CHI07LA287

The airplane had just leveled off at 6500 feet, after departure, when the engine vibrated and lost full power. During an attempted return to the departure airport, the pilot realized that he could not make any runway and chose to make a forced landing into a corn field. The airplane was substantially damaged during the forced landing. Postaccident disassembly of the engine disclosed that the number two connecting rod had separated from the crankshaft; one of the connecting rod bolts had sheared. Inspection of the fracture surface of this connecting rod bolt disclosed there were signature marks of metal fatigue across the bolt shear face that had initiated at the surface of the bolt. The number two cylinder had been replaced about 8 hours prior to the accident; however, the connecting rod had not been removed from the crankshaft during the cylinder replacement.

On August 31, 2007, about 1645 central daylight time, a Mooney M20K, N231BQ, sustained substantial damage while making an emergency landing in a field near Fort Wayne, Indiana after experiencing a complete loss of engine power and severe vibrations. The personal flight was conducted under 14 CFR Part 91 flight rules. Daylight visual meteorological conditions prevailed at the time of the accident. No flight plan was filed. No injuries were sustained by the pilot or two passengers. The flight originated from DeKalb County Airport (KGWB) in Auburn, Indiana, and was destined for Indianapolis Metropolitan Airport (KUMP), in Indianapolis, Indiana.

After the accident, the engine was taken to Magnum Engines Inc., Fort Wayne, Indiana, where a complete disassembly of the engine was documented under the supervision of a Federal Aviation Administration (FAA) Principal Airworthiness Inspector from the South Bend, Indiana Flight Standards District Office. It was noted that a protruding hole was observed in the left and right crankcase halves above the number one and number two cylinder deck areas. An extensive amount of parts and metallic material were found in the oil sump. The oil filter exhibited light amounts of metallic particles after being cut open.

The number two cylinder connecting rod cap was separated from the upper portion of it's respective connecting rod. The number two connecting rod bearing exhibited mechanical damage with no signatures of lubrication distress or thermal distress. The upper yoke portion of the connecting rod separated from the base of the "I" beam. The number two connecting rod cap was flattened. The number one connecting rod was separated and found in the oil sump.

A bolt from the number two connecting rod was examined under an optical microscope at 20 power. The fracture surfaces exhibited signatures consistent with fatigue. The initiation point of the fatigue appeared to be at the surface of the bolt.

The aircraft's last annual inspection was conducted on April 9, 2007, at a tach reading of 602.0 hours. On August 2, 2007, at a tachometer reading of 634.7 hours (at an estimated engine total time since major overhaul of 906.1 hours), three cyclinders, the #1, #2, and #5 cylinders, were replaced with airworthy components. The oil and filter were also changed at that time. The engine was run up and leak checked OK. No visible metal was found in the old oil filter. Reportedly, the connecting rods were not removed from the crankshaft during the cylinder replacements.

The total airframe time at the time of the accident was 3,280 hours.