In the event of a hijacking, all airline pilots are trained to key an emergency four-digit code into their plane’s transponder. This would surreptitiously alert air traffic controllers, causing the letters “HJCK” to appear on their screens. [CNN, 9/13/2001; Newsday, 9/13/2001; News (Portugal), 8/3/2002; 9/11 Commission, 7/24/2004, pp. 17-18] The action, which pilots should take the moment a hijack situation is known, only takes seconds to perform. [Christian Science Monitor, 9/12/2001; CNN, 9/12/2001] Yet during the hijackings of flights 11, 175, 77, and 93, none of the pilots do this. [CNN, 9/11/2001]