Incident Overview
The pilot was performing an external load logging operation using a helicopter. After lifting two logs, a loud 'thunk' noise was heard. Subsequently, the helicopter experienced an uncontrolled turn to the right. The pilot found it impossible to lower the collective, which prevented maintaining adequate rotor RPM.
Examination Findings
Post-incident examination of the collective servo revealed internal leakage. This leakage caused a hydraulic lock within the servo, restricting its movement. Additionally, the servo's extension and retraction times exceeded the manufacturer's specifications.
Conclusion
The investigation determined that the collective servo had internal leakage resulting in a hydraulic lock, and its response times were outside specified limits.