On July 18, 2003, a Mooney M20F (registration N353JT) was involved in an aviation accident near Kerrville, TX. Investigators recorded the probable cause as: The loss of engine power due to the failure of the number three cylinder as the result of undertorqued cylinder bolts. A contributing factor was the lack of suitable terrain for the forced landing. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During cruise flight, a pilot shut down the engine after experiencing vibration, suspecting a runaway propeller. The forced landing resulted in collision with a fence and terrain. Investigation revealed the number three cylinder had separated from the 200 hp Lycoming engine due to fatigue cracking of crankcase bolts.
Incident Details
The pilot, who had accumulated 6,533 flight hours, reported that the engine developed a vibration while cruising. Suspecting a runaway propeller, the pilot elected to shut down the engine. During the subsequent forced landing, the airplane went through a fence and impacted terrain.
Engine Examination
Post-incident examination of the engine revealed that the number three cylinder had separated from the 200 horsepower Lycoming engine. Further investigation was conducted by the NTSB Materials Laboratory.
Metallurgical Findings
Metallurgical evaluation determined that the crankcase bolts were fractured due to stress fatigue cracking. The laboratory concluded that fatigue failure on cylinder mounting hardware is usually the result of insufficient torque loading.