What happened
At approximately 1000 EDT, an Expedition Helicopters Bell B206L helicopter, registration C-GSMZ, was performing a shallow climb toward a mineral exploration site north of Smooth Rock Falls, Ontario. During the ascent, the aircraft's Allison/Rolls-Royce 250-C20R engine suffered a sudden loss of power.
The pilot initiated an emergency autorotation over rugged terrain. In an attempt to reach a suitable landing area and avoid wooded areas, the pilot extended the glide. This maneuver resulted in a depletion of the main rotor RPM. Consequently, the aircraft performed a hard landing, which caused the tail boom to separate from the fuselage and the helicopter to roll onto its right side.
While the pilot sustained minor injuries, the two passengers escaped the aircraft without injury. A post-impact fire ignited by the engine bay destroyed the helicopter and spread to the surrounding area, causing a substantial forest fire.
The investigation
Investigators examined the engine at the TSB Engineering Laboratory. The teardown revealed significant internal damage, including fractured blades on the third- and fourth-stage compressor wheels. Specifically, at least 17 blades on the third-stage compressor wheel exhibited progressive cracks. The investigation determined that one of these cracks reached a critical size, causing the blade to fail under normal operating loads. The subsequent liberation of these blades caused overstress damage to the fourth-stage compressor wheel.
Findings
- The primary cause of the engine power loss was the failure of the third-stage compressor wheel due to progressive fatigue cracking.
- The loss of main rotor RPM during the extended glide prevented the pilot from arresting the aircraft's descent, leading to the hard landing.
- The engine's third-stage compressor blades had cracks that had propagated through approximately 50 per cent of the blade thickness.
Safety action
Following the investigation, the TSB released Aviation Safety Information Letter A06W0182-D1-L1, noting similar third-stage compressor blade failures in other recent occurrences involving the same engine model. In response, Transport Canada began drafting an Airworthiness Directive for Bell Helicopter Textron Canada (BHTC) model 206B series helicopters.