After takeoff, an exterior shot of the plane switches from a Boeing 757 to an Airbus A320.
In the beginning, when the hijackers are leaving their hotel room, the one in the front is wearing a horizontally striped polo shirt. In the next shot, as they are walking down the hallway, the same man is now wearing a button-down shirt and a sport coat.
After the hijackers arrive at the airport, Saeed al-Ghamdi enters the terminal twice.
When the captain turns off the fasten seat-belt sign, the flight attendant walks through the closed curtain, turns and closes it again, says her line at the front of the plane, and turns back towards the curtain, which is now fully open.
The hijacker flying the plane puts it into a steep dive. When the camera shows the passenger cabin, the plane appears to be angled upwards as if in a steep climb. The hijacker watching the passengers from near first class leans backwards, towards the cockpit, to maintain his balance, also indicating a climbing deck angle.
A number of passengers make phone calls from cell phones. In real life, only two people made calls from cell phones during the last few minutes of the flight: Edward Felt and CeeCee Ross Lyles. All other calls came from in-flight Airphones.
In the film, only two hijackers, Saeed al-Ghamdi and Ahmed al-Nami, wear red bandannas. In real life, all four hijackers wore red bandannas when United 93 was hijacked.
In the film, the terrorists in the cockpit communicate in Arabic. In real life, they spoke English when the passengers tried to take back the plane.
The hijackers in the film have very notable North African and Iraqi accents. In real life, the hijackers were Saudi and Lebanese, with very different accents.
Towards the end, the passengers successfully kill Ahmed Al-Haznawi and Ahmed Al-Nami before they break into the cockpit, then fight Saeed Al-Ghamdi and Ziad Jarrah over the controls just as the plane is about to crash. In real life, it is assumed that three hijackers were in the cockpit, and the hijacker who was outside the cockpit was killed.
Shortly after the cockpit takeover, one shot of the fuel indicator shows that the tanks are empty.
When the hijackers force the flight attendants to knock at the cockpit door, the little knife bends at a serious angle under one woman's chin, indicating that it's rubber.
As Flight 93 begins its takeoff roll, only one passenger seems affected by the acceleration.
In several scenes, the altitude indicator ("artificial horizon") shows the aircraft in a climb, while shots through the windscreen show the aircraft in a dive. The scene is shot at a downward angle, furthering the illusion of a dive.
When the terrorists first take over the plane they put it in a steep dive, however the ADI (Attitude Director Indicator) is showing the aircraft flying straight and level. Later the ADI follows what the action is showing.
The United logo at the gate was not in use in 2001.
The UPS plane on the Newark Airport tarmac has a post-2003 logo.
Near the beginning, a car arrives at the airport. A shot from the inside reveals an inspection sticker on the windshield that expires in 2004. The latest a 2001 inspection sticker could expire would have been 2002.
Early in the film, 375 Pearl Street is seen with the Verizon logo on it. That wasn't added until 2002. In 2001 it would have had the Bell Atlantic logo there instead.
Just before Captain Jason Dahl announces a delay in take-off, an Air Canada plane taxis behind Flight 93. It's an Embraer Jet, which the airline started flying in 2005, with a 2004 color scheme.
When auditing the recording of a transmission from American Airlines Flight 11, the reviewer repeatedly listens to the crucial portion, rewinds the tape, and listens again. The reel moves only a small fraction of a turn as the sounds play, while rewinding covers several times that distance, yet the reviewer always ends up at the same point in the recording.
During the final scene, when the cabin is inverted and the oxygen masks eject from the ceiling, some of the cabin ceiling panels are missing, revealing the set's light blue and red tubes and wires.
At the start of the movie, passengers arriving at the gate at Newark Airport are clearly at the domestic departure gates at Stansted Airport, Essex, UK. The scene includes BAA signage, seating at the gate (17), the rail link to the international departure gates (seen through the glass at the security checkpoint) and a "2 for £25" advertisement on the passenger walkway towards the gates.
The green "running man" EXIT signs in the terminal and jetway are used in the UK, not the USA.
Boston Air Route Traffic Control Center is in Nashua, New Hampshire, not Boston.
When United 93 enters Cleveland Air Traffic, it says Cleveland, Ohio. Cleveland Air Route Traffic Control Center is in Oberlin, Ohio, 35 miles southwest of Cleveland.
When Sliney is at the conference room at the FAA center in Virginia, a New York state flag is visible.
During take-off, the curtain that divides First Class and Economy is closed. FAA regulations state that the curtain must be stowed for taxi, take-off, and landing.