On January 24, 2013, about 1545 Pacific standard time, a Cessna 150L, N18690, experienced a partial loss of engine power during cruise flight near Matlock, Washington. The pilot subsequently made an off airport forced landing onto a road. The student pilot was uninjured and the airplane sustained substantial damage to the right wing. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a solo cross country flight. Visual meteorological conditions prevailed and a visual flight rules flight plan had been filed, but was unopened for the flight destined for the Bremerton National Airport (PWT), Bremerton, Washington.
The student pilot reported that he was on the return leg of his first solo cross country flight. About 20 minutes into the flight, he was flying at an altitude of about 3,500 feet above ground level (agl) when the weather started to deteriorate. He descended to an altitude of about 2,500 feet agl and proceeded to the nearest airport that was reporting better weather. En route, he observed that the vertical speed indicator indicated a descent of 700 feet per minute. The pilot applied full power, but the airplane continued to descend; he elected to land onto a nearby road. During the descent he ensured that the mixture was full rich, the fuel selector was on both fuel tanks, and the throttle was at full power. The pilot made a left traffic pattern around the road and just before he turned base he turned on the carburetor heat. As he turned final he observed that the airplane was too high, he idled the throttle and initiated a slip to lose altitude. During the landing flare, the airplane struck a sign along the left side of the road, departed the roadway and came to rest inverted about 20 feet from the road surface. During the accident sequence, the left wing and empennage were substantially damaged.
A post-accident visual inspection of the engine revealed no visual anomalies. The cylinder rocker covers and spark plugs were removed; when compared to the Champion AV-27 chart, the spark plug electrode areas were consistent with 'normal' wear. The valves were undamaged and contained no abnormal thermal discoloration. Cylinder compression and valve continuity was obtained from all cylinders. The removed engine components were reinstalled and the engine was prepared for an engine test run. The airplane was started and idled temporarily before it was operated at various RPMs. There were no noted mechanical failures or malfunctions with the airplane's engine.
The nearest weather reporting station, Sanderson Field Airport in Shelton, Washington, was located at about 11 miles to the east of the accident scene. At 2353, weather was reported as few clouds at 1,700 feet agl, broken clouds at 4,200 feet agl, and overcast clouds at 5,500 feet agl, light rain, 10 miles of visibility, temperature 4 degrees C, dewpoint 4 degrees C, and an altimeter setting of 30.07 inches of mercury.
The temperature and dewpoint were graphed on the Carburetor Icing Probability Chart provided in the Federal Aviation Administration Special Airworthiness Carburetor Icing Prevention Information Bulletin and the conditions were conducive for serious icing at cruise power.