Accident Overview
A single-engine airplane experienced a loss of engine power after encountering icing conditions while on an instrument cross-country flight at night. The aircraft was modified with a Soloy engine conversion, replacing the original 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.
Flight Sequence
The commercial pilot utilized the engine deice prior to encountering icing conditions. When the pilot perceived snow, he selected alternate engine air. Shortly after the alternate air was selected, the engine lost power. The pilot-rated passenger feathered and secured the engine before establishing best glide speed. The pilot attempted to restart the engine multiple times but could not obtain the 12 percent N1 required for start. As the airplane entered visual meteorological conditions, the pilot chose a gravel area for the forced landing.
Engine Examination
Post-accident examination revealed that the engine's anti-ice line had separated from the compressor case. Metallurgical analysis showed that the mounting pad separated from the compressor case due to fatigue cracking. The fatigue cracks 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 engine alternate air, relatively warm air was introduced into the engine inlet, dislodging accumulated ice and subsequently causing the engine to flame out.
Maintenance History
Maintenance records indicate that 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 a wait of up to 10 minutes before a successful restart.