What happened
During a normal cruise flight, the main rotor drive system failed for undetermined reasons. Following the loss of drive, the aircraft performed a touchdown. Upon landing, exhaust gases ignited the surrounding grass, resulting in a fire that completely destroyed the helicopter.
The investigation
An examination of the engine compartment was conducted, which revealed no evidence of catastrophic failure or malfunction within the transmission drive assembly. While the exact number of transmission drive belts in operation at the time of the failure could not be determined, the pilot noted that two belts are used to drive the transmission.
The pilot suggested that the loss of main rotor drive might have been caused by the stretching of either the transmission drive belts or the idler pulley cable. Records indicated that the tension of the idler pulley cable had been checked approximately 12 hours before the accident, and a recheck had been scheduled after 13 hours of operation.