Failure analysis of a bearing in a helicopter turbine engine due to electrical discharge damage

• Helicopter turbine engine failure due to the failure of the No. 2 bearing, due to electrical arcing prior to the accident flight.
• The bearings often provide electrical grounding between the turbine engine case and the rotating components.
• The morphology of the arced metal splatter deposits suggests that the arcing occurred when the engine was not operating.

This article documents the metallurgical evaluation of a rolling element bearing that failed due to electrical discharge damage. This rolling element bearing was used in a helicopter turbine engine that failed in-flight, resulting in a hard landing of the helicopter. Optical and electron microscopy as well as energy dispersive spectroscopy were used to evaluate the bearing. Pitting and material transfer on the external bearing races bearing and mating surfaces revealed that the electrical discharge damage occurred while the engine's components were not rotating.