NTSB Identification: MIA04LA127.
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Accident occurred Sunday, September 05, 2004 in Brandon, MS
Probable Cause Approval Date: 09/13/2005
Aircraft: Mooney M20F, registration: N9708M
Injuries: 3 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 pilot stated that he performed a preflight inspection of the airplane and noted the oil capacity was full (8 quarts). Approximately 2 hours into the flight while flying at 10,500 feet, the engine began running rough. He advised air traffic control (ATC), and attempts to correct the rough running engine were unsuccessful. The flight continued and shortly afterwards, the engine developed a severe roughness and he then heard a bang with smoke entering the cockpit. He declared "mayday" with ATC, and requested vectors to the nearest airport. Unable to land there, he executed a forced landing on a nearby highway and collided with a vehicle during the landing roll-out. The No. 3 cylinder was found separated from the crankcase, and all cylinder studs and/or thru-bolts exhibited various forms of fatigue. The No. 3 cylinder connecting rod bolts which were fractured exhibited evidence of either bending or shear overstress. The No. 2 cylinder connecting rod bearing was found welded to the crankpin, and a piece of aluminum lined bearing material was found inside the oil passage of the No. 2 cylinder crankpin journal. Fretting was noted at the No. 3 cylinder contact area, and also at the split-line surface of the right crankcase half at the main bearing locations. The fretting was the greatest at the cylinder contact area between studs Nos. 1 and 2, and also at the split line surface on the right crankcase half at the No. 3 main bearing location. The engine had accumulated 1,390 hours since major overhaul and approximately 873 hours since the No. 3 cylinder was removed and reinstalled.

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

A loss of engine power due to the fatigue failure of all studs and/or thru-bolts of the No. 3 cylinder for undetermined reasons causing separation of the cylinder. Contributing to the accident was the unsuitable terrain encountered by the pilot.

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