What happened
During a series of flight tests intended to adjust rotor blade alignment and autorotation RPM, an Eurocopter AS 350 BA, registration C-FPOO, experienced a critical flight control failure. The flight, operated by Héli-Inter Inc., included the pilot and two aircraft maintenance engineers (AMEs).
While performing a second autorotation at approximately 800 feet above ground level (agl), the collective lever locking plate accidentally engaged. This mechanism locked the flight control against the low stop, preventing the pilot from pulling the lever to arrest the aircraft's descent. Despite attempts to manually disengage the plate, the pilot could not free the control. The helicopter continued its descent and landed hard on Runway 36 at Val-d'Or. The impact caused the aircraft to bounce and land on its belly, severing the tail rotor drive shaft. The pilot escaped without injury, but the two AMEs sustained minor injuries, and the aircraft suffered substantial damage.
The investigation
The investigation examined the mechanical state of the aircraft and the maintenance history of the conversion from an AS 350 B to an AS 350 BA. Investigators found that several maintenance tasks related to the conversion had been left incomplete by the approved maintenance organisation. Specifically, the collective lever low-pitch stop adjusting screw had been left in an inverted position, and the connecting rods were shorter than manufacturer specifications.
Furthermore, the investigation scrutinized the oversight provided by Transport Canada. It was determined that the regulatory body had authorized the aircraft's conversion without adhering to the manufacturer's effectivity limitations and failed to detect significant deficiencies in the maintenance work performed during the rebuild process.
Findings
- The primary cause of the accident was the accidental engagement of the collective lever locking plate, which the pilot was unable to disengage in time to prevent a hard landing.
- Incomplete maintenance work, including an inverted stop screw and undersized connecting rods, allowed the collective control to overtravel downward. This overtravel reduced the clearance between the electrical console and the lever, facilitating the accidental engagement of the locking plate.
- The pilot's chosen procedure for checking rotor RPM—reducing engine power rather than maintaining full power as specified in the flight manual—increased the pilot's workload and complexity during the critical phase of flight.