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: 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: 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)
Suggested correction: If the pilots are given an incorrect altimeter setting (outside barometric pressure), then yes, they can be fooled as to their altitude.
Even if the pilots would've been given an incorrect QFE for the barometric altimeter, the radio altimeter would've still given the correct altitude, and there's nothing the bad guys could do to mess with it.
Factual error: When the terrorist clears the nearly fuel-exhausted plane to land on the lowered ILS, the terrorist says, "Windsor 114, you are cleared to land on Dulles Runway 29, ILS." Problem is: There is no Runway 29 at Dulles. The closest runway alignment for a 290 degree heading is Runway 30. (00:53:35)
Suggested correction: Runway numbers are based on the magnetic heading of the runway, and since the earth's magnetic field is in constant motion, a runway's magnetic heading can and does change over time. As an example, my local airport's main runway is 30/12, but 10 years ago it was numbered 31/13. Therefore, it is possible that in 1990, what is now runway 30 at Dulles was numbered 29.
Random guesswork isn't a valid correction. A simple google search will show that runway 30 at Dulles has been called that since it was opened in 1962. In 1990 there were 3 runways at Dulles: 1C/19C, 1R/19L, and 12/30.
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)
Suggested correction: The fuel would not light at all, so the tightness of its trail is really unable to be determined in this manner. Assuming jet fuel could light like that, it's possible that only the densest area would be able to catch, which would be the center of the trail... but again, Jet A is pretty hard to catch on fire.
Continuity mistake: When the army truck arrives at the 747 hangar, we see a line of snow on the ground behind it. The actual truck has no snow on it at all, despite its journey to the hangar.
Suggested correction: Snow doesn't generally accumulate on a moving vehicle. Anything resting on the vehicle will blow off once it's in motion unless it's very wet and/or heavy.
As a truck driver, I can tell you that the conditions shown would have snow accumulating on a moving vehicle at least in some places.
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.