Continuity mistake: After the hijackers have taken over the plane, the blond flight attendant's hair, styled in a French Twist, keeps changing from messy (presumably from the chaos) to as smooth and neat as when she boarded the plane. She's never offscreen long enough to have simply fixed it. Not until the passengers revolt does it remain disheveled.
Trivia: Families of the 40 passengers and crew members killed on United Flight 93 cooperated in the production, offering Greengrass detailed background about their loved ones, down to the clothes they wore, what reading materials or music they had with them and what sort of candy they might have snacked on aboard the plane.
Trivia: The FAA National Operations Manager, Ben Sliney, was played by himself. September 11/2001 was also his first day on the job.
Question: How come the terrorists' knives were not noticed? Airports have metal detectors designed to detect knives.
Question: I know this has nothing to do with movie's plot, but I'm going to ask it anyway. How did the hijackers know that destroying the twin towers would affect the US economy?