MINNEAPOLIS - Giant brake pads were slowing Valleyfair's Wild Thing roller coaster when the last of its six cars broke away and lurched to a tilt, sending 15 riders to the emergency room.
Those brakes of the signature ride at the Cedar Fair LP-owned amusement park in Shakopee, Minn., will be under scrutiny as the owner, the manufacturer, and outside engineers try to figure out the cause of Sunday afternoon's accident.
At the time of the accident, the ride "was well into the brakes, so probably that's going to be significant once we can get under there and see it," said Tip Harrison, director of Valleyfair's physical plant.
Though he would not speculate on what the investigation might reveal, Mr. Harrison doubted such an accident would have happened anywhere else during the ride.
Valleyfair officials inspected parts of the ride yesterday but did not physically touch anything.
They were waiting for officials of the ride manufacturer to arrive by plane from California.
No government agency will investigate. Some states inspect amusement park rides, but Minnesota leaves that responsibility to the park owners and their insurance companies.
The investigation is expected to take days, Mr. Harrison said.
Mr. Harrison said the rear wheels on the second-to-last car came off the track and broke away from the car. But he didn't know whether the derailment had happened before or after the cars separated.
Valleyfair would not release its safety record because its insurance company will not let it do so, Mr. Harrison said, but national amusement officials tout the safety of rides in general.
At Valleyfair inspectors hired by insurance companies inspect the rides once a year before the park opens.
Valleyfair has its own staff of inspectors who graduate to various types of rides based partly on experience, Mr. Harrison said.
Many go through the same training as government inspectors from other states. One of Valleyfair's staff teaches at the training sessions.
The accident occurred a day after the ride was stopped twice because computerized sensors had detected something.
Both times, maintenance checked the ride and found no problems.
Mr. Harrison said those shut-downs were caused by false alarms that were unrelated to the accident Sunday.
Mr. Harrison has been the park's physical plant director for 28 years.