Accident Sequence
According to the pilot, the engine began to run rough while the airplane was in cruise flight at 6,000 feet mean sea level (msl). The takeoff and climb had been uneventful, and the instrument flight rules (IFR) flight had proceeded normally up to that point. The pilot advised air traffic control of the situation and decided to divert to an intermediate airport located approximately 10 miles west of his present position. In an attempt to address the rough running engine, the pilot increased the mixture, switched fuel tanks, and applied carburetor heat; however, these actions were not successful. The pilot noted that the #1 cylinder temperature had dropped and the engine oil pressure subsequently went to zero. He informed the controller that he would be unable to reach the runway and set up for a forced landing in a pasture about 3.5 miles east of the airport. The terrain in the area consisted of rolling hills. After touchdown, the pilot was unable to stop the airplane before it impacted a fence and trees.
Damage and Inspection
The airplane sustained substantial damage to the leading edges of both wings. A post-accident inspection revealed that the #1 cylinder exhaust valve had failed at the base of the valve stem. The intake valve and piston also sustained mechanical damage as a result of the exhaust valve failure. The secondary mechanical damage precluded a metallurgical examination of the fracture surface of the exhaust valve stem. The Continental E225-8 engine that powered the airplane had accumulated approximately 1,130 hours since overhaul. The airplane had accumulated about 26 hours of flight time since its most recent annual inspection, which was completed approximately one month prior to the accident.