What happened
During a training flight near Yellowknife Airport, Northwest Territories, a Eurocopter EC1obB helicopter, registration C-GRTA, experienced a sudden loss of engine power. The flight, which was intended for practicing emergency maneuvers, was conducting power-on approaches to a large clearing in the Twin Towers practice area. At approximately 1335 mountain standard time, while the pilot was increasing collective pitch during a final approach at roughly 150 feet above ground level, the rotor speed began to decay rapidly.
As the low rotor rpm warning horn sounded, the pilot also observed an engine oil pressure warning light. To avoid trees, the pilot attempted to stretch the glide into the clearing. This maneuver resulted in a high rate of descent and insufficient rotor rpm to cushion the impact. The aircraft struck the ground heavily, causing the main rotor blades to flex and the tail boom to sever. The two pilots on board sustained minor injuries, but the helicopter suffered substantial damage.
The investigation
Investigators examined the aircraft's systems and the engine at both the accident site and a maintenance facility. Testing of the Arrius 2F engine met all specifications and no anomalies were found that could explain the power loss. While the aircraft's engine monitoring display (VEMD) was partially recovered, the available data showed no instances of the engine operating beyond its normal limits.
Investigators also looked into the fuel system. Although the aircraft had been refueled with Jet A-1, the required fuel anti-ice additive was not used because it was unavailable at the airport. While no water or ice contamination was found in the fuel system during the wreckage examination, the absence of the additive was noted as a potential risk in the freezing temperatures present at the time of the accident.
Findings
- The helicopter experienced an engine power loss for undetermined reasons.
- The pilot did not identify the power loss until the rotor rpm had already decayed significantly.
- In an attempt to clear obstacles, the pilot stretched the autorotative glide, which further reduced the rotor rpm and led to the hard landing.
- The lack of fuel anti-ice additive created a potential risk for fuel system blockage, though it was not a confirmed cause of this specific event.