ATL94LA165

During cruise flight over mountainous tree covered terrain, the engine lost power. It continued to decrease to idle as the pilot glided the acft to a small clearing. The airplane was landed upslope, rolled over a hill, and could not be stopped before colliding with trees. There was no braking friction because of wet grass. During a post accident inspection, a stuck exhaust valve was found in the number 2 cylinder. The head of the valve stem was discolored and had the appearance of a varnish-like coating. Measurements of the valve stem and guide showed that the stem was 0.0075 micrometers larger than the guide. Fourteen months earlier a valve had stuck in the number 4 cylinder. Since the availability of the auto fuel STC, the engine had been operated about 25%-50% of its hours with auto fuel. Recent cylinder compression checks had been within limits.

On August 26, 1994, about 1900 eastern daylight time, a Cessna 150J, N50446, collided with trees during a forced landing roll near Spruce Pine, North Carolina. The airplane was operated by Eagle Wings Aviation under the provisions of 14 CFR Part 91, and visual flight rules. A flight plan was not filed for the local, surveillance flight. There were no injuries to the commercial pilot, nor the passenger, and the airplane was substantially damaged. Origination of the flight was the Avery County Airport, Spruce Pine, North Carolina, about 1730, on the same day.

The pilot reported that while returning to the airport, in cruise flight at 4,000 feet msl, the engine power reduced, followed by engine roughness, and the engine quit. Power continued to decrease, reaching idle power at touchdown. A landing site was selected in the densely wooded terrain and a forced landing was made. Wet grass reduced breaking friction and the airplane collided with a tree line, at the edge of the field, during the landing roll.

The number two cylinder exhaust valve was found stuck open, during the post accident inspection. A varnish-like discoloration was observed at the head of the valve stem. The valve guide was measured as 0.4315 micrometers, and the valve stem was measured as 0.439 micrometers. Previously, in June 1993, the number four cylinder had a stuck valve. Automotive fuel had been used in the airplane, in accordance with a supplemental type certificate (STC), between 25% and 50% of its operating hours, since the STC became available. Recent cylinder compression checks had been within limits.