Factual error: It is impossible for a stream of burning jet fuel to follow a plane through snow and catch up. Not only is jet fuel extremely hard to ignite, almost as soon as the plane was off the ground the fuel stream would be too dispersed for the flame to climb up into the tank, and even if not it wouldn't burn fast enough to catch the plane.
Factual error: In circling over Washington Dulles, a plane would fly over several airports that they could land at with perfect communication, including Richmond, Baltimore, Andrews AFB, etc. Also, there is no communication from the airport to the plane but the plane would be in range of no fewer than 15 transmitting stations that could have relayed messages.
Plot hole: The only reason the terrorists' plot can work is that the airports around Dulles are all closed to landings because of the violent snowstorm. If there were no storm, the pilots of the airliners in the holding pattern would simply divert to nearby airports when they started running low on fuel. If they were able to do that, the whole plot would simply fall apart. How were the terrorists able to count on the storm happening on the very day General Esperanza's flight was due to land? They didn't have any influence over the date of his flight. How did they know the storm would be so bad that all airports would be closed - except Dulles? I don't think they had any way of predicting the weather quite that accurately, and If the storm hadn't hit or had been even slightly less severe the pilots of the stranded airliners could easily have diverted to any one of half a dozen alternate landing sites, including a nearby Air Force base. They could do this without consulting or even contacting air traffic control. The whole plot falls apart from there - no hostages, no leverage, and who cares what happens to the people on Esperanza's plane? They'd have it shot down as soon as they knew Esperanza had killed the pilot and taken over the flight.
Factual error: When McClane is trapped in the cockpit of Esperanza's plane, and the terrorists throw grenades in, it sure takes them a long time to explode, almost 30 seconds before he ejects from the plane and the grenades go off. Normal grenades have about a 5 second fuse. With a delay that long he could even have thrown them all back out at the bad guys.
Other mistake: The female journalist is called Samantha Coleman through the movie, but appears in the credits as Samantha Copeland.
Plot hole: When they try to contact the planes using the air phones, they say there are 18 planes but only 5 have airphones, and they got through to 3 of them, but they're trying to contact the others. Nothing the terrorists did kept the planes from talking to each other, so there is really nothing keeping the informed planes from radioing the information to the other pilots. (01:04:00 - 01:04:50)
Factual error: There is no airport in the world with a manhole cover in the middle of a runway. (01:14:00)
Continuity mistake: When McClane is fighting Col Stuart there is an up close shot where McClane kicks the Colonel and the Colonel grabs his leg. When the camera cuts away he is holding McClane's arm instead of his leg. (01:48:40)
Factual error: The payphone McClane uses in Dulles airport has the "Pacific Bell" logo. Pacific Bell is a West Coast phone company. (00:04:20)
Plot hole: The whole of Col. Stuart's plot to free General Esperanza and flee to a country with no US extradition laws would be rather impossible, as the plane with Esperanza and the terrorists would have been brought down by the US Air Force long before reaching international waters, especially given the fact that they would not maintain control over the airport landing systems after taking off.
Factual error: After recovering a pistol from a slain baddie, John McClane explains to airport security that it's a "Glock 7" (in actuality a Glock 17) and says that it's made of porcelain that makes it "undetectable by X-ray." Excusing the fact that not only Glock, but no major firearms company has ever mass-produced such a weapon due to functionality issues, it doesn't change that the ammunition would still be visible on X-ray. The armorer for the production team pointed these facts out on set and tried to convince them to change this detail, but they filmed it with these mistakes anyway.
Continuity mistake: When Mclane is desperately trying to get his fallen Beretta from the conveyor, he flicks the on switch to the conveyor. The terrorist then sprints down the conveyor to try and get the gun before Mclane, and you can see in the first shot of the terrorist running, that he is virtually at the gun immediately. The camera cuts to Mclane, and then back to the terrorist who is now significantly further away from the gun than he was before.
Factual error: Firing a full magazine of blank cartridges from an automatic weapon in the police station office as McClane does would be painfully loud. Nobody shows the slightest effect - nobody even winces. Some of the men wince slightly but their reaction is grossly underplayed. Obviously the sound was looped in later. (01:37:40)
Suggested correction: Every person jumps/winces and cowers out of the way of the bullets, one other officer even draws his gun in response.
What has never made any sense to me about this is that in a room full of cops everyone just stands around watching McClane seemingly gun down their Chief and only one officer even bothers to draw his gun.
Probably because everyone hates the chief. I wondered about that too.
Suggested correction: What makes the loud bang from guns is not the explosion of the gunpowder, but the bullet itself breaking the sound barrier as it leaves the gun. It's very noticeable when a gun fires a blank because it's so much quite, as the only sound is the small pop of the gunpowder inside. It's little more than the sound of a firecracker, but even more muffled by being inside metal.
I have shot blank and live with the military. Both are loud, but sound different. More of a crack with live.
Blanks are very loud: https://www.youtube.com/watch?v=z6PESH5LSE0.
Factual error: At the end when John lights the fuel with a lighter, this isn't possible with Jet A-1 which is what the Boeing 747 is fuelled with. This type of fuel is extremely hard to light. Even if you drop a match into a bowl of jet A-1, it will not ignite. Jet A-1 has to be compressed or have its temperature raised to a minimum of 38c/100f in order to ignite (which the compressing also does) so fuel in snow would never ignite in the way shown.
