What happened
At approximately 12:38 PDT, a Sikorsky S-76A helicopter departed from the Vancouver Harbor helipad, carrying two pilots and eight passengers. The flight was destined for Vancouver International Airport. As the pilot began decelerating for the landing, a high-frequency vibration was felt through the collective pitch lever. While the intensity of the vibration decreased as the pilot maintained minimum power, a secondary, low-intensity vibration was detected in the tail rotor pedals during the final phase of the approach. The pilot opted for a no-hover landing and successfully taxied the aircraft to a hangar. There were no injuries and no damage to the aircraft.
The investigation
Maintenance personnel identified the source of the vibration as a broken tail rotor pitch control rod assembly. An analysis by the TSB Engineering Branch determined that the failure occurred in the rod end of the assembly. The investigation revealed that the failure was caused by high cycle fatigue occurring under normal service loads. This fatigue was linked to stress concentrations at the thread roots, which were further exacerbated by the presence of corrosion pitting.
Further examination showed that the exposed threaded portions of the broken rod end lacked the required corrosion-preventative compounds or paint. Additionally, while the radial play of the bearing was within limits, the metal-to-metal contact between the inner and outer bearing races indicated the component should have been replaced according to the maintenance manual. The investigation also noted that while the aircraft's records showed compliance with a manufacturer's service bulletin, the specific service history of the individual part could not be verified, and the inspection requirements of the bulletin were limited to only the exposed threads.