This November 2008 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Aircraft: Beech Bonanza. Injuries: None. Location: Bloomington, Ind. Aircraft damage: Substantial.
What reportedly happened: The pilot was flying on an IFR flight plan. The airplane was at 6,000 feet MSL when the engine began to run rough. The pilot advised air traffic control and attempted to divert to an airport about 10 miles to the west. Attempts to fix the rough running engine through troubleshooting were not successful. The pilot said the number one cylinder temperature had dropped and the engine oil pressure subsequently went to zero. He notified the controller that he would be unable to make it to the runway and set up for a forced landing in a pasture about 3.5 miles east of the airport. The terrain was hilly. After touchdown, the pilot was unable to stop the airplane before it went into a fence and trees.
The post-accident inspection revealed that the number one cylinder exhaust valve had failed at the base of the valve stem, damaging the intake valve and piston. The engine had accumulated about 1,130 hours since overhaul and the airplane had accumulated about 26 hours of flight time since the most recent annual inspection, which was completed approximately one month prior to the accident.
Probable cause: A partial loss of engine power due to a failure of the number one cylinder exhaust valve, and the associated secondary damage to the intake valve and piston.
For more information: NTSB.gov