Continuity: Wine glasses are still standing after a deceleration powerful enough to throw people around.
Revealing mistakes: When the second stealth bomber explodes after being hit, the model of the bomber can still be seen clearly swinging on wires at the top of the shot.
Audio/visual unsynchronized: When the bad guys are loading the equipment on the train, one of the bad guys says, "trouble in the dining car, one casualty." But his voice obviously doesn't match his mouth.
Continuity: When Travis Dane is "posing" to be in France, the live feed is stopped and the screen goes black. A shot of the crowd watching the now-black screen shows a window which is reflecting an image of the screen with Travis Dane still on it.
Factual errors: While Ryback is hanging on the rope, the porter takes a few pot shots at the terrorists. Prior to shooting he says, "Safety off". Glock handguns do not have a safety that can be switched on or off. It is integrated into the trigger assembly and turns 'off' as the trigger is depressed.
Continuity: When Ryback is driving in the truck to get back on the train, his car windows are open. When he drives through the water, the windows are closed, but they are open agin in the next shot.
Continuity: After recovering the CD from under the train, Penn says to Sarah, "Guess your uncle wasn't that good after all." But none of the bad guys has yet established the exact connection between Sarah and Casey, except that Sarah is traveling as Casey's '+1' on the passenger manifest.
Continuity: When Ryback is hanging from/standing on the cliff after the train stops, a close-up shot shows both of his feet together on one small ledge. A long shot about 10 seconds later shows his feet on separate rocks.
Crew or equipment visible: Rotor blades of chase helicopter visible when Hueys are leaving the National Guard base.
Continuity: Penn is wearing a leg holster for his walkie-talkie through most of the movie, but at the knife fight (and just prior to the fight) it's gone.
Continuity: When Penn slips the noose around Sarah's neck, it's tied off with a knot. In the very next shot the end is crimped on with a metal clasp, no knot visible. It changes back and forth several times after that.
Revealing mistakes: When the train slams on its brakes, you can see a spark generator in front of the wheels.
Continuity: When one of the guys leaves the locomotive to look for Casey, someone else takes his seat. In the next shot, the "seat-stealer" is back to where he originally was.
Continuity: In the ATAC control room before the two captains enter their passwords to gain control of the satellite, the screen with the asterixed-out passwords which appears after the transfer is completed is visible.
Revealing mistakes: As the train pulls away after it is captured, a view of the rear car of the train not only shows no corridor door, but also the interior of the car is an empty shell mockup with no interior.
Continuity: After the capture, the train starts to pull away with a shot of the locomotive moving off. The very next shot of one of the helicopters taking off however shows the train in the background not moving.
Revealing mistakes: Shortly after attempting to send the fax from the payphone, Casey is seen pulling a dead mercenary through a door by his arm, shortly before another mercenary comes down the stairs. Casey grabs the dead guy's left leg to pull it, but both legs move together as the actor moves them himself.
Continuity: The spotlights behind Travis Dane during the "Paris Feed" disappear when he is on screen at the command center. However, by the staging of the spot lights on the back drop on the train, the lights should be visible to those in the command room.
Audio/visual unsynchronized: When Herb, one of the Mercenaries threatens to kill a child, his mouth is closed, but you still hear his line.
Factual errors: Once they realize that the person they are looking for is Casey Ryback and a Navy Seal, one of the terrorists tells the group that Ryback was his instructor at Fort Bragg. While this is home to Army Special Forces and Delta Force, it is not a normal training ground for Navy Seals.
Plot holes: Satellites in orbit around earth are radar tracked by multiple ground stations. It is therefore impossible to "lose" a once known satellite as depicted in the movie (especially for the US military). This completely obliterates the plot's preconditions.
Revealing mistakes: When the mercenaries break into the air base, the wire fence perimeter that is visible in long shot completely disappears in the following shot when the bad guy presses the keypad to enter through "the gate". The gate is suddenly the only section of fence left remaining, meaning he didn't have to enter a code and could have just walked around it.
Continuity: The number of locomotives on the Nevada Petrol Express.
Errors in geography: At the end of the movie, the Grand Continental crashes into the Nevada Petrol Express, which is being pulled by Southern Pacific diesel locomotives. The Southern Pacific RR never ran in Colorado.
Revealing mistakes: When people are walking on, or hanging on, a moving train, none of the clothes move in the wind.
Revealing mistakes: It is absolutely impossible, even for trained people, to keep your hands behind your heads for hours and hours. Yet this is what we see with the hostages in the train whilst the action goes on.
Revealing mistakes: When Ryback kicks a terrorist off of the front of the moving locomotive, it's an obvious dummy landing on the tracks when seen from the high wide-angle shot.
Miscellaneous: The actual credits for this movie show that Dale Dye played Col. Darza. This is incorrect in more than one way. Not only does Admiral Bates call him Captain Garza in the movie but his character is a continuation from the first Under Siege (1992). On a more factual basis, Colonel is not a naval rank and as Garza is a direct subordinate of Admiral Bates it means he must also be in the navy.
Revealing mistakes: In the final fight Seagal and the mercenary roll down the stairs fighting. You can only see the back of his head but this clearly isn't Seagal. The hair of the stunt-double is dim and short, not shiny and combed like Seagal.
Factual errors: When the shuttle releases the satellite the PBDs (payload bay doors) are partially closed. Shortly after achieving orbit the PBDs are fully open to release built-up heat in the cargo bay, and the doors are generally not closed before re-entry, as well as being fully open during deployment/retrieval of satellites.
Continuity: When Casey sends the fax, he is seen signing his name in cursive. When the fax arrives at the restaurant, there is no signature.
Audio/visual unsynchronized: When Casey is on top of the train car looking at the terrorists through a window on the edge of the roof, Travis Dane says "300,000 pages of code. Or 60 minutes of triple-X rubber-and-leather bondage porno.", his mouth is clearly not moving.