After 10:00 a.m. September 11, 2001: Plane Heading for Britain Appears Suspicious, Emits Strange Transponder Signals

CIA Director George Tenet later recalls that, at some unspecified time during this day, a commercial passenger jet on its way to Britain behaves suspiciously, raising fears that al-Qaeda might have launched a two-continent attack. Aircraft are equipped with a device called a transponder, which transmits information to controllers on the ground, such as the plane’s flight number, altitude and speed. But this plane is emitting all kinds of “squawks,” with its transponder going off and on. Tenet calls Richard Dearlove, his counterpart at the British Secret Intelligence Service (MI6), to inform him of what is going on. Eventually, according to Tenet, the problem is resolved, and it turns out to have been caused simply by the transponder being faulty. [Washington Post, 9/17/2001; Tenet, 2007, pp. 166]