But go ahead, believe Howlin. She's always 1000% right.
But it wasn't in the first few days; and they didn't leave before the ban was lifted:
Sept. 13 Secretary of State Colin Powell identifies bin Laden as prime suspect. Limited commercial flights resume. National Football League, major-league baseball call off weekend games.
"At the least September 14th through the 19th. While the national airspace was officially closed."
National airspace was re-opened partially on September 14th and completely on September 15th. I remember. I was manufacturing Boeing commercial airplanes at the time and it was very important how long national airspace was closed. I also remember thinking that it may have been opened too soon considering what had just happened.