Plot Holes
For the rollercoaster accident to happen, a combination of the hydraulic fluid from Lewis' restraints being forced to close, and Frankie's camera result in the fault with the restraints and the damage to the train and the tracks. As both Lewis and Frankie remove themselves from the rollercoaster before it leaves following Gwen's premonition, the accident should have been averted.
During the first flash back it is the camcorder that gets dropped and wrapped around the roller coaster track which sets things into motion for the whole tragedy. However after the vision when Wendy gets off the young lad with the camcorder gets off as well so therefore it wouldn't be dropped to cause the disaster.
Human is the most intelligent being on the planet