During the scene with McClane in the tower talking to the Air Traffic Controller and the Police Chief, there is an obvious overdub in TV versions with a completely separate voice and obvious audio/visual mismatch.
Throughout the entire movie, Lorenzo and everyone else refer to him as Captain. He also wears Captains bars on his lapels. Near the end, when he is assembling the rest of his men, he says on the P.A. "this is Chief Lorenzo". Chief and Captain are two different ranks for police officers.
During the fight in the luggage room with the black terrorist, John McClane strikes him with a golf club. When he wants to strike him a second time he swings the club over his left shoulder. But just before he strikes, the camera viewpoint changes and you see him (or actually his stunt double) swinging the golf club over his right shoulder. This is probably because Bruce Willis plays John McClane as a lefty. But the stunt double seen in the second shot must not have known that.
When McClane sends the fax with the fingerprints, the page is sent upside down. When Powell receives the fax the page is turned right side up. Faxes are received in the same orientation as they are sent.
When John is using the torches to try and show the ground to the plane coming in too low, he is shown waving brightly lit torches but when the camera shows only him, there is no light reflected from the fire.
As General Esperanza's plane is landing. McClane gets up to the runway via a ladder. As he is approaching the ladder we see the base of the ladder is up a step. However an overhead shot of McClane reaching the ladder shows it to be in a large pool of water.
When McClane is in the tunnel under the runway, the manhole cover is lit from above. It is night outside, and the light from the landing lights wouldn't shine directly down the manhole. Furthermore, in shots of the manhole from the runway, it is lit from beneath, not above.
When John falls off the 747's wing and tumbles towards the camera, there are no trails in the snow after the 747. The 18 wheels should make 10 trails when the aircraft goes along a straight line. The only trails seen are the trails from the car filming the scene.
After falling from the exploding snowmobile, McClane examines the automatic weapon he was using to see why his shots did not hit anything. He pulls and examines one magazine with a blue band from the gun, but after the closeup shot of his realization he can now be seen holding two magazines, one with a blue band and one with a red band.
When Col. Stuart is talking to Gen. Esperanza on his hand held radio, he turns around to the glass radar display in the center of the church. A dark haired terrorist holding some rolled up maps is already stood at the display. In the next shot, when Stuart walks up to the radar display, the same man with the maps walks up to the display again.
Early on in the film when the bad guys are discussing the incoming weather front, the evil henchman holds his hand to his left ear to better hear his radio, however in the next shot his radio is in his right ear.
The pilot of the plane which was deliberately crashed by the terrorists informs the "tower" (really the bad guys) that the airliner is "running on petrol fumes", presumably about to run dry. Yet when it strikes the runway it explodes like a small nuclear weapon.
As the airport police begin to leave for the hangar housing Col. Stuart and his men, they pull away from the terminal straight ahead and cars can be seen at the exit through Lorenzo's windshield facing the same direction. The taxi they hit pulls directly across their path, but as seen in a following shot of McClane running over to Samantha Copeland and her crew, there was nowhere for the taxi to go except straight into the terminal building itself.
(at around 1h 45 mins) As McClane rolls along the tarmac after being kicked off the wing of the plane, there are tire tracks in the snow from the camera vehicle (and not, as would be expected, from the aircraft).
A military flight carrying a high profile foreign prisoner would not be scheduled to land at a civilian airport but at a military airfield. Under the scenario in the movie, if General Esperanza was to be routed to Washington DC for the DOJ he likely would have landed either at Bolling Air Force Base, Andrews Air Force Base, or even Fort Belvoir (US Army).
Reagan National Airport and Dulles International (IAD) are only 27 miles apart. However, Baltimore/Washington International (BWI) is still only 57 miles from Dulles by road, 46 from one to the other directly. In the movie, we are informed that National has closed due to weather conditions, but BWI is never mentioned, even though it was dedicated in 1950 and acquired by the State of Maryland in 1972. If the planes low on fuel could circle for 90 minutes, they could have easily been redirected to BWI.
