Revealing mistake: When the Welcome Wagon is being shot down you can see an explosion starting inside the last helicopter before it is even being hit.
Continuity mistake: When General Grey tells the President not to engage until they have visual, in the President's close-up the exterior of this F/A-18 Hornet is quite different than what was shown in the earlier shot, as the canopy closed over him. All the rivets around the canopy have disappeared and the 'danger' triangle is much closer to the name Patrick, the seat differs, etc. Plus the fact that the canopy and hull are actually one unit in the second shot. (02:02:15 - 02:03:15)
Visible crew/equipment: When President Whitmore returns to the containment lab to see the live alien, just as Major Mitchell and a Secret Service Agent walk to face the smoke filled lab, the actor's mark is visible on the ground as the Agent steps up to it. (Only visible on fullscreen DVD.)
Visible crew/equipment: At the White House, when they all watch the Soviet Special News, in the close-up of the TV's staticky reception of the news feed the reflection of White House staffers is visible. Right between the woman in a white blouse and the man in suit and tie, is the camera and crewmember, wearing a light-colored short sleeve shirt and baseball cap, moving about. (00:15:20)
Factual error: The Capitol's dome crumbles like stone, but it's made of iron. (00:48:10)
Factual error: When Steven Hiller is flying through the canyon he says "Hope you got an air bag" and pulls a lever to deploy the braking chute on his FA-18. The chute is then detached and lands onto the attacking alien craft. FA-18's don't have a braking chute, they rely on using an arrestor hook for carrier landings and a dorsal airbrake when landing on a runway. (01:00:50)
Visible crew/equipment: When David reaches Connie on her cell phone in the White House, as she walks away away from the wall to head towards the window, a crew member (complete with water bottle and utility belt) can be seen on the lower left portion of the screen, before he quickly scrambles away. (Only visible on VHS and fullscreen DVD.) (00:38:27)
Factual error: There is a shot of the Imperial Valley at night with the edges of the Los Angeles destroyer spinning over the mountains. The center of the destroyer is hovering over downtown LA. Imperial Valley is over 200 miles away from downtown LA, and the destroyer is no more than 20 miles in diameter. There would be no way the edges of the destroyer would extend far enough to be seen from Imperial Valley as shown unless it was over 100 miles in radius. The ship does not even hover over Steven Hiller's house which is in LA, it can nearly be seen whole from there. The destroyer would be obscured by the mountains and from 200 miles it would appear much smaller.
Continuity mistake: Several times during the last air battle, the President shoots his missiles, but a view of his plane shows that it still has all four missiles. (02:03:25)
Other mistake: When Connie is waiting for the President the first morning she is reading USA Today. On the back there is a weather map and it is blue and green, the colours for cold in USA Today. It was a hot July day! (00:06:15)
Continuity mistake: When David is looking for ice, the fridge door shelves are full of food. When Connie puts the bottle into the fridge, the door shelves are virtually empty. (01:24:55)
Factual error: When Jasmine is running in the tunnel, she kicks open the door just in time to save herself, her son, and the dog. The terrible fireball then goes right by them. They are just inside the open door, with fire and debris flying right past it. While the fire and debris might not spill in, the heatwave would still fry them. It is also likely that the fire would deplete the limited oxygen of the enclosed space. (00:49:50)
Factual error: David and Julius are traveling south to DC from NY so David can tell the President about the alien's plans. At one point, they're inside the city and the U.S. Capitol building is directly in front of them. This shot is famous because many movies have photographed the Capitol building from here. To get to this point in their travels they would have, in all likelihood, passed right by the White House since they are heading south on Pennsylvania Avenue towards the Capitol Building.
Continuity mistake: In the Area 51 hangar, when Steven and David are trying to take off in the alien attacker, we are clearly shown how the ship flies: Pull back on the controls, you go forward, push forward on the controls, you go in reverse. Later, in the mothership, after they have launched the nuke and are released, Steven pulls back on the controls, which should send them flying forward, but the external shot shows them flying backwards. (02:00:25)
Factual error: During the final battle over Area 51, Russell Casse appears in his F-18 and states he is armed. After he attempts to acquire radar lock on the alien's primary weapon, he states he is locked on and has tone. He then says the tactical brevity code Fox-2, which indicates the launch of an infrared-guided missile. However, the missile he is actually attempting to launch is an AIM-54 Phoenix, which is an active radar guided missile, designated by the launch code Fox-3. The master monitor display also incorrectly shows the missile mounted on the port wingtip launcher of the aircraft where the AIM-9 Sidewinder would normally be mounted, instead of on the port wing's weapon pylon where the missile actually is. Historically, the F-14 Tomcat was the only fighter capable of carrying the AIM-54, as it was such a heavy missile; the AIM-54 was never used on the F/A-18. Instead, they carry the AIM-120 AMRAAMs, not the AIM-54 Phoenix that were shown in the film.
Visible crew/equipment: In the containment lab, when the alien awakens and begins its attack, the alien moves from right to left towards a doctor, who is backed up against a door. The crewmember who is wearing the alien costume has on a white shirt and black trousers, and the costume's straps attached to the pants are visible, as well as some wiring at the back. (Only visible on fullscreen DVD.)
Continuity mistake: When the President holds his frightened daughter, in the shot after the alien craft creates a shadow over the White House, there are photographs and a bust of Lincoln on the table beside the President - the view of the photos is not blocked by anything. In the very next close-up of the photos, things differ, such as a large framed photo of the President with the Dalai Lama that appears out of nowhere, between the photo of the First Lady and the photo of the Pope.