Engine Failure Leads to Controlled Crash in Mountainous Terrain (N8805W)

Accident Summary

While in cruise flight, the aircraft's engine began to lose power, and the pilot was unable to maintain the assigned altitude. The engine eventually quit, forcing the pilot to attempt a controlled crash in heavily forested mountainous terrain.

Post-Accident Findings

A post-accident inspection determined that the number four exhaust valve had stuck in the fully open position. There was a buildup of valve guide material on the valve stem. An examination of the aircraft logs revealed that the valve guides and stems had not been inspected in accordance with Lycoming Mandatory Service Bulletin 388C (which is not mandatory for aircraft operating under part 91) at the recommended 400-hour interval.

Pre-Accident Symptoms

It was also determined that the engine had been displaying symptoms typical of intermittent valve sticking—rough running for a few seconds immediately after start-up—prior to the accident flight and on a number of other prior flights. The pilot was unaware that the rough running was possibly associated with sticking valves and had not taken the aircraft to an Airframe and Powerplant mechanic to determine the reason for the symptom.