On July 27, 1998, a Mooney M20C (registration N9744M) operated by Flight Training Center, Inc. was involved in an aviation accident near Vernon, TX. Investigators recorded the probable cause as: The propeller blade separated due to fatigue cracking initiated by corrosion pitting on the camber side of the blade. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 1 related events involving the same aircraft type or operator are linked below.
A propeller blade separated in cruise, causing violent shaking. The pilot stopped the propeller and landed safely. Examination revealed fatigue cracking originating from corrosion pitting.
Incident Description
During cruise flight, a propeller blade separated from the aircraft, resulting in violent shaking. The pilot responded by pulling the mixture control to idle-cut-off and initiating a steep climb to stop the propeller from windmilling. The pilot then diverted to an airport and performed a safe landing.
Examination Findings
The separated blade remnant was sent to the NTSB Materials Laboratory for detailed analysis. Examination of the fractured surface revealed crack arrest positions characteristic of fatigue cracking. Using a scanning electron microscope (SEM), investigators identified corrosion pitting on the camber side of the blade as the origin of the fatigue crack.
Maintenance History
The propeller was last overhauled on November 16, 1989, and the last annual inspection was completed on January 1, 1998.
Probable cause
The propeller blade separated due to fatigue cracking initiated by corrosion pitting on the camber side of the blade.