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.
During the overview of the Newark airport in the beginning, an air traffic controller wears a blue lanyard that says "Transportation Security Administration," with an American flag dafter "Transportation". The Transportation Security Administration was formed under the Aviation and Transportation Security Act, which was signed into law on November 19, 2001. Most 2001 roll-out supervisors at TSA have these lanyards for airport identification cards. An ATC could own a lanyard, as it is understandable that the lanyards would be distributed among airport operations personnel.
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.
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.
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.
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.
Near the end, when the passengers are fighting for control of the plane, the main flight attendant appears in many shots as the passengers move to the front. Her hair is different in almost every shot.
Once the passengers on the plane are hear about the World Trade Center attacks, the flight attendants at the back start hearing the passengers talking and start reacting. However, the flight attendants' positions change very noticeably between shots. One is in front of the rest of the flight attendants at the back listening to the passengers, then in the far corner, tucked up against the door of the plane hiding. In the next shot, she's back to her original position.
When the hijacker rolls the plane to knock the passengers off balance, one of the flight attendants falls to the floor at the rear of the plane. In the next shot, she struggles to get up in first class. A few scenes later, she is back at the rear of the plane, getting up.
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.
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.
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.
During first officer's pre-flight walk around, the aircraft has Rolls-Royce RB211 engines. In exterior shots, the planes engines alternate between Rolls Royce and Pratt & Whitney. All United 757's have two distinctive Pratt & Whitney 2040 engines.
In the beginning, when both pilots are walking to aircraft, First Officer LeRoy Homer says that he lives about an hour north of Newark. Homer lived in Marlton, New Jersey, a Philadelphia suburb about a 90 minute drive south of Newark.
Boston Air Traffic Control Center refers to American Airlines flight 11 and United Airlines flight 175 as 'American eleven' and 'United one seventy-five.' New York Air Traffic Control Center refers to the United flight with 'heavy' succeeding the call-sign, even though both planes are Boeing 767-200s.
In the film, Marion R. Britton hands her cell phone to fellow passenger Honor Elizabeth Waino before the passengers try to take back the plane. In real life, Lauren Grandcolas gave Waino her phone so she could call her mother.
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.