ZEIGLER, IL, USA
N9410U
CESSNA 150M
UPON COMPLETION OF A PRACTICE EMERGENCY LANDING PROCEDURE DURING AN INSTRUCTIONAL FLIGHT, THE ENGINE STARTED TO RUN ROUGH AND THEN QUIT. THE INSTRUCTOR WAS ABLE TO REGAIN PARTIAL POWER, AND MADE FORCED LANDING IN FRESHLY PLOWED FIELD. THE AIRCRAFT NOSED OVER JUST BEFORE IT CAME TO A COMPLETE STOP. THE ENGINE WAS TEST RUN ON THE AIRFRAME, AND RAN VERY ROUGH. DIFFERENTIAL COMPRESSION CHECK WAS PERFORMED WITH LOW COMPRESSION ON CYLINDERS #2 AND #4. FURTHER INVESTIGATION REVEALED THAT THE #2 AND #4 EXHAUST VALVES WERE BINDING WHEN THE VALVES WERE APPROXIMATELY 0.25 INCHES FROM THE SEAT. THE VALVE STEMS WERE EXAMINED AND FOUND TO HAVE A CARBON-LIKE DEPOSIT SURROUNDING THE STEM FROM THE VALVE FACE TO THE AREA ON THE STEM WHERE IT ENTERS THE VALVE GUIDE.
Source: NTSB Aviation Accident Database
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