NTSB Identification: LAX99LA287.
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Accident occurred Saturday, August 28, 1999 in EMIGRANT GAP, CA
Probable Cause Approval Date: 04/06/2001
Aircraft: Mooney M20J, registration: N4201S
Injuries: 2 Minor.

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 pilot was at cruise altitude of 9,500 feet when he heard a loud metallic bang. The airframe began to shake violently and the engine started running rough immediately following the noise. The pilot turned toward a nearby airport and the engine suddenly quit. The pilot was able to glide to the airport and touched down on the 3,300-foot-long runway; however, he had carried extra speed on the approach to allow a maneuvering margin to miss a large ravine off the runway's approach end. The airplane ran off the end of the runway and subsequently struck scrub bush. Postaccident examination of the engine revealed that the number three cylinder had separated in half between the Nos. 9 and 10 cooling fins. Metallurgical examination disclosed that the fracture was due to a fatigue crack, which had emanated from a notch and groove on the outer radius of one cooling fin. The notch and groove were painted the same color as the engine. The engine was overhauled 16 hours prior to the accident with 3 new cylinders installed, including the failed one.

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

The fatigue failure and separation of the number three cylinder due to the cylinder overhaul facility's improper inspection and quality control processes.

Full narrative available

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