CHI99LA253

The pilot advised controllers that the aircraft engine was running rough and he was shutting it down. The pilot later stated that the engine began to shake violently and that he was concerned that the engine would become detached from the engine mount. The pilot executed a forced landing on a farm field. The aircraft had accumulated a total time of 62.5 hours and the new engine had accumulated 42 hours. External examination of the engine revealed three broken engine mounts. No other external evidence of damage was noted. The engine case was disassembled and the engine crankshaft was found to be broken at the connecting rod journal for the number one cylinder. A metallurgical analysis revealed striations typical of fatigue cracking. The fatigue origin was found to be 0.033 inches below the surface. No metallurgical anomalies were noted in a section made near the fracture origin.

On July 25, 1999, at 1046 central daylight time, a Beechcraft B36TC, N587DL, piloted by a commercial pilot, sustained substantial damage during a forced landing following an engine failure during cruise flight. The personal flight was conducted under the provisions of 14 CFR Part 91 and was operating on an instrument flight plan. Visual meteorological conditions prevailed at the time of the accident. The pilot reported no injuries to himself or to his one passenger. The flight originated from the Columbia Regional Airport, Columbia, Missouri, at 1017, and was enroute to Eppley Airfield, Omaha, Nebraska.

While in cruise flight at 10,000 feet altitude, the pilot advised air traffic control (atc) that he had an emergency. The pilot advised atc that the aircraft engine was running rough and he was shutting it down. The pilot was given vectors to the General John J. Pershing Memorial Airport (BZK), Brookfield, Missouri. The pilot executed a forced landing on a farm field approximately 5 miles south of BZK.

In a written statement, the pilot stated that the engine lost power while in cruise flight. The pilot stated that the engine began to shake violently and that he was concerned that the engine would become detached from the engine mount. He said that he reduced airspeed to 90 knots to maintain aircraft control. At this speed, the pilot felt that the engine would remain attached and he contacted Kansas City Center and advised them of his problem. The pilot selected a bean field in which to execute a forced landing. He said that while rolling out in the bean field, the "... nose wheel collapsed when we traversed a small swale in the bean field."

The aircraft was purchased new on February 22, 1999, and had accumulated a total of 62.5 hours of flight time prior to the accident. On May 14, 1999, the aircraft engine was replaced with a new engine in response to a Federal Aviation Administration Airworthiness Directive. The new engine had accumulated a total of 42 hours of flight time prior to the accident flight.

A postaccident examination of the aircraft was performed by the Federal Aviation Administration. No anomalies were found with respect to the aircraft structure, flight control systems, or other subsystems.

The engine was transported to the Teledyne Continental Motors facility in Mobile, Alabama, for a teardown inspection. External examination of the engine revealed three broken engine mounts. No other external evidence of damage was noted. Both magnetos were removed and tested and were found to operate. The vacuum pump and standby alternator shafts were sheared. The engine oil sump cover was removed and metallic debris was found covering the bottom of the cover. All of the cylinder overhead components were intact and no anomalies were noted. The piston and cylinder assemblies were removed and no anomalies were noted. The engine case was disassembled and the engine crankshaft was found to be broken at the connecting rod journal for the number one cylinder. No other anomalies were found with respect to the engine.

The engine crankshaft was examined in the National Transportation Safety Board's Materials Laboratory. The examination revealed the crankshaft chemistry was within specified manufacturing limits. Hardness testing of the nitride surface and of the core (zone below the nitride surface) indicated that the crankshaft was within manufacturing limits. The fracture revealed striations typical of fatigue cracking. The fatigue origin was found to be 0.033 inches below the surface. No metallurgical anomalies were noted in a section made near the fracture origin.

Parties to the investigation were the Federal Aviation Administration; Teledyne Continental Motors, Mobile, Alabama; Raytheon Aircraft Company, Wichita, Kansas; and Elliot Aviation, Omaha, Nebraska