Accident Summary
After completing a swath run, the pilot pulled up and turned, then started a descent for another pass. As power was increased, the engine RPM rose from 3000 to 3100. Simultaneously, the pilot heard a whining noise and observed that the rotor RPM was decreasing. The pilot was unable to stop the descent before the helicopter struck the ground. After impact, the helicopter bounced and then rolled over.
Clutch Assembly Examination
Examination of the centrifugal clutch assembly (part number 47-620-609-1) revealed an estimated 60% contact between the shoe linings and the drum face. A minimum of 85% contact was required. The clutch did not conform to the specified toe-in requirements, and none of the heels of the clutch shoes were making contact with the drum.
Maintenance History
The helicopter had flown 220 hours since the last annual inspection, during which the clutch shoes were deglazed and the clutch drum was checked. It had flown approximately 13 hours since the last 100-hour inspection.