Occurrence
On 12 December 2010, at approximately 0800 Central Standard Time, a Forest Helicopters Inc. Eurocopter AS 350 B2 helicopter (registration C–FORS, serial number 4001) was conducting slinging operations about 6 nautical miles northeast of the Pickle Lake Airport, Ontario. The pilot had picked up three fuel barrels with a longline and was transitioning into forward flight at low airspeed and about 250 feet above ground level when the engine lost power. The pilot jettisoned the load and attempted an autorotative landing. The helicopter struck the ground in a level attitude; one main rotor blade severed the tail boom. The pilot, wearing a 4‑point harness and helmet, was not injured and exited without assistance. The helicopter was substantially damaged; there was no post‑crash fire, and the emergency locator transmitter did not activate.
Flight History
The helicopter was supporting mining operations from a staging area. On the morning of the occurrence, the pilot removed winter covers and prepared the helicopter. Ambient temperature was −29°C; the fuel system had not been drained. After a normal start and warm‑up, the pilot conducted two flights to deliver drill crews, then returned to the staging area to pick up three fuel barrels. The barrels were placed in slings attached to a 100‑foot longline. The pilot began a vertical lift to clear 70‑foot trees and transitioned into forward flight. At about 40 knots and 250 feet AGL, the engine gas generator speed (Ng) and main rotor speed (Nr) gauges decreased rapidly. The pilot lowered the collective, applied forward cyclic, and released the slung load. The helicopter descended and struck the ground with forward momentum. The engine had stopped running before impact; total flight time was about 37 minutes. No abnormal indications were noted prior to power loss.
Investigation
Testing of the engine and fuel system could not identify a mechanical reason for the power loss. No blockage or contamination was found. The investigation determined that air could be introduced into the fuel system through a leaking FCU NTL or Ng drive fuel‑pump seal, routine maintenance, or draining fuel filters with boost pumps off. A leaking FCU NTL or Ng drive fuel‑pump seal had been identified during troubleshooting about 10 flight hours earlier, but the significance of this leakage in combination with boost pump check valves incorporating bleed ports was unknown at that time.
Findings as to Causes and Contributing Factors
The investigation found that:
- A leaking FCU NTL or Ng drive fuel‑pump seal, in combination with fuel boost pump check valves that incorporate bleed ports, likely allowed air to be introduced into the fuel system.
- The engine lost power, likely as a result of a flameout caused by an interruption in fuel flow due to entrapment of air in the fuel system.
- The engine power loss occurred at an altitude from which a safe landing was not assured.
Additional findings noted that draining the Le Bozec fuel filter with boost pumps off may introduce air into the fuel system, and that the Arriel 1D1 engine is not equipped with an auto‑ignition system, limiting relight opportunities after flameout.