Factual error: When Holly's plane finally lands, the cockpit shot shows the pilot with his hands on four engine throttles. But Holly's plane is an L-1011 TriStar, which only has three engines. (01:52:00)
Factual error: Several runway numbers are mentioned in the movie: runway 10, 15, 25 right and 25 left. Runway 25 means course 250. The opposite end would then be Runway 7 (course 70). It would be unusual for an airport to have runways running course 70, 100 and 150, as that is way too close. And Dulles certainly does not. In the church occupied by the terrorists, the radar display (the upright one with the circular LED pattern, not a scope) shows the runway configuration of Las Vegas McCarran airport, not that of Washington Dulles airport. McCarran does have runways 25R and 25L, which are mentioned in the film.
Factual error: Near the beginning of the film when John McClane goes to the pay phone and calls his wife Holly on the airplane, that was impossible at the time. Those phones you see on the seats on the plane can only be used from the air to the ground not the other way around. Holly does answer on the plane phone and not on any cell phone she had in her purse. Not to mention even if it was possible to call the planes from the ground, they could do that to warn them of what's going on below and prevent more crashes. (00:04:20)
Continuity mistake: When Richard Thornburg is in the aeroplane bathroom giving his live report, in a number of the shots he is holding the phone upside down. (01:37:00)
Factual error: When McClane (Bruce Willis) is brought into Capt. Lorenzo's (Dennis Franz) office at Dulles Airport for the first time, Lorenzo mentions that McClane was in violation of several District of Columbia laws. Dulles Airport is in Virginia, not DC, therefore any DC laws would not apply to Dulles. (Although VA may very well have similar laws about airport misconduct.) (00:19:55)
Factual error: You cannot fire 'blanks' and 'live' ammunition from the same weapon without fitting a BFA (blank firing attachment). When a live round is fired, the bullet moving up the barrel seals the barrel. The exploding gas pushes in two directions. One - forcing the bullet out the end and two - pushing the working parts back. The working parts then move forward and pick up a new round. The BFA seals the top of the barrel, as a live round would do. If a live round is fired through a BFA you would be lucky not to blow the barrel.
Suggested correction: The terrorists in the film planned extensively for this operation, but the storm occurring may have just been a coincidence for them. They may also have had the plan waiting for a perfect opportunity, like a snowstorm. In the beginning of the movie, there's a news story on while the Colonel is exercising nude. The story says Esperanza's extradition has been long and drawn out, until a phone call from..." and he cuts the TV off. Given his connections, Colonel Stewart may well have been able to arrange a State Department call the week of a predicted snow storm. Esperanza's adherents may also have been able. Another scenario they may have had is to take the Air Traffic Controllers hostage (as they did) and have the other aircraft diverted for a supposed emergency, but the snowstorm worked out. Whatever the case, that element of the plot is an interesting discussion, not a mistake.
If the storm hadn't hit the pilots of the stranded airliners could easily have diverted to any one of half a dozen alternates, including a nearby Air Force base. They could do this without consulting or even contacting air traffic control. The whole plot falls apart from there - no hostages, no leverage, and who cares what happens to the people on the Esperanza's plane? They'd have it shot down.
That bothered me too when I first saw this in theatres. The chances of it snowing in D.C. on any particular day are pretty low, and the plan falls apart without it. The only way to 'fix' this is to assume that when the film was originally written, it was set in New York City. This makes more sense thematically...with the original set in Los Angeles. But at some point, probably late in the production, they changed it to D.C. for some reason, and made it fit as best they could.
The snowstorm was not part of the plan. Early on when the group of terrorists is sitting around the table about to exchange the package, Cochran is listening to a weather report and states that a huge storm is approaching, which makes the other men smile and one of them responds "God loves the infantry." The terrorists could still crash planes without the snow storm because they could impersonate the tower. The planes that are circling overhead are the planes that didn't have enough fuel to be diverted to another airport and that has nothing to do with a snow storm. The blizzard was simply fortuitous for the terrorists.
BaconIsMyBFF
The airliners we see could easily glide to any one of seven nearby airports from the airspace over Dulles, let alone fly there when fuel began running low.
That is a separate issue (and is indeed a mistake in the film) that doesn't really have anything to do with the blizzard. This film acts as if Baltimore Washington International or Richmond International Airport don't exist.
BaconIsMyBFF
And since they do, it is both a plot hole and a factual error. If they had called their fictional airport Springfield International, fine, but they didn't. They identified it as Dulles International which is within easy flying - or gliding - time to half a dozen other airports.
This is possible that other airports were closed due to bad weather.
Which necessitates the terrorists knowing that! They had to know the storm was coming for their plan to work. The stranded airlines could easily have diverted to an alternative even if that meant gliding, and they could do so without consulting air traffic control.
The terrorist obviously knew that. They are very arrogant and planned everything very accurately. They knew that other airports are closed because of the bad weather.
The airports were closed AFTER Esperanza's flight took off. The storm is an essential part of the terrorist's plans. Storms like the one we see can can diminish very rapidly or veer away from their original course (I have seen both happen) and cannot, ever, be counted on to the meticulous extent the terrorists do.