Three equipment failures led to a rollback of a chairlift at the Sugarloaf ski resort in March, a memo from the state’s tramway inspector released Friday said.

The memo by John Burpee said a coupling connecting a high-speed gear and a low-speed gear failed on March 15, leading to gear teeth being ripped out on a drive shaft that delivers power to the wheel that pulls the lift’s cable. Then, Burpee said, an anti-rollback device failed, along with the brakes that were supposed to engage when the direction of the lift was reversed.

While the memo is not intended to be Burpee’s final report on the incident, he said the lift had a thrust bearing failure that was undetected and that may have contributed to the coupling failure. Burpee cautioned that the causes of the failures may not ever be determined conclusively, but he suggested ski resorts using similar lifts pay particular attention to checking those systems before the ski season starts this fall.

The lift rolled back 460 feet when the equipment failures occurred, injuring seven skiers. Some skiers jumped from the lift and others had to be helped to the ground by the ski patrol at the resort, which is located in Carrabassett Valley.

The memo issued by Burpee is intended to remind operators of similar lifts to review the issues he identified and make sure his recommendations for maintenance and inspections of the lifts are followed. There are similar lifts at the Sunday River and Big Squaw resorts, said Doug Dunbar, spokesman for Maine’s Board of Elevator and Tramway Safety.