NTSB Identification: DEN00IA075.
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Incident occurred Tuesday, November 09, 1999 in BOULDER, CO
Probable Cause Approval Date: 04/06/2001
Aircraft: Beech A60, registration: N457DA
Injuries: 1 Uninjured.

NTSB investigators used data provided by various sources and may have traveled in support of this investigation to prepare this aircraft incident report.

The pilot said that as he descended to 6,500 feet mean sea level, the left engine of the twin-engine airplane failed. The pilot landed the airplane without further incident. The engine had 23.5 hours on it since major overhaul. An engine teardown revealed that the #6 connecting rod had failed. Examination of the #6 cylinder parts found preexisting fractures on both the rod cap and the connecting rod. The fatigue features displayed on the rod cap are suggestive of lower stress propagation than those stress propagation marks on the connecting rod. It appeared that the engine failure-initiating event was the failure of the rod cap. Examination of the #6 connecting rod bolts indicated that they fractured as a result of overstress.

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

The fatigue failure of the #6 cylinder connecting rod cap.

Full narrative available

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