A 9/11 Commission record released to the National Archives summarizes 28 NORAD exercise scenarios in the 3 years prior to 9/11 which involved hijacking. Many involved intercept/shadowing by fighter jets, at least 2 involved planes crashing into cities/buildings, & at least 3 involved shoot-downs, including a version of Vigilant Guardian in Oct 98.
Two Days Before 9/11, Military Exercise Simulated Suicide Hijack Targeting New York http://hcgroups.wordpress.com/2009/06/14/two-days-...
The US military conducted a training exercise in the five days before the September 11 attacks that included simulated aircraft hijackings by terrorists, according to a 9/11 Commission document recently found in the US National Archives. In one of the scenarios, implemented on September 9, terrorists hijacked a London to New York flight, planning to blow it up with explosives over New York.
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