If you look closely at the flight boards when the flight times are being changed to "Delayed", in the second scene of the flight board close-up, Auckland is misspelled as Aukland. Also, at the time of filming, no commercial jetliner could fly Auckland-Dulles nonstop (7,476 nautical miles). Airliners capable of serving this distance did not enter service until 2002, or 12 years after the movie was released.
After McLane's airport shootout with the mercenaries, Lorenzo accuses him of violating five District of Columbia regulations. Dulles Airport is actually in Loudon County, Va., about 25 miles West of Washington D.C.
While somewhere over Ohio we are told the pilot has just been given information by Dulles Tower. An en-route commercial jetliner at cruising altitude over Ohio would be communicating with Cleveland Center, not Dulles or any other airport control tower.
There is a general "V" shape to the Dulles Airport property. However, the area between the two legs of the "V" do not have public access. There is no church located in this area that would have cabling for the airport running underneath it.
The bad guys wear DWP (Los Angeles Department of Water & Power) vests to the church, not vests with "Dominion Virginia Power". Dominion Virginia Power supplies electricity in Fairfax and Loudoun Counties in Virginia where Dulles Airport is located. DWP operates in Los Angeles, California.
After taking out the two terrorists in the baggage area, McClane identifies their weapon as a "Glock 7, a porcelain gun made in Germany," and says that the pistol can pass through a metal detector and not set it off. This pistol is an Austrian-made Glock model 17. Glock pistols do have a polymer frame, but the barrel and slide are still made of steel, which is more than enough metal to set off a metal detector. Glock pistols were the first with a polymer frame to be widely marketed, and this was a common misconception at the time.
The baseball style hand grenades used to blow up the military transport with McClane on board have a fuse burn of about 5-7 seconds before detonation. From the moment the first one is thrown (releasing the spoon and igniting the fuse) to the explosion, 37 seconds elapse. While it's possible that the mercenaries may have put extended fuses in the grenades, why would they, as McClane's escape illustrates exactly why a short burning fuse is desirable?
When Trudeau finds out the airport has been taken over, he orders all aircraft to their alternate airport other than those that have already started their approach. All of these, he orders to "hold at the outer marker." The outer marker is a beacon 5 to 7 miles off the end of the runway. If "all" lanes held at that spot, it would be very dangerous.
The NEA aircraft Holly is in is a TriStar L-1011/DC-10 type of aircraft. Towards the end of the movie there is a shot with Holly and the stewardess. In the background there is a shot of stairs going up stairs towards the flight deck. These type of airplanes do not have stairs. Only in the 747 in the 1990s.
A 747 does not have a fuel dump valve in the pylon (engine mount). Any fuel dump is controlled from the cockpit and fuel is ejected from nozzles on the trailing edge of the wing, one on each wing just inboard of the aileron.
The seat layout on the NEA flight is incorrect for a Lockheed L-1011 Tristar. The seats appear to be arranged in a 3-4-3 layout like that of a Boeing 747, instead of the standard 2-5-2 layout for the L-1011.
When the terrorists are taking off in their 747, after the General detects that the aileron has been tampered with, he is applying forward/backward pressure on the controls but the controls look stuck. Forward/backward motion controls the elevators and other pitch controls. The ailerons help turn the plane, so the controls would have been jammed side-to-side, if at all.
McClane impeding the aileron on the terrorists 747 wouldn't have prevented take off, since they are used to turn the plane. The plane could have taken off and the General could have flown the plane, although difficultly, compensating for the aileron with the rudder.
While normal practice would have been to use an internal plug to get automatic rifles firing blanks to cycle, which would make the weapon explode when shifting to live ammo, Stuart's team could have devised another mechanism. Nevertheless, any mechanism would have to be removed and the movie answer is merely to switch magazines which couldn't possibly work.
The handheld radios used by the terrorists are on the 440MHz amateur band, yet the base radio used by the army in the tower to attempt to decode the terrorist's transmissions is clearly showing a 144MHz frequency on the screen.
