NORAD, responsible for intercepting errant aircraft over the U.S., has a standard operating procedure for scrambling planes for interception which takes less than 15 minutes

They did this successfully (on time) 129 times in 2000 and and 67 times between September 2000 and June 2001.

Yet, on September 11th, they failed to do their job 4 times in a single day:

NORAD, once notified of the off-course aircraft, failed to scramble jets from the nearest bases

Once airborne, interceptors failed to reach their targets because they flew at small fractions of their top speeds

Fighters that were airborne and within interception range of the deviating aircraft were not redeployed to pursue them

ordered

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