What happened
During a vertical reference operation on a steep mountainside, a McDonnell-Douglas 369 helicopter was transporting a driller's helper to facilitate hose connections. At approximately 1630 MDT, while climbing out after the first connection, the pilot experienced a sudden loss of cyclic control responsiveness. The pilot attempted an emergency landing on a steep talus slope, but the main rotor blades struck the hillside, causing the tail boom to sever.
The aircraft rolled onto its side and slid down the slope, causing the cabin roof and transmission cowl to tear away. The passenger, who was not wearing a lap belt, was ejected from the aircraft onto the rocks. The pilot, wearing a helmet, sustained serious head injuries as his head was dragged against the terrain during the slide. Both occupants were eventually evacuated by aircraft to hospitals for medical treatment.
The investigation
Investigators examined the engine, an Allison 2/250 C20B, and discovered the compressor was contaminated with bentonite, a type of drilling mud. While this contamination was present in the compressor and combustion chamber, it was not expected to cause a flame-out. The investigation also noted that the pilot had not activated the engine anti-ice system, which is required by the flight manual when operating in temperatures below 5 degrees Celsius with visible moisture.
Weather conditions at the time of the accident included overcast skies, light snow, and a temperature of approximately minus three degrees Celsius. The investigation focused on the cause of the sudden engine power loss during the climb.
Findings
- The helicopter experienced a sudden engine flame-out during the climb-out phase.
- The loss of power was likely caused by the sudden dislodging of snow accumulation within the air intake plenum.
- The aircraft was not equipped with an optional engine air inlet deflector kit, which is known to prevent snow ingestion in this model.
- The passenger's injuries could have been mitigated had they been wearing the required lap belt.
- The pilot's helmet played a critical role in reducing the severity of his head injuries.
Safety action
Following the investigation, the TSB issued an Aviation Safety Advisory to Transport Canada. The advisory recommended a review of the flight requirements for the MD 369 series when operating in falling or blowing snow, specifically assessing whether a requirement for an air deflector kit should be implemented.