Factual error: When the police officer first comes to the tower and looks around there is a football game the terrorist is watching on television. The movie takes place on Christmas Eve. The Southern California vs. Notre Dame game, which is the one being played in the movie, is a classic rivalry game played in either late November or early October. This is especially true in 1988 as ND and USC were ranked 1 and 2. Notice the terrorist display displeasure when the announcer notes that ND just scored. USC is the home town team. It is also apparent that the game is being played during daylight hours, but at this point it is dark outside.
Continuity mistake: When John and Karl are fighting and Karl reaches for the gun lying on the floor, John legs it out of an open door. Karl fires two shots, the first hits John and the second sprays blood all over the door. (01:47:35)
Continuity mistake: After McClane "kills" Karl by hanging him with the chain, Karl can be spotted at the top of the stairs on the right side as McClane is reloading his gun. (01:53:30)
Character mistake: In the infamous 'shoot the glass' scene, Alan Rickman, playing a German, commands to 'Schieß den Fenster', which is wrong in German because the 'Fenster', the window, has in fact the neutral article 'das' instead of the masculine 'den'. Also, it is not a window in German but a 'Fensterscheibe', a window pane. In German he would say 'Schieß auf das Fenster' ('Shoot at the window!') or 'Schieß auf die Scheiben' ('Shoot the window panes!'). (01:36:00 - 01:37:30)
Factual error: If the hose hanger isn't heavy enough to instantly yank McClane out of the window, but instead slowly pulls him down, then it should be light enough for McClane to simply stand up and reel it in. If his weight is enough to slow the hanger's decent, then that means it only weighs slightly more than he does. He should have no trouble standing up and walking backwards to pull the hanger back up. The mistake is that the hanger pulls him slowly at all, it should have yanked him directly out of the window the second the line ran out of slack because McClane is not anchored to the floor in any way. This scene suggest that the hanger is both heavy enough to pull McClane but light enough that McClane's weight significantly slows it, which is impossible.
Continuity mistake: During the fight between Karl and McClane, Karl shoots at John and it hits him in the shoulder. That wound then disappears and reappears several times throughout the movie.
Continuity mistake: After John McClain has jumped off the top of the building, and the firehose hanger has got stuck to the railing, he has stopped at the top of the window, but in the next shot he is near the middle. (01:51:55)
Revealing mistake: Having leapt from the rooftop, Bruce has his feet planted on the window. As he then goes to push himself back in order to smash the glass with his gun shots watch the rope. Someone above has kindly held the rope out several meters away from the building in the next shot, allowing him to get a much bigger swing.
Factual error: Cutting through phone lines will not electrocute you. At best there a 80v AC ringing current per line which gives a mild shock. Also, when the technical expert kits the data cabinets the sensitive electrical equipment is highly unlikely to explode in a shower of sparks.
Factual error: The news reporter is listening to the police scanner, when Willis is heard talking, the channel lights that blink on the scanner are supposed to stop on the channel being used, but they keep flashing. (00:55:50)
Revealing mistake: Bruce Willis jumps off the roof with the firehose. The hose hanger breaks off the wall and apparently gets stuck in the railings. The shot is very careless: slow motion shows that the firehose doesn't get stuck, but simply clings like a magnet to the top of the railings. (01:51:50)
Continuity mistake: When John and Al are talking, if they have any kids, there is a shot of John's family in his wallet and you can see both thumbs on the wallet. The scene cuts away to John talking, and his left hand is holding the walkie-talkie. There isn't enough time for John to grab the walkie and start talking into it.
Visible crew/equipment: When John gets out of the limo at Nakatomi Plaza, a stage light is reflected clear as day in his door. (00:08:10)
Continuity mistake: When the FBI shows up and Duane Robinson is explaining to them what the police know, Al tells the FBI about John. Duane is in front of Al in the shot looking at the building, and right next to him in the opposite angle.
Visible crew/equipment: The shadow of the camera is visible right of screen when John is wrapping himself with the fire hose and asking himself why he's doing it. It lingers for some time. It looks to be a steadycam with a monitor.
Continuity mistake: Hans leaves his gun and flashlight lying on the ledge out of sight. When he edges back to get it, the gun is upright, easy to grab.
Revealing mistake: When McClane is on the roof shooting over the hostages the helicopter appears and they start shooting at McClane, the squibs used for the helicopter shooting scene are visible lying on the roof and explode in sequence, starting at the back and moving toward the camera as McClane does.
Continuity mistake: When McClane goes onto the roof at the end he shoots Uli as he opens the door and the blood splatters all over the wall at the side, but when McClane walks past the body there is no blood on the walls or steps or where the body is lying.
