Electric discharge damage in aircraft propulsion bearings

Rolling contact fatigue (RCF) is a common failure mode for rolling element bearings, however evidence of precursor failure modes or initiators can be lost or obscured by the subsequent severe damage caused by RCF. Although electric discharge damage (EDD) is not normally associated with rolling element bearings in aviation propulsion applications, it can occur and may not be instantly recognisable. Unlike factors such as lubricant cleanliness or misalignment, EDD does not normally form part of the life prediction of aviation propulsion rolling element bearings. Early identification of EDD and subsequent mitigation or elimination is, therefore, essential to prevent significant reduction in life or failure of rolling element bearings. This paper will review the phenomenon of EDD and discuss several recent examples observed in aviation propulsion systems.