Continuity: 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.

Factual error: The emergency exits on the inside of the Boeing 757 are designed for a Boeing 747 not a 757. If you look closely the doors are not armed either, which they would be on a passenger jetliner so the slides could deploy if the plane crashed.

Continuity: At the end, during the fight scenes in the first class cabin, the number of overhead compartment doors that are open changes.

Continuity: United 93 is cleared to depart from runway 4L at Newark. However, you can see the terminals out the right side of the aircraft, indicating that it is departing to the southwest, on runway 22R.

Continuity: When United 93 is in the air, the terrorist in the back of the plane has his brown jacket alternately zipped/unzipped between shots.

Factual error: During the take off roll, the curtain that divides First Class and Economy class is closed. This is in breach of FAA regulations that state the curtain must be stowed for taxi, take-off and landing.

Factual error: In an early runway scene, a billboard for the film Chicken Little (2005) can be seen in the background.

Deliberate "mistake": After takeoff, an exterior shot of the plane switches from a Boeing 757 to an Airbus A320.

Continuity: Shortly after take off from Newark the plane has changed from a Boeing 757 to an Airbus plane as evidenced by the design of the winglets.

Factual error: In one of the shots when the 757 is taxiing at Newark airport, you can see in the background an airliner in the new Air Canada colours. The current Air Canada livery was introduced in 2004.

Factual error: The UPS airplane shown on the tarmac at Newark Airport is painted with UPS's new logo, which was not introduced until 2003.

Deliberate "mistake": In the beginning of the movie when the United pilots are walking toward the plane they show United 93 at its gate. The plane shown is a Boeing 777 and not the 757-222.

Continuity: In the Boston ATC sequence, the radar screen shows American 11 at a flight level of 350 (35,000 ft) this alternates with a flight level of 310 between shots.

Continuity: Throughout the film if you look at the terrorist that wears the black polo shirt with the lines across it, the red bandanna keeps changing position, from thin and covered in hair, to thick with no hair covering.

Audio problem: When auditing the recording of one of the first hijacks, the FAA reviewer rotates the tape reels back and forth in order to find just the exact words from the hijacker. As the sounds play, the reel moves barely half a turn, but the reviewer rewinds it more than one revolution, not nearly returning to where that sound would be.

Continuity: In the beginning of the movie, when we see a hurried passenger trying to get through the security check, he takes his pocket change out of his pocket and puts it on top of the scanner. In the next shot, the money is gone and there's a purple tray instead.

Continuity: During the hijack, a female passenger goes to help another one who has been stabbed in the neck, bleeding profusely. When she returns to her seat, she has no blood on her.

Factual error: In a scene in New York's air traffic control tower (I think the one where they show the second plane hit the south tower of the WTC), there is a man wearing a black lanyard around his neck that says "Transportation Security Administration" on it. The TSA was formed shortly AFTER the events of 9/11 thus he should not be wearing it.