NTSB Identification: FTW99LA025.
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Accident occurred Monday, July 27, 1998 in VERNON, TX
Probable Cause Approval Date: 08/03/1999
Aircraft: Mooney M20C, registration: N9744M
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.

The propeller blade separated during cruise flight and the aircraft started 'shaking violently.' The pilot pulled the mixture control to idle-cut-off and put the aircraft into a steep climb to stop the propeller. The pilot then diverted to an airport where he landed safely. The remainder of the blade was sent to the NTSB Materials Laboratory in Washington, D.C. A detailed examination of the fractured surface revealed crack arrest positions characteristic of fatigue cracking. Examination of the fatigue crack with a scanning electron microscope (SEM) revealed that corrosion pitting on the camber side of the blade was the origin of the fatigue crack. The propeller was last overhauled on November 16, 1989, and the last annual inspection was completed on January 1, 1998.

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

Fatigue cracking of the propeller blade which originated from corrosion pitting on its camber side, resulting in the blade tip separation during cruise flight.

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