A man witnesses a gangster (Eddie Kim) kill a prosecutor who had tried several times to send Eddie to jail. The witness is then convinced to testify against Eddie. The murder occurred in Hawaii, and they have to fly to LA. Snakes are in the cargo hold on a timed cage (apparently security didn't catch them because they are cold blooded) and were, of course, placed there by Eddie Kim so that the witness would not survive. The first people to die are a few kids joining the mile high club and one of the pilots. Then snakes start coming from everywhere and the passengers have to fight them off/barricade themselves from the overly aggressive snakes. The second pilot ends up dead and a man with experience flying planes on his PlayStation2 ends up landing the plane safely.
Plot hole: The snakes escape from the locked box stored in the cargo hold when a small explosive bolt detonates and opens the lid. Post 9/11 all luggage placed in the cargo hold of an airliner would be tested for explosives, and anything larger than half a match head would be detected. The chances of getting an explosive bolt on board - nil. None whatever. You can also think of it this way - if the bad guys could somehow smuggle explosives on board, why bother with such an elaborate and flawed plan as letting snakes loose on the plane? Why not just smuggle a bomb on board? Pan Am 103 - the so-called Lockerbie flight - was brought down with a bomb that fit inside a small cassette player.
Trivia: The poster for this movie features two snakes wrapped around a plane in a double helix style, with the film title across the middle, However some posters feature the same snakes/planes but with the title underneath. Take a closer look at this second type of poster and match each snake's head to its tail. if you match the right snaked head to the left tail the other snake head doesn't match up to the tail. Try this in any combination you like, ie. left head/left tail or right head/left tail. You will always be left with a head not matching a tail.