while working on the floor of the NEADS command center on 9/11, “This is a new type of war.”