What happened
While taxiing between ramps at Victoria International Airport in British Columbia, a Schweizer 269B helicopter, registration C-FRHO, suffered a sudden loss of anti-torque control. The aircraft experienced an abrupt rightward yaw, prompting the pilot to rapidly lower the collective from a height of approximately 10 feet. The resulting hard landing caused a main-rotor blade to strike the upper surface of the tail boom and resulted in the failure of all skid gear attachment points. The pilot sustained no injuries.
The investigation
Investigators examined the anti-torque system and discovered that a bumper plug was missing from the recently installed tail-rotor drive shaft. This component is critical because it rests internally within the drive shaft end couplings to restrict aft movement and prevent the splined drive from disengaging from the transmission input gear.
The aircraft had recently undergone assembly and maintenance involving multiple facilities. The initial assembly was performed by a contracted engineer at Starwest Aviation, an organization that lacked the necessary helicopter maintenance rating. This engineer, who was unfamiliar with this specific helicopter model, provided documentation claiming the drive shaft had been inspected, though the bumper plug was not detected.
Subsequent work was completed by A&L Helicopter Maintenance in Abbots-ford, which signed off on the airworthiness of the aircraft. However, the maintenance logs provided by this facility were found to be incomplete and lacked specific details regarding component exchanges or the extent of the work performed. While the maintenance manual requires specific checks for drive shaft end play and backlash, investigators found that the missing plug was not identified during the 25-hour, 50-hour, or 100-hour inspections that preceded the 200-hour service.
Findings
- The primary cause of the loss of yaw control was the disengagement of the tail-rotor drive shaft from the transmission input gear.
- This disengagement occurred because the bumper plug was missing from the aft end of the drive shaft.
- The missing component was not identified during maintenance because the engineer likely failed to consult the appropriate manuals and did not perform the required inspections correctly.
- The pilot was operating the aircraft solo and unsupervised without a helicopter endorsement.
- The initial assembly work was conducted by an engineer unfamiliar with the aircraft type under the direction of a maintenance organization not approved for helicopter work.