NTSB Identification: FTW04IA134.
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Incident occurred Wednesday, May 19, 2004 in Kress, TX
Probable Cause Approval Date: 02/24/2005
Aircraft: Beech A23A, registration: N6943Q
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 1,911-hour certificated flight instructor reported that while in cruise flight, the propeller separated from the engine. The instructor stated that just prior to the propeller separating from the engine, he noticed a light oil spray covering the windscreen. The instructor then took control of the airplane and executed a forced landing to a nearby airport without further incident. The owner of the airplane reported that he was not aware of any anomalies leading to the failure of the propeller assembly, there were no pre-existing vibrations, no propeller changes, and to his knowledge, "no prior incursion or indications of this occurrence." Examination of the engine revealed that the crankshaft separated aft of the propeller flange. A metallurgical examination of the fractured area of the crankshaft revealed the fracture (consistent with fatigue) within the nitrided layer of the crankshaft originated from a small circumferential crack (consistent with overload) and progressed to the identification stamp. The origination from the original crack is undetermined.

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

The in-flight separation of the crankshaft for undetermined reasons.

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