AW139 Tail Rotor Duplex Bearing Failure

A serious incident was identified during maintenance of anAW139 helicopter involving failure of a tail rotor duplex bearing, a criticalsafety component.

The failure was detected after flight during inspection, not in-flight.

The extent of damage showed that continued operation wouldlikely have caused loss of tail rotor control. The root cause could not bedetermined due to severe damage.

Safety Recommendations

1. Introduce a comprehensive inspection and sampling programmefor bearing including both serviceable bearings and failed/removed bearings. Tovalidate reliability assumptions and understand failure mechanisms.

2. Use HUMS data to monitor pedal position trends in stableflight to detect early degradation of bearings.

3. Develop capability to monitor vibration of duplex bearingon AW139.

Immediate Operational Actions

Ban on refitting bearings after removal. Reduced life limitfrom 3,000 - 2,400

flight hours. Mandatory removal of refitted bearings andhigh-life bearings (>2,400

hours). Frequent checks introduced for rotation “slip marks”on actuator shaft, bearing condition inspections and increased inspectionfrequency for some bearings.

Regulatory Actions

Emergency Service Bulletins (SB) and EASA AirworthinessDirective (AD) mandating corrective actions.

_{Photo Source: Kolforn Wikimedia Creative Commons 4.0}

‍