Factual error: When McClane lights the fuel with the zippo, the flame trail is all wrong. There appears to be a thin strip of fuel which accelerates away from him. However, we have seen the Fuel spurted out in a wider less controlled manner from a wing tip that has to be at least fifteen feet up, in a wind, which would have sprayed it around further. There is no way it would light in the tight manner shown. (01:45:55)
Continuity mistake: Col. Stewart asks if the 747 is ready and says he wants ground personnel to inspect the plane. Maj. Grant intercedes and tells Stewart to check out his own plane so not to have potential hostages (which, of course was a ploy). When the hanger door is opened, you see ground personnel running back and forth between the door. They are noticeable by their orange vests. (01:33:45 - 01:35:40)
Continuity mistake: In the beginning of the film when two of Stuart's men arrive at the church, their van stops and it is not snowing outside,same thing when they're shown knocking and then when the man opens the door. However, in the shot just after (which is taken from behind the door) snow is falling on them. The shot then switches to an outside view ,and it's not snowing anymore .
Deliberate mistake: At the very end, John McClane lights the fuel trail which subsequently engulfs the plane. To do this, he tosses a lighter onto the trail which begins six inches from where he lies, having fallen from the wing while pulling the lock off the fuel dumper. Trouble is, the fuel began flooding out at the same time he fell, and the velocity would carry him some distance forward on the ground after he lands (which it visibly does); hence, it is physically impossible for him to be in the position he is in relation to the fuel. (01:50:05)
Plot hole: When McClane gets kicked out of the control tower and is sent down in the elevator with Coleman he quite obviously stops the elevator before saying "Here's a couple of words, F**k off." to Coleman. He then opens the top panel and climbs out WITHOUT restarting the elevator. Almost as soon as he has closed the panel again the elevator has reached the bottom and the cops are asking "Where's the other one?" As it is meant to be a single shot and there is no delay we know Coleman did not start the elevator again herself. (00:38:25)
Factual error: There is absolutely no way the villains could remotely recalibrate the instruments on the plane itself. Even if it would be possible to remotely readjust the ILS glideslope - which it isn't - the pilot would've noticed their approach angle being suspiciously steep on the attitude indicator and the aircraft's radar altimeter would've given a terrain warning. (00:52:44)
Continuity mistake: While Barnes is brainstorming ideas with his staff about using the marker beacons to communicate with the circling planes, he has a pen in his right hand held to his face. The next shot he turns, but the pen is no longer in his hand and his hand is nowhere near his face.
Visible crew/equipment: When we first go to the Annex Skywalk, the SWAT team are walking with the guy from the tower and he is talking on a radio. In the mirror behind them you can see the boom mike and operator as they walk.
Factual error: In the tower, Leslie Barnes and a few men are talking about the Annex Skywalk, mentioning that it is a "VHF System." Barnes says the planes are so close it won't matter. VHF, or Very High Frequency, transmits far distances, hence why it is used by airports around the world. He should have said "UHF", which transmits shorter distances, as that would make more sense.
Continuity mistake: In the airport lobby, when the two policemen come at the bar they have "snow" all over their clothes. In the next shot they are shown from behind sitting at the bar and Lorenzo's brother has no snow on his jacket. Seconds after Mc Clane comes to talk to them and the cop has snow on his shoulders again.