AAIB Report G-EMEB, Gearbox failure during maintenance ground run, Aberdeen Airport

A failure of an alternator pinion roller bearing in the left accessory gearbox (LAGB) of an Airbus Helicopter EC175B (G-EMEB) occurred during a post-maintenance ground run following a scheduled replacement of the main gearbox. The investigation identified that the roller bearing was subjected to an excessive axial load during operation, caused by compression of grease and air within the alternator shaft link during installation by the operator of a 10 kVA alternator to the LAGB.

The cause of the incident was identified as the application of an excessive quantity of grease to the alternator pinion cavity, as required by the aircraft maintenance manual instructions. The method used by the operator to attach the alternator to the left accessory gearbox was identified as a contributory factor in the incident.

The manufacturer has amended the content of the aircraft maintenance manual to ensure that any excess grease is removed from the alternator shaft link cavity and has communicated this information by issuing a Safety Information Notice1 to EC175 operators.

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