What happened
During a cruise phase of flight, the aircraft was operating at an altitude between 150 and 200 feet above ground level (AGL). At this time, the surviving passenger reported hearing abnormal sounds emanating from the helicopter. Shortly after these noises were detected, the aircraft began to descend while banking to the right, ultimately impacting a wooded area.
The investigation
Following the accident, investigators conducted a thorough examination of the helicopter's mechanical components. The inspection focused on the flight control system to determine the root cause of the loss of control. The technical analysis revealed significant structural issues within the mixing unit assembly.
Specifically, the examination disclosed a fatigue failure of the lower mixing unit. Additionally, investigators identified a fatigue crack in the upper mixing unit. These defects were located on the flight control system, indicating that mechanical integrity had been compromised prior to the incident.
Findings
The primary finding centers on the structural failure of critical flight control components. The combination of the fatigue failure in the lower mixing unit and the crack in the upper mixing unit directly contributed to the aircraft's inability to maintain controlled flight. The abnormal sounds heard by the passenger were likely indicative of these progressive mechanical failures occurring just before the descent into the trees.