by Matthew Beres, Airborne Retrofit & Modernization Analyst, Forecast International.
The United Kingdom’s Air Accidents Investigation Branch (AAIB) has released a Special Bulletin regarding an S-92 accident on December 28, 2016, at the North Sea’s West Franklin wellhead platform.
The initial investigation focused on the tail rotor and its components. Immediately, it became apparent that the tail rotor servo piston was damaged. Removing the servo revealed the tail rotor pitch change shaft (TRPCS) double row angular contact bearing to be in a severely distressed condition.
Here’s a breakdown of what happened:
Here’s a breakdown of what’s being done:
The Operator will:
- Review all HUMS data to ensure no anomalies
- Provide fleet-wide borescope inspections
- Require HUMS to be serviceable before flight
- Reduce time between HUMS download/analysis to a five-hour maximum
Sikorsky will:
- Provide a one-time inspection of the TRPCS and bearing assembly for ratcheting, binding, and rough turning
- Compliance is essential and is to be accomplished prior to the next flight from a maintenance facility
- Enforce a three flight-hour limit before return to a maintenance facility
- Require operators under Temporary Revision 45-03 to use S-92 HUMS ground station software to review Tail Rotor Gearbox energy analysis Condition Indicators for alert conditions on a reduced flight-hour interval
- Records in excess of published alert levels will require inspection of the pitch change shaft and bearing
Both the AAIB and Sikorsky are continuing to examine the accident, including the relevant helicopter components. More details will be provided as information becomes available.
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