What happened
On a morning in Quebec, a private Enstrom F-28C helicopter, registered C-GVQQ, departed Mont-Laurier Airport for a local visual flight. The mission involved providing aerial footage of the area to two television news crews. During the flight, which was conducted at approximately 250 feet above ground level, the aircraft's engine experienced a sudden loss of power accompanied by backfiring.
As the pilot attempted an emergency landing, the aircraft struck cables spanning highway 117. The helicopter subsequently hit the highway and rolled into a ditch, where a post-impact fire completely destroyed the wreckage. The two fatalities included the pilot and a cameraman.
The investigation
Investigators examined the engine and the aircraft's maintenance history. They discovered that a fracture in the check ball retainer within the exhaust valve hydraulic tappet had caused the valve clearances to increase. This mechanical failure caused the valve to open late and close early, leading to the engine backfiring and losing power.
Regarding maintenance, the investigation found that while the engine had not reached its recommended airtime for overhaul, it had been in service for over 27 years since its last overhaul. The investigation also noted that the aircraft's journey log did not record all flying hours, and certain maintenance aspects deviated from established standards.
Furthermore, the investigation looked into the pilot's training and the flight conditions. At the time of the power loss, the pilot had very little time—approximately 15 seconds—to execute an emergency landing procedure. The investigation also noted that the pilot was managing significant workload fluctuations in rotor RPM and torque due to the engine's instability.
Findings
- A fractured check ball retainer in the hydraulic tappet caused the No. 4 cylinder exhaust valve to malfunction.
- This valve malfunction resulted in backfiring and a partial loss of engine power.
- The loss of power prevented the aircraft from maintaining its cruise altitude.
- During the emergency descent, a decrease in main rotor RPM led to a loss of directional control.
- The pilot's focus on the emergency maneuver likely prevented the detection of the cables spanning the road.