Accident Overview
A helicopter experienced a loss of main rotor drive during normal cruise flight. The reason for the failure could not be determined. Upon landing, exhaust gases ignited grass, resulting in a fire that consumed the aircraft.
Examination Findings
Post-accident examination of the engine compartment revealed no evidence of a catastrophic failure or malfunction of the transmission drive assembly. The total number of transmission drive belts that were operating at the time of the failure could not be established.
Pilot Statement
The pilot reported that, in his belief, the loss of main rotor drive may have been due to stretching of the idler pulley cable or the transmission drive belts. He noted that two belts are sufficient to drive the transmission. The idler pulley cable tension had been checked approximately 12 flight hours before the accident and was scheduled for rechecking after 13 hours of operation.
Maintenance Records
According to available information, the idler pulley cable tension was inspected roughly 12 hours prior to the incident, with a planned re-inspection after 13 hours of flight time. The condition of the belts at the time of failure remains unknown.