Accident Details
According to the pilot, the helicopter was on final approach at an altitude of 20 feet above ground level (AGL) and an airspeed of 40 knots when it 'abruptly yawed left.' Simultaneously, the engine RPM 'pegged off the dial.' The pilot responded by lowering the collective and rolling the throttle to idle. At approximately 5 feet AGL, the pilot increased the collective and applied 'slight' aft cyclic. The helicopter impacted the ground on the rear section of the right skid, bounced, and subsequently rolled over onto its left side.
Examination Findings
Examination of the helicopter at the accident site revealed that the clutch cable had separated. The clutch cable was examined and found to have failed as a result of high-cycle fatigue crack propagation on the individual wires. The initiation of the fatigue cracks correlated to an area of contact between the wires; however, there was no evidence of manufacturing or material defects in the cable assembly that could be associated with the failure. Examination of the failed cable also indicated that it may have been difficult to notice the failing clutch cable wires without disassembly.
Maintenance Considerations
According to the helicopter's maintenance manual, disassembly and inspection of the clutch cable and clutch assembly is to be completed every 400 hours. At the time of the accident, the helicopter had accumulated a total of 757.5 flight hours and 398.9 hours since the last 400-hour inspection.