What happened
The incident occurred while the aircraft was engaged in a control burning operation. During this phase of flight, the pilot experienced a sudden and complete failure of the engine. In response to the loss of power, the pilot initiated an autorotation maneuver to maintain some degree of lift and control. However, the aircraft was unable to recover altitude or avoid obstacles, resulting in a collision with trees.
The investigation
Following the accident, investigators conducted a thorough examination of the failed engine components. The mechanical analysis focused on the point of failure within the engine assembly. Examination revealed that the number four connecting rod had fractured. Further metallurgical and structural analysis determined that the root cause of this fracture was fatigue cracking. This cracking had developed near the connection points between the crankshaft and the rod insert, eventually leading to catastrophic structural failure.
Findings
The investigation identified several key factors contributing to the accident sequence:
- The immediate trigger was a complete engine failure during critical flight operations.
- The mechanical root cause was fatigue cracking in the number four connecting rod near the crankshaft and insert connection.
- The pilot's response involved entering an autorotation, which is standard procedure for engine failure in rotary-wing aircraft.
- Despite the correct procedural response, the collision with trees could not be avoided due to the altitude and circumstances at the time of failure.
The combination of mechanical fatigue leading to sudden power loss during a control burnout resulted in the accident. The structural integrity of the connecting rod was compromised by fatigue, which is a progressive failure mode that can occur over time under cyclic loading.