During the gymnastics scene, there is a vaulting table in the background. The movie is set in 2000, when the old vaulting horse would have still been in use. The vaulting table wasn't used in NCAA gymnastics until the 2002-2003 season.
The news reporter says that there were eight employee bus survivors and 17 employees who died on that bus. When Isaac gets up to talk in the restroom, you can count the number of employees, and there are only 19.
(at around 17 mins) In the premonition, we can see that the pickup carrying iron rods has begun to fall in the bridge gap and dropped some of its contents. In the Real the pickup remains safely away from the gap in the bridge.
In the Final Destination 5: Circle of Death special feature it is said that some of the actors from the first _Final Destination (2000)_ were brought back to film the airplane scene but this is incorrect. Their footage was actually green screened into the film.
(at around 32 mins) During the gymnastics scene, there's a girl doing a routine on the uneven bars. There's a thick blue pad that she dismounts onto and an orange mat next to it. A few minutes later when Candice is doing her uneven bar routine the blue pad and orange mat are gone.
(at around 13 mins) During Sam's premonition the bus driver can be seen instantly going from standing up to sitting down between shots several times while everyone is evacuating the bus. Eventually, just after Candice's death, the driver is sat back down in his seat again, but in the very next scene the bus is seen to be completely deserted apart from Isaac.
(at around 15 mins) During the bridge collapse, there is a gap between two rail pipes that Molly and Olivia try to cross. When Olivia attempts to cross the two railings following Molly, she is seen on the first railing crawling and looking at Molly reaching for her. In the exact next screen shot, Olivia is seen on the second railing reaching or Molly, then falls.
(at around 14 mins) In the bridge sequence, the bus free falls with a passenger inside, who was initially in the back. The movie shows the man falling towards the front windshield during free fall, but in reality, the person would feel weightless, and float inside the bus, since both the person and bus were in free fall at the same time.
(at around 1h 18 mins) In the kitchen scene, there are two large bottles for the fire suppression system on the wall. When Peter shoots one of the bottles, gas comes spraying out. Restaurant systems do not use gaseous suppression agents, they use either liquid/foam or dry chemical agents. Because in principle they rely on displacing enough oxygen in the room to starve the fire, gas systems are ineffective against 'localized' grease fires - in addition to being potentially lethal to anyone in the room when discharge occurs. They are only used in areas where fires would be electrical in nature and dry chemicals or foams would cause collateral damage to sensitive equipment (such as computer rooms).
In the final aircraft scenes at approx 83 mins, external shots show a Boeing 747, a wide bodied twin aisle passenger jet. Internally, we see Sam and Molly at the back of a smaller, single aisle passenger jet with a 3-3 configuration. They are sitting in row 23, one row before the back of the aircraft. The back rows of any 747 can number as far as the 70s, with a 2-4-2 configuration at the very rear. His assigned 23J seat (as seen on the boarding pass) would be somewhere else.
The spanner/wrench that killed Dennis changed from a shiny combination type (open-ended one end, 12-sided ring the other) to a matt black box-type between the time it fell into the running belt-sander and flying through the air to the shot of it embedded across, and into, his forehead when lying dead on the ground.
(at around 34 mins) The screw on the balance beam would not have gone unnoticed by any of the gymnasts or the coach. Additionally, no coach or team member would ever permit an electrical cord, or a cord of any kind, across the mats.
(at around 14 mins) In the foresight scene on the bridge, the bus obviously falls into the water before the whole bridge collapses, but in the reality the bus can be scene falling with the entire bridge in the distance.
(at around 51 mins) Although heavy and high up the Buddha that fell on Isaac's head may have had enough force to crush his skull but not enough to completely flatten his head and it would not shear and sever the arteries and skin of his neck.
(at around 1h 18 mins) In the kitchen when Peter shoots the large cylinder mounted on the wall near the gas stoves, the cylinder should have contained a fire suppressant chemical which would have made it hard to breath. Yet the entire time the cylinder is spewing its contents into the kitchen, not one of the people present even so much as coughs.