Corrected entry: In the street scenes of Washington, DC, the cabs are Yellow Cabs. DC does not have a yellow cab system, but rather "gypsy" cabs that come in all colors. There are actually very few yellow-colored taxi cabs. (00:21:30)
Corrected entry: In the final chase scene with McClane driving the semi along the freeway, none of the cars in traffic have drivers or passengers. You also notice that the cameras don't have any stationary shots so that it creates an illusion that the cars are actually moving. But if you use the street lights and intersections as reference you can see they're not moving.
Corrected entry: At the end of the movie the CIA helicopters are flying from DC to Baltimore. We see them over a wide stretch of water. Then there is a long sequence with McClane, and when we get back to the helicopters they are still over water. When you fly from DC to Baltimore you do not cross a long stretch of water.
Corrected entry: When McClane drives the SUV into the elevator shaft, you can see where the windshield has been "smashed out". There are wavy clean breaks along the perimeter of the lucite used as the glass. In reality, a windshield would shatter but still hold together in one sheet. It's impossible for it to break cleanly like shown in the scene.
Corrected entry: Henchmen are shown flying a helicopter over DC, with automatic weapons and such. After 9/11, DC has very strict airspace security, and a helicopter flying around without broadcasting its position would be beset by fighter jets in no time at all, especially if the helicopter was carrying armed men.
Corrected entry: When McClane and Farrell are stealing the BMW 5-series in Washington DC, Farrel hits the cars bumper with a trash can in order to deploy the airbags and prevent McClane from disabling the vehicle. Airbags do not deploy if vehicles are hit on the bumper with small objects, only if the vehicle is hit with sufficient force to trigger the airbag, usually by another vehicle or a large stationary object.
Corrected entry: Near the start of the chase involving the HAZ-MAT van and the semi, John runs into a black Mercedes Benz car, skewing it round to the left of the cab, later on in the chase, he hits exactly the same Mercedes.
Corrected entry: When the terrorist holding Lucy is shot in the foot, it is very clear that Lucy is wearing sandals, but when we see her feet from under the van as she kicks the gun to her dad, she has brown boots instead.
Corrected entry: The amount of data that is stored at Woodlawn is so massive, the computers need cooling towers. However, the DHS guy tells Bowman that Gabriel could load the data onto a portable hard drive. The problem with that scenario is that a hard drive of that size would be able to hold a minuscule amount of the data.
Corrected entry: When talking to Gabriel, McClane covers the camera with his hand and asks the Warlock to locate him, only to be told that covering the lens does not deactivate the microphone. So if Gabriel is aware that an attempt is being made to locate his position, why doesn't he take any measures? Especially when he sees McClane bursting out of the basement?
Corrected entry: Farrell's own cellphone was Nokia E61. In the car, Farrell used his car-lighter charger to charge the battery of the stolen Nokia 9300, which has different charger connector than his Nokia E61.
Corrected entry: When McClane drives the truck into the computer control room, he smashes into the Thai goon with high speed, and then slams her into a wall. Her legs would have been crushed by that impact, but she's not hurt at all, and we see her moving her legs around with ease when she's trying to climb up the truck.
Corrected entry: When the hackers have taken over the TV broadcast signal and the picture is being displayed in the FBI command centre, a message scrolls across the screen. Cut to another shot with John McClane watching the same TV channel as the FBI, the same message scrolls across, when it had in fact already been displayed.