Continuity mistake: During the battle at Lerner field, Poe drives a burning police car from the boneyard and leaves it right at the ramp at the rear of the plane, and then ties the plane up to the post. When the plane goes to take off and Cyrus sees the plane is tied up, the burning police car is nowhere to be seen.
Continuity mistake: In the final chase scene at the end of the film where Poe and Grissom are fighting on the ladder of the fire truck, and Poe handcuffs Cyrus to the ladder rail, Poe activates the ladder causing it to raise....this is not possible. The transmission of fire apparatus do not permit aerial ladders to be operational while the vehicle is moving. (01:43:20)
Continuity mistake: Colm's car gets hooked up to the plane and then, after crashing into the watchtower, falls to the ground. If you watch the shots of the car falling you can see John Cusack's arms go from folded to at his side multiple times. You never see him move them, they just appear to have changed positions. (01:28:35)
Continuity mistake: When Diamond Dog puts the hat on in the plane after it's hijacked, he puts it on backwards.A second later, it's on straight without him turning it around. (00:43:55)
Continuity mistake: When the plane is crashing into the hotel, it crashes into a white corvette. Then it cuts to another scene, then it cuts to back outside, and you see the plane crash into the corvette again, from a different angle. Then it does the same thing 2 more times, until the plane is actually stopped. After it cuts to another scene outside, you see the same corvette, with only a flaming piece of metal on the hood, not completely shattered like it should be. (01:37:30)
Continuity mistake: When Cameron and Diamond Dog go into the belly to inspect what's wrong with the landing gear, Cameron flips a switch to turn on the lights on the floor of the belly. When he does this, you can see a lot of boxes between the landing gear and the ladder that him and Diamond Dog climbed down. But, as they head to the back to look at the landing gear, all the boxes are now gone.
Continuity mistake: In the extended edition, after Johnny attacks Guard Bishop and is stopped by Cameron, the cons run back to the plane to escape, and all of a sudden Johnny appears from nowhere with a gun and is shot, when he was just on the plane being beaten up by Cameron, and is then shown being put in chains by Cameron back on board the plane.
Continuity mistake: When Pinball leaves the plane, he opens a door under the cargo hold, and he never makes it back on the plane, but when the plane is taking off, that door is now closed. (00:43:00)
Continuity mistake: The last shot of the plane as it's taking off from the runway with Malloy's car attached to it is a flipped shot. Notice the logo and Jailbird writing near the nose of the plane are backwards.
Answer: If there was ever an emergency landing the weapons would be needed with the prisoners as they most likely will have to exit the plane at some point. There doesn't seem to be any information around that says that every prisoner transport plane would have the same amount of weapons or in the same spot but it seems likely most would have backup weapons for situations like that.
Lummie