NTSB Identification: DEN00IA133.
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Incident occurred Saturday, July 01, 2000 in SPANISH FORK, UT
Probable Cause Approval Date: 04/19/2001
Aircraft: Diamond Aircraft Industries 20C-1, registration: N991CT
Injuries: 2 Uninjured.

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

The pilot had just departed on a cross-country flight, and had climbed to 9,500 feet. He said that he began to feel a 'heavy vibration' in the aircraft, and immediately turned towards the closest runway. Soon thereafter the propeller separated from the airplane, and the pilot performed a forced landing without further incident. Postincident examination of the maintenance records indicated that the attachment bolts for the wooden propeller were last torqued 110 hours before the incident. The manufacturer of the propeller recommends that their wooden propellers be torque checked every 50 hours of flight. Examination revealed that the propeller attachment bolts showed signs of fatigue failure. There was also fretting damage on the propeller extension flange and bushing shanks. The above-mentioned signatures are suggestive of the studs being insufficiently torqued by the mechanic during assembly or periodic maintenance procedures not being followed, and subsequently becoming loose during propeller operation.

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

The company maintenance personnel's inadequate torquing procedures of the propeller attachment bolts which resulted in the fatigue failure of the propeller attachment bolts and the in-flight separation of the propeller.

Full narrative available

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