What happened
On 28 December 2016, a Sikorsky S-92A, registration G-WNSR, was performing a scheduled flight to the West Franklin wellhead platform in the North Sea. During the initial phase of the flight from Elgin PUQ, the aircraft experienced an uncommanded yaw event immediately upon lift-off. The crew subsequently proceeded to the West Franklin platform, where the aircraft landed.
The investigation
Investigators examined the aircraft's flight data and the Health and Usage Monitoring System (HUMS) to reconstruct the sequence of events. The investigation focused on the mechanical integrity of the tail rotor pitch change shaft (TRPCS) and the tail rotor servo. Physical examinations of the wreckage and components at a maintenance base were conducted, including an analysis of the TRPCS bearing and the tail rotor gearbox. The investigation also reviewed maintenance records, specifically looking at oil sampling history and the implementation of recent service bulletins regarding temperature indicator plugs.
Findings
- The aircraft experienced a sudden, uncommanded yaw during the takeoff phase from the Elgin PUQ helideck.
- The investigation identified a failure within the tail rotor pitch change shaft bearing assembly as a primary factor.
- There were concerns regarding the adequacy of the vibration health monitoring (VHM) data timeliness and the processes for downloading and analyzing HUMS data.
- Maintenance-related factors, including the management of prospective memory by engineering personnel and the monitoring of bearing lubrication, were evaluated as contributing elements to the overall safety environment.