Failure of an Inclined Elevator

Abstract

The failure and crash of an inclined passenger lift are examined and the probable cause together with a likely sequence of events is arrived at. This failure was in two parts; initially the gearbox output shaft suffered a fatigue failure, freeing the winch drum from the motor and normal brake. This was followed more importantly by the malfunctioning of the emergency brakes on the lift, allowing the lift to roll to the bottom of the run. The lift had been upgraded prior to its failure. Calculations show that the gearbox output shaft that failed was more than adequate for the loads imposed on it by the new controlled motor, whereas the original direct-on-line motor probably had overstressed the shaft. The steel lifting rope exhibited three severe kinks about 1 1/2 m from its attachment to the trolley. The search for the causes of these kinks led to the discovery that a lever mounted on the emergency brake shaft had been damaged and bent. Evidence came to light that the whipping action of the rope, following the release of the winch drum after the shaft failed, relocated the lifting rope under the lift cabin and over the safety equipment on the trolley. This abnormal location of the rope placed it in a position where it interfered with the movement of the lever and hence with the rotation of the emergency brake shaft. With this shaft restricted in its rotation the emergency brakes failed to apply properly.