Continuity mistake: After being violated in bizarre fashion, Janet slumps to the floor. Her dead body rests on the floor in a different position (arm on chest) just after. (01:05:10)
Character mistake: The very advanced computer on the plane can't spell, since it infers probabilities that a member of the crew has been "INFECTETED" by the creature. (01:06:40)
Factual error: When Don records the flight log, he says that they have been in the storm for 5 hours. That does not seem to match the timing of the events in the movie, but on top of that, it's a Vegas-Phoenix flight. That's a 250 miles distance that would take little more than one hour. (01:07:30)
Continuity mistake: The rich guy keeps putting stacks of money inside the briefcase, but it never fills up, with gaps appearing at the cut in spots he previously filled. (01:08:25)
Revealing mistake: When the alien creature stabs the rich dude in the skull, supposedly they are in the same room, but behind the xenomorph you can see a background that can't pass for the airplane cabin, looks like a danky cave. Recycled footage from another production. (01:08:35)
Continuity mistake: After the alien attack, the hole on the rich guy's forehead changes size between shots. (01:08:35)
Continuity mistake: Don and the others find the corpse lying face down into the money. The larger bloodstains are faithfully rendered from one shot to the next, but the bills and the actor's hand have changed position. (01:09:00)
Other mistake: The surviving lady is looking for Don who just killed Mike. There's a POV shot that pans from the dead Janet to the end of the room; it is obviously meant to be Rosie Malin's, but the effects used are the alien POV's, and she is not possessed (just yet). (01:18:30)
Revealing mistake: When the Alien-like creature chokes the gambling lady with its tongue, the woman has no strangling marks of any sort on her neck. (01:19:10)
Revealing mistake: When the two survivors get in front of the emergency door, their hair gives out all sorts of chromakey artifacts. (01:21:00)
Revealing mistake: In the final explosion, the plane loses two of its engines, or rather, a bad superimposed image of each engine that fly at the screen. (01:21:30)
Other mistake: Mike sabotages the parachutes...of which there are exactly four, like the number of survivors. A bit scarce for a Boeing with a staff alone double that size.
Plot hole: Everyone is by Jack to try to help with the alien monster up his nose. By "everyone" we include the pilot and the copilot. Throughout the rest of the movie they wander about plenty times, both at the same time. The automatic pilot was knocked offline by the storm, and as Bob mentions in a later conversation, it was never fixed. So, who is driving the plane? Rhetorical question.
