I was on a lift the rolled back. About 20 years ago in Revelstoke I was about 2 chairs from the top ramp and the lift stopped and slowly rolled backwards until I was about half way back to the bottom. The same lift had had a roll back in Whistler prior to being bought and move to Revelstoke. A quick thinking liftee jammed a steel I beam into the bullwheel and stopped it before anyone died. Totally fuct the bullwheel and badly damaged the drive carriage.