Factual error: At the end of the film Rainwood has established his innocence of the drug charges and is happily back at work as a senior mechanic for a large airline. However, part of the sentencing and plea bargain protocols at his arraignment is his previous conviction on a lesser drug charge years before. It goes without saying that he did not advise his employers of this when he started work for them - no airline in the world (even pre 9/11) would hire someone with a drug conviction on their record! Now this is out in the open the airline knows that Rainwood is a convicted drug user (on the lesser, legitimate charge) and that he lied on his original job application. They wouldn't hire him again to sweep the floors.
Other mistake: Sergeant Johnny Gallagher (Gene Hackman) and Lieutenant Milon Delich (Dennis Franz) are in a supposedly deserted building searching for a group of conspirators who plan to assassinate both the USA and USSR presidents. Delich finds a police colleague of his in the building, and Delich kills his colleague. When he fires his revolver, the sound of the blanks can be heard, slightly out of synch with the gun blasts on the sound track.
Continuity mistake: In the scene where Belushi and Jerry Lee (the dog) enter the warehouse, Belushi askes everyone to stop what they are doing and even has the forklift driver lift him up so he can talk to them. Once he is done talking, he tells the lift driver to bring him down. The next few shots where they show Belushi walking to his car, if you look closely, you will see that the fork lift is back up in the air, but there were no sounds and there isn't another lift to be found. (00:25:05)
Continuity mistake: Towards the end of the movie Dave takes Walley's jacket and uses it to help them slide down a cable. Before they slid down, Dave tells Walley to hold on, and Walley asks if they're going to be above the ground. Dave tells him no, and off they go. However, Dave is deaf, and reads lips, and Walley is standing behind him when he asks the question. So how did Dave read his lips if he wasn't looking at him?
Continuity mistake: When Harris is briefing the new group for the first time, Hightower loosens the leg of Harris' chair so that it breaks when Harris sits down. When Harris gets up from the middle of debris, the next shot shows an innocent looking Hightower and the chair is intact in front of him.
Continuity mistake: In the scene where they are discussing why Dalton fired Mr Wesley's nephew (upstairs in the Double Deuce). Mr Wesley's nephew threatens Dalton with a knife and when Dalton takes a swing at him, there is blood on Mr Wesley's nephew's face way before contact. (00:34:05 - 00:38:00)
Factual error: While Fletch is riding with the bikers, they stop at a stop sign where a family in a station wagon roll up their windows in fear. A sign at a service center in the background is the Castaic Junction, which is in the greater Los Angeles area. The movie is supposed to be taking place in Louisiana. (01:12:35)
Continuity mistake: During the big fight scene at the end of the movie, both Nick and Sato become totally saturated and covered in mud. Nick defeats Sato, and is shown to have immediately arrested Sato and brought him to the police station. It is clear they came directly to the station from the fight, yet there is now hardly any mud on either of them.