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)
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: At the time Die Hard 2 was made the only people in the Army that wore black berets were Rangers. If anything an SF (Green beret) team would be responsible for providing aid in that situation. (01:03:15 - 01:28:15)
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)
Continuity mistake: When Col. Stuart is talking to Gen. Esperanza on the walkie-talkie about what runway to land on, behind Stuart you can see one of his men walk up to the map of the runways. Stuart turns around and starts walking to the map and the guy isn't there anymore. When Stuart gets in front of the map, the guy comes up and tells him which runway Esperanza should land on. (01:09:05)
Factual error: The terrorists are using Kenwood 46AT Handheld Radios that operate on 440Mhz. The Army moves in with a Kenwood TS-850 Radio that operates on 30Mhz-3Mhz. Nowhere near the frequency that the terrorists are using. (01:11:30 - 01:25:40)
Continuity mistake: Bruce Willis is emerging from an underground air-vent when the plane with General Esperanza is landing. Initially the plane is coming on a direct course for him and he struggles to get out. In fact the front wheel is on course with and knocks the vent cover. But in the very next scene, the tire marks clearly show the front wheel passed to the right of the vent and so completely missed it. (01:11:40)
Continuity mistake: When John is coming out of the drain on the runway, in shots facing him it's snowing, and in the shots that face both John and the plane, it's snowing. Yet, when the camera is just on the plane it's not snowing. (01:13:30)
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 desperately trying to get out of the manhole cover to avoid the plane, he props it open with a steel bar. Moments later, just before the plane runs over it, the bar is gone, so there should be nothing holding it open. The size of the gap between cover and runway also decreases between these shots. (01:14:50)
Factual error: The plane from which Bruce Willis escapes by using an ejector seat is a non-existing plane. The fuselage is from an old transport plane from the US Air Force made by Chase. But there has never been a Chase with 4 engines buried in the wing. America uses underslung engines. In this case, it is the wing of an Arado Blitz prototype from the second world war and the fuselage of a Chase cargo plane. (01:15:10)
Visible crew/equipment: When we first see McClane on the snowmobile, marks from the camera snowmobile are visible. (01:27:20)
Revealing mistake: Throughout the whole movie, bits of 'snow' stuck to various things in close up view (i.e. guns, hair, faces, clothing). Look closely at the snow, its quite obvious that they are actually little thin scraps of white plastic. Most evident is in McClane's hair when the platoon is about to move in on the church, the shot of him saying "You're not such an asshole, after all." (01:27:55)
Factual error: The chase scene involving the snowmobiles is problematic in that McClane can actually see where he's going. In driving snow, it's often difficult to see, as snow blows in one's eyes. On a speeding snowmobile, in heavy snow and with no eye protection, it would be practically impossible to see anything. (01:31:15)
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: 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.
Continuity mistake: During the last fight scene on the wing of the plane, just after the guy is sucked into the engine, general Stuart comes rushing out and yells something like "it's time for the main event". At this, John rolls over onto his back. The shot then switches to much further away, and he is still on his stomach. The camera cuts in close again, and John is back on his back, and sliding towards the center of the wing. The camera cuts away again and shows John back on his stomach and just now rolling over. (01:43:40)
Factual error: After the fight with Colonel Stuart on the wing of the plane, Bruce Willis falls down from the wing. As he falls, watch the tyre-tracks near him. Those are definitely NOT the tyre-tracks of a plane. A jeep or a truck, maybe, but not a plane. (01:44:45)
Continuity mistake: McClane's fireman's jacket gets progressively bloodier throughout the film, but around the time when he is fighting the terrorists on the planes wing, it is miraculously clean again. McClane is not wearing it, but it does get cleaner. (01:45:50)
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.
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.