NTSB Identification: LAX00LA157.
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Accident occurred Sunday, April 16, 2000 in Yreka, CA
Probable Cause Approval Date: 04/17/2003
Aircraft: Cessna 207, registration: N1682U
Injuries: 2 Minor.
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 single engine airplane experienced a loss of engine power after encountering icing conditions while on an instrument cross-country flight at night. The accident airplane was modified with a Soloy engine conversion, which replaced the Continental TSIO-520 reciprocating engine with a Rolls Royce-Allison 250-C20S turbine engine. The engine was not equipped with an auto-ignition or continuous ignition system. The commercial pilot was utilizing the engine deice prior to encountering icing conditions, and selected alternate engine air once he perceived snow. The pilot reported that the engine lost power shortly after the engine alternate air was selected. The pilot-rated passenger feathered and secured the engine prior to establishing a best glide speed. The pilot attempted to restart the engine on numerous occasions; however, he was unable to obtain the 12 percent N1 required for engine start. As the airplane entered visual meteorological conditions, the pilot selected a gravel area for the forced landing. Examination of the engine revealed that the engine's anti-ice line was separated from the compressor case. Metallurgical examination of the anti-ice line revealed that its mounting pad separated from the compressor case as a result of fatigue cracking. The fatigue cracking originated from the braze joint, which displayed oxidation. According to the engine manufacturer and the engine conversion representative, the broken anti-ice line would have prevented heated air from entering the engine inlet guide vanes even with the engine deice selected. When the pilot selected the engine alternate air, relatively warm air was introduced into the engine inlet, dislodging any accumulated ice, and subsequently flaming out the engine. According to maintenance records, the engine underwent its last 100-hour inspection approximately 29 hours prior to the accident. A review of the engine operations manual revealed that due to thermal differences, the gas producing section of the engine may lock up after an in-flight engine shutdown, requiring the flight crew to wait up to 10 minutes before a successful restart.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the total loss of engine power while in cruise flight due to the fatigue failure of the engine's anti-ice bleed air line, which resulted in the pilot's inability to utilize the engine anti-ice system. Contributing factors were the icing conditions and the lack of suitable terrain for the forced landing. Full narrative available
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