NTSB Identification: SEA02FA009.
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Accident occurred Sunday, November 04, 2001 in Miles City, MT
Probable Cause Approval Date: 10/24/2002
Aircraft: Cessna 175C, registration: N8347T
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

During en route cruise, the number four cylinder exhaust valve guide separated from its associated cylinder head. When the aircraft was approximately 12 miles from the airport, the head of the number four cylinder exhaust valve separated from the valve stem. The exhaust valve head then dropped into the number four cylinder where it repeatedly impacted the piston dome and the cylinder head ceiling. This was followed by approximately 30 percent of the piston dome failing inward, resulting in the pressurization of the crankcase through the open exhaust valve port. As a result of the pressurization of the case, one of the number six cylinder pushrod-to-crankcase seals was forced off of its crankcase mounting surface, allowing the majority of the oil to escape from the engine. Soon thereafter, due to thermal stress, the number one connecting rod separated from the crankshaft and punched holes in the crankcase near the number one and number two crankshaft journals. After experiencing a total loss of power, the pilot attempted to land on the uneven rolling terrain, but due to the darkness of the night collided with the terrain.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The separation of the number four cylinder exhaust valve guide from the cylinder head, leading to the failure of the exhaust valve stem and the catastrophic failure of the engine while in cruise flight. Factors include the necessity of attempting a forced landing in rolling/hilly terrain on a very dark night.

Full narrative available

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