A water treatment facility near Los Angeles doubled as the film's Woodlawn Social Security Administration building. The facility has miles of underground tunnels, and was also used in Die Hard 2 (1990) when Bruce Willis runs through tunnels under the airport.

The stunt featuring McClane driving a police car into a helicopter took three weeks to rehearse. The shot was accomplished by suspending the helicopter in the air with cables and combining two separate shots: one of the stuntman leaping from the helicopter and one of the car colliding with it. CGI was then used to delete the support cables and add rotor blades.

It took four months to assemble and combine archive footage of past American presidents from Franklin D. Roosevelt to George W. Bush to create the televised warning from Gabriel. The goal was to create a video representation of a ransom note.

The elevator shaft sequence was not in the film's script when Len Wiseman was hired as director. Wiseman added it because he associated elevator shafts and claustrophobic spaces with Die Hard (1988).

Bruce Willis' stunt double, Larry Rippenkroeger, was seriously injured when he fell 25 feet to the pavement. He suffered broken bones in his face and fractures in both wrists. Production was temporarily shut down. Willis picked up the tab at area hotels for Larry's parents and visited him numerous times at the hospital. Larry also doubles for James Caan in his television series, Las Vegas (2003). Caan came and visited Larry in the hospital and joked around for over an hour. Larry told his parents he was glad when Caan left because he hurt so bad from laughing at his jokes.

Continuity

In their first phone conversation, Gabriel tells McClane he knows him pretty well, as he's got all the info concerning him displayed, including all career records. Among the decorations received, we see he has been awarded a commendation in 1987 for the Nakatomi Tower incident in LA (referring to the events in "Die Hard"), and a citation for the swift resolution of the Chicago Airport Incident in 1990 (referring to those in "Die Hard 2"). This last record is wrong, as "Die Hard 2" was set in the Washington Dulles International Airport, and not in the Chicago Airport.

When the bad guy ("Rand") jumps from the helicopter (as McClain crashes the police care into) his headphones fall off as he hits the ground. But when the scene jumps back to him getting up from lying on the ground, Rand's headphones are magically (and mistakenly) back on.

Rand leaves Gabriel to go look for McClane and kill him. Later we see Rand finding McClane in the cooling room. But in between these two scenes we see Gabriel talking to McClane on the radio and slapping his daughter, and Rand is in the background, leaning against a wall. This editing mistake means Rand leaves to go look for McClane, comes back to Gabriel and waits, then goes to look for McClane again.

When McClane and Farrell are in the BMW the BMW Assist feature turns on. This function would be impossible since the service relies on a cellphone link and the cell systems were previously disabled by Gabriel.

When McClane is driving the semi, you can see him hit the same black Mercedes Benz twice.



Factual errors

Driving over fire hydrants in Washington DC would not cause water to spray out. The valves are located beneath the ground in areas where freezing temperatures are common.

Shooting a fire extinguisher will not cause it to explode like a bomb - at best, it will merely spew streams of its contents out thru any holes punctured in it.

The F-35 Lightning II shown in the film uses its VTOL engine to hover and shoot at its target. The VTOL (Vertical Take Off and Landing) engine is purely for that; taking off and landing. Hovering takes an incredible amount of fuel, and can overheat the hover engine since its duty cycle is not 100%. Additionally, the difficulty in making the craft successfully hover would make it virtually impossible to also track and fire on a target. As such, pilots are never, ever trained in or participate in hovering attacks.

F-35: When the aircraft is firing its cannon, two muzzle flashes are shown (one under each wing), when it is equipped with only one gun (a GAU-12 25mm Gatling).

The IP address that is displayed when the Metropolitan Transportation Authority is being connected to remotely is 192.24.647.90. The third number is not possible within the rules of IPv4 addressing, as it is larger than an octet (8 bits/0-255) can represent. This was not done intentionally by the filmmakers to avoid giving out a valid IP address, because elsewhere in the movie internal network addresses are used (10.x.x.x, 172.16.x.x and 192.168.x.x), and a real address is also shown, 202.218.154.52.



