NTSB Identification: SEA02LA003.
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Accident occurred Friday, October 05, 2001 in Bend, OR
Probable Cause Approval Date: 02/20/2002
Aircraft: Ellsberg One Design, registration: N55TE
Injuries: 1 Minor.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
Just after the pilot entered the aerobatic box in his experimental One Design aircraft, the airplane developed an "extreme vibration." The pilot therefore shut the engine off and began a glide toward a nearby road. During the descent, with the propeller windmilling, the aircraft shook so violently that it was very difficult for the pilot to see, and he became concerned that the engine might separate from the airframe. When the aircraft reached the ground, the pilot tried to land on a narrow road, but with his visibility still significantly effected by the vibration of the airframe, he was unable to keep the One Design within the lateral confines of the road. During the landing roll, one of the main wheels departed the side of the road and encountered soft terrain. The main gear wheel then began to sink into the soft terrain, and the aircraft nosed over onto its back. It was later determined that one of the propeller counterweight mounting brackets (along with the counterweight itself) had separated from the propeller. A post-accident inspection of the counterweight on the apposing blade revealed that one of its mounting bolts was under-torqued approximately 115 inch-pounds below the value listed in the associated assembly torque table. The propeller, which was a non-certified model with composite blades, had been loaned to the pilot by the manufacturer, while his propeller was undergoing a periodic inspection.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the separation of a propeller counterweight mounting bracket due to incorrect mounting bolt torque. Factors include significant powerplant vibration during the forced landing, no suitable landing area, and soft terrain next to the narrow road on which the pilot attempted his emergency landing. Full narrative available
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