When the last passenger rushes to make the plane, the metal detector goes off. He throws a lot of loose change on the Rontgen scanning machine. When cleared, he picks up his bag and his belongings but the coins have disappeared from the machine and he hasn't taken them.
When the last passenger is boarding the plane you can see the blue curtain dividing the two classes is closed, but just a second after you can see the passenger entering coach class with the curtain open.
When the hijacker attacks the flight attendant Lorraine Bay when the hijacking occurs, we see him with his hand around her neck in the middle of the plane. When the hijackers are threatening the passengers and telling them to sit down and be quiet, you can see the actress who is playing Lorraine Bay in the back of the plane standing up. When the camera comes back to the hijacker in the middle of the plane, the actress playing Lorraine is still being held by him.
At one point, a radar screen shows "CLE" and an airport diagram, meaning Cleveland Hopkins International Airport. The runway diagram is incorrect for the airport; it shows a triangle, while Hopkins Airport's runways form a slanted "T" shape.
On the ramp area we see that United 93 aircraft is being pushed back by a Servisair/Globeground (now Penauille Servisair) push-back machine. For pushing back and ground services United Airlines uses United Services (a parent company).
in this movie you can see the actresses portraying flight attendants Wanda Green and Cee Cee Lyles in the opposite classes of service. on the real life flight Wanda was serving first class while Cee Cee was back in economy.
When flight 93 is going nose down, and you can see the ground approaching through the cockpit wind shield, the flight instruments (most notably the horizontal situation indicators and attitude indicators) show business as usual - that is, the plane is flying more or less horizontally, which doesn't correspond with the fact that they are about to crash.
In the scene where the fighter pilots are advised that the plane went down, the jet in the background takes off and the camera stays on the other jet. In the cockpit, you can see that fighter pilot waving at the camera.
While United 93 is still on the apron, in one shot, you can clearly see a WestJet 737-700 in the background, which, in the very next shot, is taxiing behind United 93 for departure. Westjet does not serve Newark New Jersey, and WestJet Airlines did not add Transborder service to the United States until 2004, therefore, that plane should not have been there.
In closeup shots of the F-16 pilot talking to the controller, there is a windshield frame visible in front of him. The F-16 is unique in that it has a canopy with a one large piece incorporating the windshield and extending to behind the seat, and a separate smaller section at the rear of the cockpit.