What happened
The aircraft impacted vertically into a heavily wooded swamp. Evidence at the scene indicated that the impact occurred with a low rotor RPM and a high vertical rate of descent.
The investigation
Investigators determined that the belt drive clutch engagement cable had separated due to abrasion. This abrasion was caused by internal contact between the cable and various assembly components. This separation resulted in a mechanical disconnect between the engine and the transmission.
A review of maintenance records for the aircraft could not establish the exact total time elapsed on the cable. However, the records showed that the cable had been inspected and disassembled approximately 636.8 hours prior to the accident.
A manufacturer's service information notice had been issued regarding the cable assembly. This notice required an initial inspection within 50 hours of installation, followed by recurring inspections every 400 hours until the unit was replaced with an upgraded model. While the aircraft maintenance records did not show documented compliance with this specific information notice, the operator stated that the required inspections were being performed.