What happened
While performing sling-load operations near the Haig Glacier in Alberta, a pilot was transporting equipment between a glacier, a camp, and a staging area. During the mission, the fuel low-level warning light illuminated, with the fuel gauge indicating 18 per cent remaining. The pilot continued operations, completing additional loads, but the gauge subsequently dropped to 11 per cent. While moving a net containing 900 pounds of empty propane bottles toward the staging area, the pilot noticed fluctuating fuel pressure and a further drop in the gauge to 3 per cent.
At an altitude of approximately 300 feet and an airspeed of 55 mph, the Turbomeca Arriel 1B engine flamed out. The pilot immediately released the sling load and attempted to increase speed to the recommended autorotative velocity of 70 mph. Aiming for a nearby highway, the pilot was unable to reach the target and instead flared the Aerospatiale AS 350B Ecureuil, registration C-GVMS, to land in a creek. The aircraft struck a steep creek bank at a high rate of descent, causing the tail boom to sever and the cabin floor to buckle. The pilot suffered two broken legs, seven fractured ribs, and several lacerations, and was trapped in the cockpit for approximately seven hours before being rescued.
The investigation
Investigators examined the fuel system and found that the fuel tank contained 11 litres of fuel at the time of recovery, which the flight manual defines as unusable. Testing of the fuel quantity transmitter revealed friction resistance in the float assembly, causing the gauge to provide inaccurate readings of up to six per cent. Specifically, the low-level warning light on C-GVMS activated when the tank still held 61 to 70 litres, even though the gauge indicated 18 per cent.
The investigation also looked into the aircraft's maintenance history and the pilot's experience. It was noted that the aircraft had not been updated with newer capacitor-type fuel gauging systems or modified tanks that reduce unusable fuel. Additionally, the NARCO 10 ELT failed to facilitate a rapid rescue due to a faulty transistor, which prevented the signal from being pinpointed by search satellites.
Findings
- The engine flamed out due to fuel exhaustion.
- The pilot chose to continue flight operations after the low-level fuel warning light had already illuminated.
- The pilot relied on the fuel quantity gauge rather than the warning light, a decision influenced by previous experience with different aircraft and recent maintenance reports suggesting the gauge was accurate.
- The fuel quantity gauge was reading up to six per cent higher than the actual fuel level.
- The aircraft was flying at a low altitude and 15 mph below the optimal autorotative speed at the moment of the flame-out, making a successful forced landing on the highway impossible.
- The malfunction of the ELT significantly delayed the rescue of the pilot.