There are three spots where a Vekoma Boomerang can be predicted to stall: In the station, in the saddle between the two Sidewinder inversions, some 40' in the air, and at the base of the second lift , between the lift and the vertical loop. This is why there are brakes at the base of the second lift: as the train is hauled up the second lift, the brakes are kept closed until the train gets high enough to clear all three inversions...that way if it breaks loose prematurely the brakes will bleed off enough energy to prevent the train from going through the vertical loop, so that it will just roll back into that valley. A similar tactic is used on the other side with the station brakes.
One thing they didn't consider, though. There is no roll-axis pivot on the connection between the train and the catchwagon. Now here's the problem. The train gets high enough up the first lift for the station brakes to open, but not far enough to release the catchwagon. Suddenly, the lifting cable breaks, and the train...with the catchwagon still attached...barrels down the hill and through the station. It makes it up the hill and the train goes through the sidewinder inversion. But the catcwagon can't roll relative to the rest of the train. The forces attempt to twist the locking mechanism into a pretzel shape, but it just isn't malleable enough. The last axles...the train's back axle and the catchwagon...jam tightly enough that the train can no longer move forward past the twist at the top of the inversion. Furthermore, with the entire weight of the train pulling forward and down out of the inversion, there is no way that this thing is going to spontaneously go backwards. Result?
The last car or two are stuck, inverted or nearly inverted, at the top of the Boomerang element. Whoops!
On the Demon, the best information I have says that they dropped the last axle off of the train, allowing the back end of the car to function as a giant combination of skid brake and anti-rollback. The friction of the car dragging against the track would slow the train enough to keep it from completing the loop, and when the back end of the train drops and hits the track tie, that keeps the train from rolling backwards out of the loop.
Finally, the Schwarzkopf shuttle that got stuck upside-down. As I understand it, there is a pusher-plate at the back of the train, normally high enough that it will clear the track-ties. But in the loop, it is close enough to catch. Normally that plate is weighted to stay clear of the track except in the station...but going too slowly through the inversion, it drops (since the train is inverted), and can catch on the loop track tie, preventing the train from rolling backwards after it fails to complete the loop.
It's worth noting that since the Demon incident, Arrow has modified their looping coaster trains, adding a safety bracket to prevent the last axle from separating from the train even if the attachment pin fails. The other axles on the train were already backed up.
--Dave Althoff, Jr.
