Tape recordings of the operations floor at NORAD’s Northeast Air Defense Sector (NEADS) indicate that some military personnel are uncertain whether a training exercise that was being conducted on this day has been canceled. NEADS has been participating in a major exercise called Vigilant Guardian. [Newhouse News Service, 1/25/2002] This was reportedly called off “shortly after” the second WTC tower was hit at 9:03 (see (Shortly After 9:03 a.m.) September 11, 2001). [Airman, 3/2002] But at 10:06, someone calls NEADS and asks, “Is the exercise knocked off?” to which they are told, “Yes.” Two minutes later, a member of the NEADS staff is heard saying, “If this is an exercise input, this is a good one.” [North American Aerospace Defense Command, 9/11/2001] It is around this time that NEADS is first alerted to Flight 93 (although this plane has already crashed) (see 10:05 a.m.-10:08 a.m. September 11, 2001) and also hears a report of an unidentified aircraft over the White House (see 10:07 a.m. September 11, 2001). So presumably it is one of these incidents that is considered a possible “exercise input,” meaning a simulated scenario. [Vanity Fair, 8/1/2006]


