September 11, 2001: Flight 11 Transponder Turned Off

[Archangel]

Shortly after air traffic controllers ask Flight 11 to climb to 35,000 feet, its transponder stops transmitting. A transponder is an electronic device that identifies a plane on a controller's screen and gives its exact location and altitude. Among other vital functions, it is also used to transmit a four-digit emergency hijack code. Flight control manager Glenn Michael later says, "We considered it at that time to be a possible hijacking." [Christian Science Monitor, 9/13/2001; MSNBC, 9/15/2001; Associated Press, 8/12/2002]

Initial stories after 9/11 suggest the transponder is turned off around 8:13 a.m., but Pete Zalewski, the air traffic controller handling the flight, later says the transponder is turned off at 8:20 a.m. [MSNBC, 9/11/2002]

The 9/11 Commission places it at 8:21 a.m. [9/11 Commission, 6/17/2004] Colonel Robert Marr, head of NEADS, claims the transponder is turned off some time after 8:30 a.m. where the Flight 11 hijack was first detected a.m. [ABC News, 9/11/2002]