Factual error: The payphone McClane uses in Dulles airport has the "Pacific Bell" logo. Pacific Bell is a West Coast phone company.
Factual error: Prior to the 747 take off, a Major Grant is sucked by one of the engines and all we see is blood being spit from its exhaust. Turbofans are very sensitive and would collapse after sucking a heavy bird (like a vulture), but this one remains intact after sucking a 200 lb man.
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.
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.
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.
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 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.)
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.
Factual error: Firing a full magazine of blank cartridges from an automatic weapon in the police station office as McClane does would deafen everyone in the room. Nobody shows the slightest effect.
Factual error: Since the terrorists have implausibly taken over all the radios at the airport, the good guys use the marker beacons to communicate with the airplanes. Even if they could be modified to talk rather than beep, marker beacons (outer, middle and inner) are on the approach path of a runway, and only transmit to an aircraft as it passes overhead. The signal is only picked up by an aircraft's marker beacon receiver, if so equipped. There is not enough time to get a message. Nor could a marker beacon be used to broadcast to a large number of airplanes. The outer marker is only 5 miles from the airport. At most, one airplane would be holding over the outer marker.
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.
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. At least a good 20 seconds passes before he ejects from the plane and the grenades go off. Normal grenades would have gone off long before 20 seconds.
Factual error: When the bad guys 747 is blown up it is about 40 or 50 metres off the ground and travelling at take-off velocity, yet when Holly's plane is landing you can see that the debris field is perfectly circular. Surely the 747s speed and angle of descent would mean the debris field would be elongated?
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.
Factual error: When the 747 explodes, fire is rushing up through the cargo hold. Esperanza - in the cockpit - looks back over his shoulder as if seeing the fire coming. Clearly he can't see the fire - since the view we are seeing is inside the cargo hold and cabin. But why is he then turning his head and looking back against the cockpit wall? And the flash we see on his face - from the explosion - that would not be there until the fire was inside the cockpit. And that would go so fast that he wouldn't have time to scream.
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.
Factual error: Shortly after the terrorists first start taking over the airport, the airport's chief engineer is shown scurrying about with an E6B flight computer in his hands. The E6B is a mechanical device, usually made out of aluminium, that is similar to a old-style slide rule. But it is used only by pilots to calculate things like course corrections due to winds - there is absolutely no reason that an airport chief engineer would carry one on the ground, especially in a time of crisis. Plus the mechanical E6B, even by 1990, had largely been replaced by electronic calculator type E6Bs by the airlines and even many private pilots.
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.
Factual error: At the end of the movie, all of the planes come in to land by the fire. However, the planes are far, FAR closer than any large aircraft would land to each other. FAA regulations would have the aircraft about 5 miles away from each other. If they're landing this close due to "emergency", there would be wicked wake turbulence at such close distances.
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.
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). No airport would have runways running course 70, 100 and 150 - that is way too close. And Dulles certainly does not.
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.
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.
Factual error: Bruce is sitting in what looks like a C-130 while terrorists throw grenades in it through the window. Never mind the grenades going off too late, because they wouldn't all have made it through the small window anyway. In fact some of those grenades would've bounced back killing the terrorists also, which would've made for a surprising end to this movie.
Factual error: In the scene where Bruce Willis faxes the finger prints of Oswald Cochrane to Sgt. Al Powell in LA, I don't see how you can determine the prints through a fax. They would appear as blobs on the other end.