Corrected entry: The Law of Gravity prevents the train from ever being stuck upside down in a loop; it's physically impossible. Also, coasters do not have brakes on the cars. The only moving parts on a roller coaster are the chain on the lift hill, and the brakes/brake release in the station. Once the cars leave the top of the lift hill, gravity is the only thing affecting the cars until they reach the station again. No electrical/hydraulic stuff on the cars at all.
Jazetopher
26th Feb 2007
Correction: The cars have been damaged by the camera, so it is plausible that a piece of metal acted as a braking device. Plus there has been an incidence in Switzerland where a rollercoaster has been stuck upside down for about 30 minutes, in addition another member was stuck in a coaster about 1 quarter up in a loop.
Ronnie Bischof