What happened
On a flight near Matane, Quebec, a Bell 206B helicopter, registration C-GIFV, was conducting a low-altitude survey of the Saint Lawrence River's south shore to document damage from high tides. The aircraft, operated by Essor-Hélicoptères Inc., was carrying the pilot and four passengers at an altitude between 75 and 150 feet. Approximately 27 minutes after departing Matane, the Rolls-Royce 250-C20B engine suffered a sudden loss of power.
In response to the failure, the pilot initiated an autorotation that included a right turn exceeding 180 degrees. During the descent, the rotor RPM dropped below 90%, triggering the low RPM warning horn. The helicopter struck a beach with significant force, causing the landing gear to break and the aircraft to come to rest on its belly. The accident resulted in one serious injury and two minor injuries, while two occupants remained unharmed.
The investigation
The investigation focused on the mechanical failure of the engine and the circumstances of the landing. Investigators examined the engine's No. 2 bearing assembly and found that the cage had suffered a fatigue failure. This failure caused the compressor to shift forward, leading to contact between the impeller and the shroud, which induced friction, power loss, and a compressor stall.
While evidence of a broken gearbox stud and a cracked compressor scroll suggested abnormal vibrations, engine bench testing showed no anomalies. However, investigators noted that three fingers in the vibration damper had fractured within the 30 flight hours preceding the accident, potentially reducing the damper's effectiveness. Additionally, while the gearbox had been disassembled three times in the 35 hours prior to the crash, the ball bearings and vibration damper were not specifically inspected for wear during those maintenance events.
Findings
- The primary cause of the engine power loss was the fatigue failure of the No. 2 bearing assembly cage.
- A partial failure of the vibration damper may have increased the vibration load on the bearing assembly.
- The pilot's ability to execute a safe emergency landing was constrained by the low altitude and the need to perform a large turn into the wind.
- The rotor RPM dropped below the safe threshold because the collective was not fully lowered during the autorotation.
- The aircraft was operating at a weight that may have compromised its performance during the emergency maneuver.