To see how much the Sept. 11th attacks affected people's flight behavior, I examined some publically available data about the number of miles traveled by airplane and US GDP. See the figure below.

People flew more and more miles through the late 90’s and until the 9/11 attacks. The number of miles traveled dropped precipitously immediately after the attacks, probably due to the emotional reaction and negative association with the airlines. But the recovery was fairly quick. By 2005, the number of miles flown reached not only the levels before the attacks, but the levels expected given the slow steady increase observed through the late 90’s and ’00 – ’01.

After 2005, it seems the number of miles traveled began to steady. Then, around the time the recession hit, it fell again, even when controlling for GDP and has remained steady since.