9:55 a.m. and After September 11, 2001: Numerous International Flights to US Transmit Emergency Transponder Codes

FAA radar displays begin showing that a growing number of international flights approaching America are transmitting warning codes from their transponders. [Spencer, 2008, pp. 196-197]
Airspace Shut Down – At around 9:45 a.m., the FAA shut down US airspace and ordered all aircraft to land (see (9:45 a.m.) September 11, 2001). Shortly afterwards, Canada took similar action. However, international flights that are over the oceans and approaching America are getting low on fuel. As their crews establish radio contact with air traffic controllers, they are told that American airspace is closed. Many of the worried pilots dial emergency codes into their transponders. [US Congress. House. Committee On Transportation And Infrastructure, 9/21/2001; 9/11 Commission, 7/24/2004, pp. 29; Spencer, 2008, pp. 196]
Radar Screens Highlight Numerous Flights – A plane’s transponder is a device that sends that aircraft’s identifying information, speed, and altitude to radar screens. [Washington Post, 9/16/2001] There are three specific codes that pilots can dial into their transponder to signal an emergency: “7500” signifies a hijacking, “7600” signifies a loss of radio, and “7700” signifies other emergencies. [Spencer, 2008, pp. 25-26] Amid the current crisis, FAA radar screens begin highlighting a growing number of flights over the oceans that are transmitting warning codes. According to author Lynn Spencer, “One foreign crew dials in the four-digit code for ‘hijack,’ just to let the authorities know they are aware of what is taking place.” [Spencer, 2008, pp. 196-197] In response to a request from the FAA, Canada will agree to open its airspace to all international flights that are diverted away from the United States, allowing those flights to land at Canadian airports (see 10:21 a.m. September 11, 2001). [CNN, 9/12/2001; Time, 9/14/2001; NAV Canada, 7/22/2005]