What happened
The aircraft was operating at a low altitude, approximately 80 to 100 feet above the ground. During this phase of flight, the pilot initiated a banked turn when the helicopter experienced an unexpected loss of power accompanied by significant vibration. In response to the mechanical failure, the pilot attempted to enter autorotation to maintain control and attempt a safe landing. However, during the descent, the aircraft struck a tree, resulting in substantial damage to the airframe.
The investigation
Following the accident, investigators examined the wreckage to determine the root cause of the power loss. The inspection focused on the transmission system, which is critical for transferring engine power to the rotor assembly. The examination revealed that the transmission clutch assembly shoes were worn and had separated from their mounting points. Additionally, the clutch drum was found to be extensively worn and scored, indicating significant mechanical degradation prior to the incident.
Findings
The primary factor contributing to the accident was the failure of the transmission clutch system. The separation of the clutch shoes and the condition of the clutch drum prevented the proper transfer of power, leading to the immediate loss of rotor drive. This mechanical failure occurred during a critical phase of flight at low altitude, leaving insufficient time or height for the pilot to recover safely without impacting an obstacle.
Safety message
Regular inspection and maintenance of transmission components are essential for helicopter safety. Wear on clutch assemblies can lead to catastrophic power loss if not identified and replaced during routine servicing. Operators must ensure that critical drive system parts are inspected according to manufacturer guidelines to prevent in-flight failures.