The Fairchild C-123 Provider is not equipped with ejection seats, a highly unusual (and inherently dangerous) crew escape system for a cargo plane slow enough to simply allow bailing out of the nearest door.
While on the airliner, reporter Thornburg asks his sound man if he can pick up air traffic with his wireless microphone receiver. The man responds, "they should be on our band", and proceeds to tune in air traffic. This is impossible. Wireless microphones are channelized, and the receivers cannot be tuned around, much less would he know where to tune. Wireless microphones are not on the same frequencies as aircraft, and are wideband frequency modulated. All air traffic is amplitude modulated.
When McClane, the Army commander and the Police Chief are arguing outside in the blizzard, the amount of snowfall on the Police Chief's jacket keeps changing. The first time the camera shows him, there's a lot of snow on him. The camera flips away, and then back, and his jacket is cleared of snow. The camera flips away and back again, and this time there's snow on his jacket again. However snow can melt and fall off a moving persons clothing, or simply be brushed off periodically. Snowfall can also give sudden flurries.
When Trudeau addresses the aircraft before their communications are cut, the Fuji Air plane shown is a Lockheed L-1011 Tristar. The next time it's seen, during the end credits, it's a Boeing 747. Furthermore, it would make more sense for the Fuji Air plane to be a 747, because in real life, a Tristar could never fly nonstop to Dulles Airport from anywhere in Japan. It is however entirely possible there is more than one Fuji Air flight.
The entire premise of the movie, is that shutting down the communications of an airport, will leave the overhead aircraft helpless and uninformed. In fact, any Flight Service station transmitter, airport, aircraft radio shop, or aircraft, within fifty miles, could have alerted those pilots of the situation. Literally, there would be hundreds of radios in the area, that could be used to end the terrorist plot.
Several shots show the view from the Control Tower where the visibility is good enough to see the runways and even the lights from the airport perimeter. This would mean that there would have been enough visibility to land airplanes. Also the crash at the beginning would not have happened because their glide path put them on the runway, the pilots would have seen the ground in time to avoid it.
When Esperanza's aircraft is coming in and they are lighting up a runway, Col. Stuart tells the tower, "do not attempt to land any planes, we are monitoring you." Before that, Barnes had turned the outer marker into a way to talk to the planes without Col. Stuart knowing, therefore, the tower would be able to tell a few of the planes near that particular runway to sneak in before and after Espinozas plane. And, since the planes have been told not to listen to the towers regular frequency, Stuart would not be able to retaliate by downing another plane.
About 20 minutes in the film, when McClane takes fingerprints from a dead terrorist on a gurney, the stiffs hand keeps lifted. That is impossible because the man is only just deceased; for a hand, rigor mortis has to set in. That will happen between 2 and 6 hours after somebody has passed away.
When the planes land on the fire trail we see a line of them coming in. If they were that close together, especially under the blizzard-like conditions depicted, they would all crash into each other on the runway; there simply isn't enough time between landings for all of them to taxi out of the landing path. However this optical illusion is caused buy telephoto lenses - it's called compressed perspective.
When McClane and the reporter are kicked out of the control tower, they are sent down the elevator. McClane climbs out the elevator escape hatch before the elevator stops and it is met by two airport police officers. But as the elevator doors open, the two officers are already looking UP into the elevator, as if they knew McClane was gone, even before the doors opened.
In the luggage room, when McClane sprays the can at the black terrorist, the other terrorist shoots the can, blowing it up. It then shows another take of McClane dropping the can, but it is now fully intact!
When Thornburg shuts himself in the bathroom in order to phone the studio, the overhead shot clearly shows that the toilet is fake; lined with silver foil, rather than an actual metal fitment you'd expect to find in a plane.
When Col. Stuart asks his henchman to give him a flight number that is low on fuel, the henchman hands him a transparent slip with the information for Windsor 114, which lists the model of the aircraft as a 747, but the plane itself as seen in the movie is in fact a Douglas DC-8-60, not a Boeing 747.