Incorrectly regarded as goofs

All the way through the scene with the F-35 attacking the 18-wheeler, none of the other cars in shot are moving unless they are run into by the truck. However, the cars aren't moving because they have been abandoned.

After McClane busts the BMW's window to break in, he's seen driving moments later with a window up and whole again. However, it is the back window which is broken, not the front.

If there are three power substations for the West, Mid-West, and East, and you have to physically be there to shut them down, then there should be two more crews out there that McClane didn't stop. However, Gabriel's henchmen explicitly say that they shut down the West and Central grids, and they were waiting on Mai's, prompting Gabriel to radio Mai, leading to his exchange with McClane.

When Thomas Gabriel pulls up McClane's police record, the record displays McClane's social security number as only containing 8 digits. (This may have been done intentionally by the filmmakers to avoid the possibility of giving out someone's real Social Security Number.)

In the scene where the antagonists trace Lucy's cell phone to call her, the display depicts her SIM card number as "270A486FC78". In reality, none of the serial numbers used to uniquely identify a SIM card to a cell network are alphanumeric; they contain numerical digits only. This may have been done intentionally by the filmmakers to avoid inadvertently giving actual SIM card codes.



Revealing mistakes

In the very first scene with Matthew, if you freeze frame the screen of his computer you can see the entire chat conversation he has with War10ck, which takes place about a minute later.

When Matthew is reading the name off of the registration card while talking to RoadAssist (0:59:27), the name Dvorak Tsajanski is handwritten, but the actual typed name on the card is David Seaver.

When all the street lights and turned green for the first time and John jumps on top of the vehicle to look at other intersections, you can clearly see farther away that traffic is moving fine and there are no accidents or traffic problems. Technically every intersection would be blocked and stopped and cars would not be moving freely.

After McClane shoots the driver of the truck, it sounds like the truck is shifting a gear up. Since the driver has been shot, there would be no one to shift gears. Furthermore, immediately after McClane gets in, it's shifting up again, although McClane is not yet driving the truck.

After McClane jumps out of the police car in the tunnel, the car's engine can be heard revving and accelerating before jumping into the helicopter, even though there is no one in the car pressing on the gas pedal.



Miscellaneous

Just after McLane turns up the radio playing the CCR song to wake up Farrell, the car is shown driving down the road with its 4-way flashers on.

At about 21 minutes in, as the helicopter is seen flying by, the sound is that of a 2-bladed main rotor helicopter like a Bell 206 JetRanger. But this helicopter is a Eurocopter AS350 Astar with a 3-bladed main rotor which makes a distinctively different sound.

When McClane and Farrell are at Warlock's (a computer hacker) home Warlock readily sends Gabriel's photograph to FBI Agent Bowman at McClane's request so that the FBI knows who's behind the cyber-attack. However, later on when McClane asks Warlock on the citizen's band radio to connect him with FBI Agent Bowman Warlock freaks out and initially refuses to do so.

At 1hr 50secs, McCaine and Farrell sneak up to a helicopter and try to open the door. It is locked, so they give up and move on. As the camera rises up above the helicopter to follow them, a wide open door is revealed on the pilot's side of the helicopter.



Anachronisms

After the West Virginia power station explodes and McClane and Farrell watch the electricity slowly shut down, there's a shot of an unspecified airport with the power going off. In that shot we see at least three Air Canada 747s taxiing or at their gates. Air Canada had already phased out and retired its entire 747 fleet at least two years prior to the year this movie was set (2007).



Audio/visual unsynchronized

When McClane and Farrell are shown driving to West Virginia in the stolen BMW, the interior of the car is quiet, as if all the windows are rolled up, but the passenger rear window is clearly shown to have been smashed to gain entry (and smashing of the window was a plot point), meaning the wind noise from driving on a freeway would have been substantial and would have made conversation difficult.

