NTSB Identification: CHI03LA006.
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Accident occurred Monday, October 07, 2002 in Gregory, MI
Probable Cause Approval Date: 06/25/2003
Aircraft: Wolf Rotorway Exec-162F, registration: N1955Z
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

While in cruise flight, the secondary drive shaft failed completely and power to the main rotor was lost. The pilot executed an autorotation to an open field. However, on landing, the forward speed was higher than planned and the helicopter flipped forward and rolled to the left. The pilot stated that on his return to the airport, the secondary shaft bearing temperature started to rise. Once the bearing temperature reached 150 degrees Fahrenheit, the "drive let go", causing the engine RPM to surge. A post-accident inspection revealed that the secondary shaft had failed at a point inside the upper bearing race. Due to a history of failures of this secondary shaft design, Rotorway had released a 35 mm diameter shaft configuration in April 2001. The preceeding shaft diameter was 30 mm. An advisory bulletin was issued by Rotorway in May 2002. The 30 mm configuration was installed on the accident aircraft. In addition, the accident aircraft incorporated an after-market cog belt drive system between the secondary shaft and the main rotor shaft. The basic Rotorway design utilizes a chain drive system.

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

Failure of the secondary drive shaft, which resulted in a complete loss of power to the main rotor, and a high forward airspeed on touchdown, causing the helicopter to flip forward.

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