10:02 a.m. September 11, 2001: Flight 93’s Transponder Briefly Comes Back On

Flight 93’s transponder, which was switched off after Flight 93 was hijacked, is turned back on just before the plane crashes, thereby revealing the plane’s altitude to air traffic controllers at the FAA’s Cleveland Center. [Federal Bureau of Investigation, 9/11/2001; MSNBC, 9/11/2002] A transponder is a device that sends a plane’s identifying information, speed, and altitude to controllers’ radar screens. [Washington Post, 9/16/2001] Flight 93’s transponder was switched off at around 9:40 a.m. (see (9:40 a.m.) September 11, 2001), although Cleveland Center controllers have still been able to follow Flight 93 on “primary radar,” which shows less information about a flight (see (9:41 a.m.-10:06 a.m.) September 11, 2001). [Federal Bureau of Investigation, 1/8/2002; 9/11 Commission, 7/24/2004, pp. 29; Cleveland Plain Dealer, 7/3/2011]
Plane Shown to Be Flying at 8,200 Feet – Flight 93’s transponder is reactivated at 10:02 a.m. and 50 seconds, and then stays on for “approximately 20 seconds,” according to “information from the flight data” provided to the FBI later today by Rick Kettell, the manager of the Cleveland Center. After the transponder is turned back on, Flight 93’s radar track is observed by Cleveland Center controllers Linda Justice and Stacey Taylor. The information from the transponder shows them that Flight 93 is at an altitude of 8,200 feet. [Federal Bureau of Investigation, 9/11/2001; Federal Aviation Administration, 9/16/2001 ; 9/11 Commission, 10/2/2003 ]
Plane Soon Disappears from Radar Screens – Flight 93 will crash into the ground at 10:03 a.m. and 11 seconds, according to the 9/11 Commission Report, less than 30 seconds after the transponder is reactivated (see (10:03 a.m.-10:10 a.m.) September 11, 2001). [9/11 Commission, 7/24/2004, pp. 30] Cleveland Center controllers will see the plane completely disappear from their radar screens around that time. [MSNBC, 9/11/2002] A Cleveland Center controller will then report, apparently over an FAA teleconference, that Flight 93’s transponder “came on briefly and then it went back off with the primary, and now we’ve lost him completely.” [Federal Aviation Administration, 9/11/2001] “I had two radar hits on [Flight 93],” Taylor will recall, adding that she then “lost the primary target on [Flight 93] and we suspected it had gone down.” [Federal Aviation Administration, 9/16/2001 ] The reason Flight 93’s transponder is switched back on just before the plane crashes is unclear. Taylor will comment, a year after 9/11: “That’s something we’ve always wanted to know. Why did the transponder come back on?” She will say Cleveland Center controllers wondered this because they believed that “the hijackers had shut it off so that they couldn’t be tracked.” [MSNBC, 9/11/2002]