When McClane is in the 18-wheeler, he looks out the passenger window at the fighter pilot and calls him a jackass, but you can clearly see he said jerk-off.

In the scene after the natural gas blows up the Middleton plant when Matt's giving up on 'winning,' his words don't match his mouth. Also, the same shot is used 3 times during his dialogue.



Crew or equipment visible

Right before McClane reaches the door of the 18-wheeler, the shadow of a camera can be seen on the side of the truck.

In the overhead shots of the police car McClane is driving during the chase scene with the helicopter, you can see the cameras stationed on top of the side view mirrors of the car.



Errors in geography

There are no toll booths in Washington, D.C.

When McClane gets into the 18 wheeler after throwing the driver out, a freeway sign can be seen out the front window marked 118 West. This freeway is in California, not Maryland.

When the fighter jet is chasing the truck, McClane is driving on West Imperial Hwy below Highway 105 in El Segundo, CA just south of LAX (nowhere near DC). In fact, the stretch of road is made to look longer because the camera flips the scene horizontally several times (the truck at some points may appear to be driving on the left hand side of the road).

At the beginning of the film, McClane's commander locates him at Rutgers University (in New Brunswick, NJ) using GPS installed in McClane's car. However, the map displayed on the computer on his desk shows a map of Philadelphia. (Trenton, NJ is shown in the upper right corner edge of the map). Rutgers is another 30 miles to the northeast - well off the map.

There is no Middleton, WV. Also, when Matt and McClane watch the power go out from the power station, the view that is shown is not a view of any city in West Virginia. No cities in the state are that big or that flat. (The "Welcome" sign, however, is completely accurate as of 2007.)



Plot holes

McLane and Farrel use RoadAssist (an OnStar type system) to start the car they steal remotely, but it has already been very well established that all forms of satellite peer to peer communication (including cell phones) are down at this point, so this would not work.

Even if the terrorists had stolen a real government hazmat van (as opposed to simply painting a civilian van), it couldn't have been located since all the cell systems were down at that time.

There is zero reason for the FBI to ask New York City to send an officer out of state to apprehend a suspect in Camden, New Jersey. New Jersey State Police or the Camden police would be asked apprehend the suspect. If the FBI wanted to do it themselves, they could send an agent from the Philadelphia field office as it is across the river from Camden.

A big deal is made about the terrorists having to physically go to the power station to interrupt the grid. But even after losing security access to its computers, they are still able to blow up the facility remotely.

While driving McClane and Farrell to the Federal building, the FBI agent calls dispatch on the radio to get DHS to clear a lane for them. Despite Farrel and McClane not speaking at all at the time, somehow Gabriel's scanning equipment makes an exact voice match with Farrell and somehow they instantly know who McClane is, despite not having any connection to him prior to that. There is absolutely no way they could have known who was in the car simply from the agent making a short radio transmission.



Character error

When Gabriel calls to the F-35 overhead, he identifies it as "AV Eighty-One". Real air traffic control or military command would have called it "Alpha Victor Eight One", using the proper phonetics for radio communication.

When Thomas Gabriel pulls up McClane's police record, it makes no mention of his time as an LA Cop (in Die Hard 2 (1990) he explains he has switched to the LAPD to be with his wife).

During his CB conversation with Agent Bowman while driving the 18-wheeler, McClane says, "If anything happens to me, send in the Calvary." Calvary is a name of a hill near Jerusalem used as a site of public crucifixion. What Bruce Willis obviously meant to say was "cavalry," which refers to a unit of mounted troops - formerly on horseback but more recently in helicopters and by other means. This error appears on the theatrical version, but not in the unrated version.

Despite being incredibly hungry, apparently, Farrell ignores the Snickers bar in the glove box of the BMW they steal.

In the scene when Thomas Gabriel asks John McClane about his ex-wife Holly and their divorce, the divorce certificate reads Holly's birth year as 1967 and John's 1955. The marriage year below reads 1979 in which is practically illegal since Holly would only have been 12 years old and not at the legal age of marriage even in 1979.