NTSB Identification: CHI07LA038.
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Accident occurred Thursday, December 14, 2006 in Peoria, IL
Probable Cause Approval Date: 01/31/2008
Aircraft: Beech B36TC, registration: N30799
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The airplane experienced a loss of engine power and an in-flight fire during cruise flight, and was subsequently destroyed by fire after a forced landing in a field. The pilot reported that the airplane was in cruise flight when the engine started "missing." The pilot put the mixture to full rich, switched fuel tanks, and adjusted the propeller and throttle, but the engine continued to run rough. The pilot executed a forced landing in a field with the windshield 60 percent covered with oil and with smoke coming into the cockpit. The engine teardown inspection revealed that the #5 intake and exhaust valve heads were missing. The intake and exhaust valve stems and the exhaust valve guide were removed from the cylinder for further examination at the National Transportation Safety Board (NTSB) Materials Laboratory. The fracture surface of the exhaust valve stem (Part Number: SA643767P005 C FAA-PMA) was consistent with a brittle fracture mechanism such as fatigue. The maximum clearance of the exhaust valve guide (difference between the inner diameter of the valve guide and out diameter of the valve stem) was measured as 0.019 inch. According to the 1989 Teledyne Continental Motors (TCM) overhaul manual for the IO-520 engine, the maximum serviceable limit for exhaust valve guide clearance is 0.006 inch. Maintenance records indicated that an oil analysis taken on June 23, 2004, stated the following: "Note Extreme Nickel Concentration. High Concentration of Nickel is Caused By Valve Guide Wear. Contact Engine Manufacturer's Service Rep. Resample in 25 Hours." The aircraft owner reported that no maintenance was performed on the engine in regards to the oil analysis. The oil sample was taken at 663 hours since Time Since Overhaul (TSO). The engine failure occurred about 2.5 years later and had accumulated about an additional 300 hours of operation.

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

The loss of engine power due to a fatigue fracture of the exhaust valve as a result of maintenance not performed by the aircraft owner, and the unsuitable terrain encountered during the forced landing.

Full narrative available

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