Failure analysis of the main rotor grip of a civil helicopter

This paper analyses the causes of a rupture which occurred with the main rotor grip device of a civil helicopter, which failed when the aircraft was attempting to land. From the visual examination of the fractured surface, it was possible to observe typical beach marks, thus indicating the occurrence of fatigue failure. Further examination, by using scanning electron microscopy (SEM) and metallography of the crack site, confirmed that the failure was caused by the mechanism of fatigue-crack initiation and growth from a corrosion pit located at the region of the blade retaining bolt hole.