Failure analysis of MGB housing of a helicopter

The mounting lug of the MGB housing of a helicopter has failed by fatigue. With the available evidences, it was not possible to establish the exact cause of the failure. Analysis shows that the fatigue crack initiation was due to one or more of the following reasons: (a) ovality in the lug bore and/or bush, (b) excessive rotational torque on the MGB housing, and (c) improper fitment. No metallurgical abnormalities were responsible for the failure. The microstructure and chemical composition of the housing material were found to conform to RZ-5 specification