A NORAD training exercise that is taking place this morning, presumably Vigilant Guardian (see (6:30 a.m.) September 11, 2001), is reportedly canceled shortly after 9:03, when the second World Trade Center tower is hit. [Airman, 3/2002] NORAD Commander Larry Arnold later says that after Flight 175 hits the South Tower, “I thought it might be prudent to pull out of the exercise, which we did.” [Filson, 2003, pp. 59] According to author Lynn Spencer: “The phone calls start flying between the various NORAD command centers. General Arnold calls Maj. Gen. Rick Findley” at NORAD’s operations center in Cheyenne Mountain, Colorado, “to give him the latest information and have him withdraw all forces from the simulated exercise.” [Spencer, 2008, pp. 86] Arnold will recall, “As we pulled out of the exercise we were getting calls about United Flight 93 and we were worried about that.” [Filson, 2003, pp. 59] Some early accounts say the military receives notification of the possible hijacking of Flight 93 at around 9:16 a.m. (see 9:16 a.m. September 11, 2001). [CNN, 9/17/2001; 9/11 Commission, 5/23/2003] However, the 9/11 Commission will later claim that NORAD’s Northeast Air Defense Sector (NEADS) first receives a call about Flight 93 at 10:07 a.m. (see 10:05 a.m.-10:08 a.m. September 11, 2001). [9/11 Commission, 6/17/2004 ] Arnold will add, “Then we had another call from Boston Center about a possible hijacking, but that turned out to be the airplane that had already hit the South Tower but we didn’t know that at the time.” [Filson, 2003, pp. 59]