Beginning 14 months before the hijackings, several of the terrorists take flight training courses. They acquire flight deck videos for Boeing 747, 757, 767, and 777 aircraft.1

1 Goldberg, A. Papadopoulous, S., et al “Pentagon 9/11” Historical Office, Office of the Secretary of Defense n.d PDF. March 16, 2011 page 9 http://osdhistory.defense.gov/docs/Pentagon%209-11.pdf