What happened
On a spring day in Manitoba, a Yukon Helicopters Ltd. Hughes 369HS was performing air taxi duties near St. Theresa Point. After picking up four passengers from the Waasag gomach Band Office, the pilot climbed to approximately 500 feet for a short flight back to the original destination. During the flight, observers noted unusual engine sounds and saw the aircraft lose speed and descend.
As the helicopter reached tree-top height over a frozen lake, the tail dropped and the aircraft tilted sharply to the left. The helicopter struck the ice on its left side, causing the main rotor blades to sever the tail boom and tail rotor assembly. The aircraft bounced, spun 180 degrees, and slid across the ice. The accident resulted in three fatalities and two serious injuries.
The investigation
Investigators examined the engine and fuel systems to determine the cause of the power loss. While the helicopter was operating without a fuel filter pressure differential switch, the fuel filter itself was found to be clean. The aircraft's weight and center of gravity were within permissible limits, and the pilot was fully qualified and not impaired by fatigue or drugs.
Technical analysis of the engine-driven fuel pump revealed that the No. 1 element was not pumping fuel. The investigation focused on the internal components of the pump, specifically the drive splines and check valves. The engine had experienced intermittent power fluctuations prior to the total failure, which were likely difficult for the pilot to diagnose in real-time.
Findings
- The engine suffered a complete loss of power due to the failure of the engine-driven fuel pump.
- The pump failure was caused by the progressive wear and failure of the drive splines within the pump's No. 1 element.
- This wear resulted from the use of incompatible components: a chromed drive shaft paired against non-chromed spur gear splines.
- The pilot lost control of the aircraft during an autorotation attempt because the rotor RPM decayed to a level that prevented effective control.
- The pilot's ability to manage the emergency was likely hindered by the difficulty of analyzing the initial power interruptions and the presence of a strong tailwind.