Continuity mistake: When they run onto the roof near the start, there's another trooper behind Harry running onto the roof (only visible in widescreen - in 4:3 it looks like a weird reflection). In the following shot of Keanu Reeves you can see the reflections of Harry and the other guy on the plastic covering the scaffolding. We're led to believe that Harry and Jack should be the only ones up there, as everyone else has a job to do. Aside from those two shots, this third trooper disappears once they start hooking the crane up. (00:11:30)
Visible crew/equipment: When the police officers are attempting to rescue all the passengers on the bus while at the airport by driving up beside the bus, at one point you get a front camera angle shot showing the people jumping out of the bus onto the police vehicle. If you look closely, you can see the camera man sitting on his chair reflected in the window of the open bus door, he is wearing a white shirt with sunglasses.
Character mistake: At the airport, when Jack is under the bus on the trolley being towed by the truck, an accident causes all the cable on the winch reel to pay out. At this point all that's holding the cable to the reel is a small metal clamp. Jack slews around under the bus for a while, in grave danger of being run over by the vehicle's rear wheels, and then the clamp gives way (in slow motion). The now-free cable shoots toward the bus, and Jack pulls himself off the trolley just as it goes under the rear wheel. If you look at the shot where the cable is flying toward the bus, you can see two SWAT guys standing on the back of the truck, on either side of the winch. Their posture is completely relaxed and casual. Considering that for the past several seconds, Jack has been sliding around under the bus, fighting for his life, wouldn't the SWAT guys be much more excited--moving around, trying to get a better look, giving instructions to the truck's driver?
Factual error: If you look at the loop Keanu hooks the crane onto on top of the lift you can see that it and its bracket have been recently welded on (by the black residue it leaves), obviously because the lift itself didn't have such a loop. Even if such a feature existed, it wouldn't be simply spot welded on the top as this one is, it would need to be part of the lift's structure if it were to serve any purpose in supporting it in an emergency. (00:13:05)
Factual error: At the airport, Jack attempts to disarm the bus bomb from underneath, on a dolly towed by another vehicle. Meanwhile, Annie must continue driving the bus in circles on the runway at a speed above 50 mph. This scene takes 8 minutes, meaning Annie makes at least 2 laps of the entire 2-mile-long runway, complete with turns at the ends. There is no way that the towed dolly could remain positioned directly underneath the bus through the turns, as Jack would have swung out under centrifugal force.
Other mistake: As the first bus explodes on its way from the cafe, we can see a blonde pedestrian casually walk past a window with her ears covered. At no point does she even stop to glance at the burning wreck. It seems (from her perspective) as though the explosion were merely an inconvenient loud noise and nothing worth noticing. (00:27:55)
Other mistake: Towards the end when Dennis Hopper is on the subway train with Sandra Bullock, he has a gun in one hand and the detonator in the other. However, when the camera cuts to a close-up of him handcuffing Sandra to the pole, both hands are empty. If he took his hand off the detonator, the explosives attached to Sandra should've exploded, but they didn't. In the next shot, both items are back in his hand. (01:39:50)
Revealing mistake: When the train is sliding along the ground near the end, there are sparks coming from the underneath (supposedly where the metal scrapes the pavement). Look more closely, and you can see that the sparks are coming from a bit of the train that's not touching the pavement anywhere. (01:44:55)
Continuity mistake: After Keanu commandeers the civilian's car, breaks off the door and jumps to the bus the civilian loses control and heads for the water barrels in front of the divider. Right before he hits you can already see water all over his windshield. (00:38:20)
Factual error: When the bus jumps the gap in the freeway, the front wheels rise into the air while the rear wheels are still in contact with the roadway (that has a very slight upward slope). Since its trajectory is fairly flat in the movie (unlike the ramp used to actually film the stunt), the front of the bus would fall well short of the other side. Further, the impact of landing would render the bus unable to move (which is exactly what happened to the bus used to film the stunt). (01:03:40)
Factual error: The bomber demanded his money by 11 a.m., so the sun should be high in the sky toward the end of the bus situation. However, in many shots at the airport, there are long shadows, indicating either sunrise or sunset.