While flying upslope with an external load of logs at almost zero airspeed, the pilot (PIC) heard an 'explosion' and noted that the helicopter pitched nose-up and rolled right. He turned to initiate a downslope forced landing, while experiencing control feedback and stiffness. As the crew began an approach, the copilot attempted to jettison the load with the electrical release; however, neither crew member verified the results of the procedure. As the aircraft continued to descend on the approach, the cargo hook struck the ground, opened, and released the logs. At the termination of the approach, the helicopter's main rotor blade struck several trees. After the helicopter touched down, it rolled onto its left side in a shallow stream. The No. 2 engine exhibited evidence indicating that it was producing power at impact; however, the No. 1 engine exhibited evidence indicating that it was not rotating. During subsequent inspections, no preimpact anomaly was found with either of the engines or of associated systems.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

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