Prior to the Windsor flight crash, the airport runway seems to be completely covered with snow due to the storm, however, the view outside cockpit window immediately before the plane "crashes into the concrete" clearly shows the runway markings.
The hand held device used by Col Stuart to communicate with the control tower is actually a 20hz, sound-powered telephone (nomen, AN/TA-1/PT) used for many years by the US military to troubleshoot tactical telephone lines. The maximum transmission range is no more the 1 mile using only physical wires.
The goof items below may give away important plot points.
When the man in the church is shot, there's a close shot of the villain aiming and pulling the trigger. In the next shot the dead body is thrown backwards over some benches. In the background the villain is holding the gun straight downwards. The following close shot shows the villain aiming again.
At the end of the film we can see Holly's plane, just before the old lady shouts at Thornburg. The "NEA" letters can clearly be seen washed out at the upper half and another caption becomes visible. The next time we see it from a different angle, when Marvin arrives, and the upper half is just fresh white painted.
Just after John gets thrown off the left wing of the terrorists' 747 - and we know he opened the fuel dump valve before hitting the ground - the aircraft swings onto the runway for take-off and opens throttles. Then when John utters his famed expletive and lights the fuel trail ablaze, the line of fire that follows the plane down the runway is seen to follow the #3 (RIGHT inboard) engine. But in the next shot, as the plane climbs higher, it's the #2 (LEFT inboard) engine that blows up, triggering an explosion of the entire plane.
The engine Grant is sucked into is clearly a different one than those on the plane. The center cap on the engines on the plane have a silver center with a black surround with a "spiral" painted on it that shows the engine is spinning. The center cap on the engine Grant was sucked into was all silver, with no "spiral" on it.
Stuart takes a rifle with him when he goes to fight McLane on the airplane wing. It disappears just before he goes outside. (Enough time passes between shots for him to have put it down, but under the circumstances, why would he?)
Cool-looking explosions seen when planes crash are caused by fuel, of which flight Windsor 114 had precious little. With hardly any fuel, a more realistic crash would've seen a much smaller fire, probably with much less lethal consequences. Furthermore, as the fuel tanks are located in the wings, a progressive back to front series of large explosions over the full length of the fuselage makes no sense.
When Grant is pushed into the engine at the end it would have caused serious damage to the engine. 747 engines can ingest a large bird and still work but a whole person including clothing etc. would cripple it.
At the end of the film, Richard Thornburg has been taken off the plane by person or persons unknown, still badly dazed and immobile from having been tasered, and left to lay on the snow-covered tarmac. No one else on any flight is injured, yet all receive prompt medical assistance from dozens of responding airport paramedics. No professional paramedic, having known what Thornburg had been up to on his flight or not, would leave an injured man in the snow and attend to other people who do not require assistance.
The bad guys adjust the ILS system to set ground level for 200' below actual ground level in order to cause the Windsor flight to crash. This is not possible because the ILS system uses antennas mounted on the ground around the runway which send out signals to the receiving plane. The system is based on how far and where the plane is relative to the antennas. The antennas would have to be physically moved in order to change where the ILS glide-slope would be. Even if they were put 200' below ground, the signals would not reach an airplane.
When John blows up Colonel Stuart's plane, the pilots see the flame and use it as a guide to land. The fire from the earlier crash couldn't be used the same way because there was no fire trail marking out the direction of runway.
At the end when they show the shot of all the aircraft, they are all parked very close together and in skewed positions. If they had all followed the same landing path as indicted they would never have been able to park in such positions.
The Evergreen 747 the terrorists escape on is strictly a cargo 747. There are only enough seats for about 4 passengers in the top part of the aircraft. Also the door over the wing is welded shut, there is only one operational 'passenger' door and that is at the front of the aircraft. All other doors are welded shut and all windows are painted over.
Look carefully at the 747 that the terrorists use to try and escape from Dulles Airport while it is still inside the hanger, and you will notice that in several shots, its tail is completely missing. Also the rear tail wings are not visible as they should be with a head-on shot. The tail wings are higher on the fuselage than the main wings on a 747.