Factual Summary
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 student pilot conducted an off-airport forced landing onto a road. The pilot was uninjured. The airplane sustained substantial damage to the right wing during the initial landing, and additional substantial damage to the left wing and empennage when it came to rest inverted about 20 feet from the road surface.
Details of Flight
The flight was the return leg of the pilot's first solo cross-country flight, operated under 14 CFR Part 91. A visual flight rules flight plan had been filed but was unopened. The destination was Bremerton National Airport (PWT), Bremerton, Washington. Visual meteorological conditions prevailed.
About 20 minutes into the flight, while at an altitude of approximately 3,500 feet above ground level (agl), the weather began to deteriorate. The pilot descended to about 2,500 feet agl and proceeded toward the nearest airport with better reported weather. En route, the vertical speed indicator showed a 700-foot-per-minute descent. Despite applying full power, the airplane continued to descend. The pilot selected a nearby road for landing.
During the descent, the pilot ensured the mixture was full rich, the fuel selector was on both tanks, and the throttle was at full power. He entered a left traffic pattern and activated the carburetor heat just before turning base. On final approach, the airplane appeared too high, so the pilot reduced throttle to idle 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.
Post-Accident Inspection
A visual inspection of the engine revealed no anomalies. Cylinder rocker covers and spark plugs were removed; spark plug electrode wear was consistent with normal operation per the Champion AV-27 chart. Valves were undamaged with no abnormal thermal discoloration. Cylinder compression and valve continuity were obtained from all cylinders. After reinstalling components, the engine was started and operated at various RPMs with no noted mechanical failures or malfunctions.
Weather Conditions
The nearest weather reporting station, Sanderson Field Airport in Shelton, Washington, about 11 miles east of the accident site, reported at 2353: few clouds at 1,700 feet agl, broken clouds at 4,200 feet agl, overcast at 5,500 feet agl, light rain, 10 miles visibility, temperature 4°C, dewpoint 4°C, altimeter 30.07 inches of mercury. When temperature and dewpoint were plotted on the FAA Carburetor Icing Probability Chart, conditions were conducive for serious icing at cruise power.