What happened
On a daylight flight near Kapuskasing, Ontario, a Bell 206L helicopter, registration C-GDQH, was conducting a timber survey for a forestry client. The aircraft, operated by Sunrise Helicopters Inc., was flying at a low altitude and slow speed as part of its aerial survey mission. At approximately 10:48 EDT, the helicopter experienced an in-flight separation of one of its main rotor blades. This structural failure caused the aircraft to strike the terrain, resulting in 3 fatalities. The impact destroyed the helicopter and caused the engine and the main rotor system to separate from the fuselage during the descent.
The investigation
Investigators examined the wreckage and the components of the rotor system. While both blades remained attached to the hub, one blade had fractured, with an 8-foot section of the outboard end missing. The investigation focused on the manufacturing and maintenance history of the blades. The blades in question had accumulated 3592.1 hours of total time, approaching their 3600-hour design life.
Technical analysis of the fractured blade revealed that the failure originated in the leading edge spar. Investigators identified that micro-cracks in the adhesive material created a path for moisture to enter the blade's interior, leading to corrosion on the inner surface of the spar. This corrosion likely accelerated the fatigue process. Furthermore, the investigation looked into the maintenance practices of the operator, noting that several 'wipe checks' had been performed by personnel who were not licensed aircraft maintenance engineers, and some checks were conducted outside of the manufacturer's recommended intervals.
Findings
- The primary cause of the accident was the in-flight separation of the main rotor blade due to fatigue cracks originating from manufacturing defects.
- The damage tolerance inspection approach implemented after a previous 2008 accident was inadequate, as it failed to detect the progressing crack.
- Transport Canada's safety actions following the 2008 incident did not provide sufficient protection for this critical component.
- The risk of undetected defects was increased because maintenance tasks were performed by non-qualified personnel.
- Maintenance guidelines for inspection intervals were not strictly followed, increasing the likelihood of component failure.
- The risk of injury was increased because the passengers were not utilizing available shoulder harnesses.