AOPA sponsors its own Fly-In and open house in Frederick Maryland . The yearly event started in 1991 with 125 aircraft . By 2001 , the attendance grew to 760 aircraft . The event was cancelled for five years after the September 11 , 2001 attacks and consequent airspace changes , but resumed in 2006
September 11 , 2001 attacks
September 11 attacks
Aircraft Owners and Pilots Association