MEDIA ADVISORY: Sugarloaf Rollback Investigation Reveals Apparent Lift Design Issue
CARRABASSETT VALLEY, ME - A team of investigators, including Sugarloaf personnel and engineers from Boyne Resorts (Sugarloaf's parent company), have completed a preliminary review and investigation of the rollback of the King Pine Chairlift on Saturday , March 21, 2015.
Investigators determined that a fracture of the main drive shaft of the lift's secondary gearbox initiated the rollback, and that the lift's bullwheel brake engaged and operated properly.
Investigators also identified an apparent manufacturer design issue in one of the lift's components as contributory to the accident.
Sugarloaf and Boyne engineers have also identified a retrofit for the system that corrects the issue.
"Our first thoughts remain with those injured, and our sincere hope is for their speedy recovery," Sugarloaf General Manager John Diller said. "I'm grateful that we now have a clearer understanding of what occurred."
Gear Box Failure:
The incident on King Pine occurred at approximately 11:30 Saturday morning, when a shaft in one of the two gearboxes that transfer power from the lift's electric motor to its bullwheel fractured.
The gear boxes in the King Pine lift, along with every other lift at Sugarloaf, were subjected to a routine vibration assessment by an outside contractor the day before the incident, and no anomalies were detected that indicated such a fracture was imminent or likely.
The fracture of the shaft resulted in the loss of both the primary service brake and the anti-reverse brake, leaving two additional braking systems intended to prevent a rollback.
The failure of the shaft, in and of itself, should not have resulted in the rollback that occurred, if the lift's remaining systems had performed as intended.
Bullwheel Brake Activation:
Though further investigation is still needed, findings suggest that an automatic system to activate the lift's bullwheel brake (identified as "emergency brake" in previous statements) activated properly. Additionally, the lift's operator quickly activated a manual control to apply the bullwheel brake.
Bullwheel brake activation is, by design, not instantaneous, because an immediate stop of a moving lift can create sudden and dramatic movement along a lift's haul rope, potentially causing enough movement to cause skiers to fall out of chairs, a deropement of the lift, and other significant damage.
In the time between bullwheel brake activation and the actual stoppage of the lift, the lift traveled backwards for a total of nine chair lengths, or approximately 460 feet, due to the weight of skiers on the lift, which was full.
The investigators also found that a further system to prevent a rollback failed, due to an apparent design flaw.
The Drop Dog:
The final system intended to automatically engage to prevent a lift rollback is commonly referred to in the ski industry as a "drop dog." Lifts are required to have some form of device to prevent the lift from counter-rotating, and variants of the drop dog approach are generally used today.
The investigation revealed that one of the switches used in the safety circuit connected to the drop dog was an inappropriate switch for the intended application. This switch, which is designed to suspend the drop dog above the bullwheel when it senses forward rotation of the lift, can also suspend the drop dog when the lift rotates in reverse.
This switch was provided by the lift's original manufacturer, and is still provided by the company that manufactures components for this type of lift.
The investigation indicates that, had an appropriate switch been included in the system, the drop dog would have deployed and the rollback would have stopped immediately.
Sugarloaf personnel and Boyne Resorts engineers have designed circuitry to correct this situation. This modification has been reviewed and approved by a licensed Maine lift inspector, and is being installed on other lifts at Sugarloaf that employ the same type of switch.
There are six such lifts at Sugarloaf - Skidway, Sawduster, Snubber, Double Runner East, Double Runner West, and Bucksaw. Upon reaching the above conclusions regarding the drop dog switch this morning, and acting on an abundance of caution, Sugarloaf personnel made the decision to temporarily shut down the Skidway, Sawduster, Snubber, and Double Runner lifts until the modification was installed. The Bucksaw lift was not scheduled to operate today or tomorrow and will be modified before it is operated again on Friday.
Sugarloaf and Boyne Resorts have been in touch with the lift's parts manufacturer to share their findings.
The investigation of the incident by the State of Maine Board of Elevator and Tramway Safety (Tramway Board) is ongoing.