What happened
During cruise flight, the helicopter experienced a gradual loss of engine power. While the engine did not suffer a total loss of power, the partial power loss necessitated a forced landing.
The investigation
Examination of the wreckage identified that the throttle cable lower bellcrank arm had separated from the fuel control. Investigators found two brass bushings located at the throttle cable lower bellcrank arm assembly that were worn. Two steel bushings, which fit underneath the brass bushings at the lower bellcrank arm assembly, were also examined and found to be in an unworn condition.
Maintenance records indicated that the aircraft had undergone an annual inspection approximately five months before the accident. During that inspection, a mechanic noted two throttle cable bushings worn at the lower bellcrank arm; however, the part number recorded corresponded with the steel bushings rather than the brass ones. A company inspector evaluated this discrepancy and documented that the bushings were within limits, subsequently re-installing them. The records contained no mention of the brass bushings in the discrepancy list, the maintenance facility purchase order, or the customer invoice.
Since the annual inspection, the helicopter had accumulated approximately 75 hours of operation. This period included both a 25-hour and a 50-hour inspection. Additionally, the pilot performed multiple "First Flight of the Day" inspections following the annual inspection, which required checking the throttle linkage for freedom of movement and excessive play. None of these inspections detected the worn brass bushings.