Event Description
During cruise flight, a helicopter experienced a gradual loss of engine power. The engine did not lose total power, but the partial power loss resulted in a forced landing.
Investigation Findings
Examination of the wreckage revealed that the throttle cable lower bellcrank arm had separated from the fuel control. Further examination showed that two brass bushings located at the throttle cable lower bellcrank arm assembly were found worn. Two steel bushings, which fit underneath the two brass bushings at the lower bellcrank arm assembly, were not worn.
Maintenance History
Review of maintenance records indicated that the helicopter underwent an annual inspection about five months prior to the accident. During that inspection, a mechanic noted two throttle cable bushings worn at the lower bellcrank arm. However, the mechanic referred to the part number corresponding with the two steel bushings. A company inspector evaluated the discrepancy and wrote that the bushings were found to be within limits and were re-installed. There was no mention of the brass bushings in the discrepancy list, the maintenance facility purchase order, or the customer invoice.
Subsequent Inspections
The helicopter had accumulated approximately 75 hours of operation since the annual inspection. A 25-hour inspection and a 50-hour inspection were performed between the annual inspection and the accident. Additionally, the pilot had performed multiple "First Flight of the Day" inspections subsequent to the annual inspection. That inspection required a check of the throttle linkage for excessive play and freedom. None of these inspections detected the worn brass bushings.