Continuity mistake: When the terrorists arrive the truck reverses up to the loading bay and a tail lift is deployed, but at the end when the ambulance is unloaded the tail lift has been replaced by ramps. Tail lifts are bolted to the truck frame and simply cannot be removed.
Visible crew/equipment: McClane runs up the stairs and looks on floor 31. He goes up another floor as the camera follows. The camera operator's shadow is blatantly visible left screen.
Answer: We don't know what John would have done in that circumstance. Obviously Hans was planning to kill everyone with the explosives anyway at the end. Perhaps John would have suspected that. Also, doing that would invite more police incursions.
Greg Dwyer
Hans thought Ellis was a good friend of John's and John still didn't give up when he was going to shoot him. If John wouldn't save his friend, why would he care about others. Plus Hans told Karl earlier he could stall the police but not if they heard gun shots. The police would have absolutely stormed the building if he started killing the hostages.
Zorz
The fact that we don't know how John McClane would have acted doesn't remove the fact that it would most likely have been a good way to coax him out. Also, depending on when Hans Gruber would have decided do implement this strategy, John probably wouldn't have known about the explosives on the roof as he only finds out about them at the 3rd act break. As for the "more police incursions" part, I couldn't disagree more; Hans already killed two hostages - one on speaker with the police -, all the cops in LA seem to be there already, and don't forget that the involvement of the FBI is part of their plan anyway. This is definitely the one major plot hole of this otherwise perfect film.
It would have been, but plenty of movie plots don't pan out the "perfect" way without it being a plot hole. Killing Ellis is a reasonable first step, it doesn't work, and then the events of the plot pick up pace - Gruber goes to check the detonators, as that's a priority. He's hoping/assuming they can get through the rest of their plan by isolating McClane, or at least prevent him causing more chaos. They want the power shut off - they don't want to cause such massive carnage that the building is stormed before then. They need to get helicopters, blow the roof, and escape as planned. Hans doesn't want to derail things any more than they already have been.
Jon Sandys ★
Seems to me like they have all their bases covered; the police isn't even able to get in with a tank as he blows them up so I don't think the police "storming the building" is even a possibility in the reality of the film. Also, after blowing up that tank, that's two hostages and a bunch of cops dead so I would say the situation is pretty derailed. Everything is going as planned for Hans and his team, except for McClane, so he should be in damage control mode and this is an obvious solution. He doesn't even have to change his plans, just tell McClane he's gonna kill one hostage every 10 minutes until he shows up unarmed and tell one of his henchmen guarding the hostages to do it while they go along with the plan and maybe even try to find McClane at the same time. I think this is something Hans should have at least considered, but the screenwriters just didn't think about it/didn't want to address because they couldn't think of a good reason for him not to do it.
There are no cops dead, Hans says "Just wound them" and despite the awesome explosion, the APC isn't actually penetrated or destroyed. But Hans needed this to turn into a standoff, a show of force would prevent a SWAT raid from expediting the deadline, he needed to get all of the hostages up on the roof to make his getaway downstairs, and executing a bunch of them would bring suspicion onto how cooperative he is (His plan to blow up the roof relies heavily on the police sending in choppers) they cooperate with him, which they won't do if they think Hans is a crazed lunatic who's only interested in more and more carnage, if he wounds the cops and only shows he can defend himself, and that he was being reasonable. The cops would play ball, and they would believe he's willing to spare the hostages lives, plus he always planned on taking one hostage as a contingency, if they thought they were gonna be killed they'd become a liability. Patton Oswalt talks of a real plothole though lol.
John McClane would know they'd kill him as soon as he shows up, as soon as he heard "We'll have to tell Karl that his brother is dead" he knew that all bets were off, he lost his chance to end it civil, if they had no personal connection to the first terrorist John kills then maybe putting 5 people into a room and doing an Air Force One on them would work, but not when John knows he'll be body number 6. Al says it best "If he gave himself up they'd both be dead" with Ellis execution, John watched them take control of the hostages, watched them execute the Takagi, and when the first Terrorist thinks he's found John he shoots first after saying "I promise I won't hurt you" and then taking his bag and realizing how well financed and equipped, these guys weren't domestic terrorists, they used serious money, serious contacts, and serious planning to get themselves into this building on this night. He knew the only way to play ball with them was fists and elbows.
Just because a character doesn't do a thing I doesn't make it a plot hole. The plot was that he didn't do it. You may consider a different approach "better" but that's irrelevant. You may as well try to argue that any character choice that doesn't fit with a perceived meta is a plot hole. It isn't, it's just the plot.