Cessna 150L N18690 accident near Matlock, Washington

Probable cause

A partial loss of engine power after a descent to a lower altitude due to the student pilot's delayed action in applying carburetor heat while operating in conditions conducive to carburetor icing.

NTSB analysis

The student pilot reported that while he was on his first solo cross country flight, the weather started to deteriorate. He descended to a lower altitude and as he proceeded towards the nearest airport, he noticed that the vertical speed indicator indicated a descent of 700 feet per minute. The pilot applied full power and the airplane continued to descend. The pilot elected to land on a nearby road. During the descent he ensured that the throttle was at full power, the mixture was full rich, and the fuel selector was on both fuel tanks. While on a base leg, the pilot applied carburetor heat. When he turned final he observed that he was too high; he idled the power and slipped the airplane to lose altitude. During the landing flare the left wing struck a sign; the airplane departed the roadway and came to rest inverted about 20 feet from the roadway. A postaccident examination and run of the engine revealed no mechanical failures or malfunctions that would have precluded normal operation. Weather at the time of the accident reported a temperature of 4 degrees C, and a dewpoint of 4 degrees C. When graphed on the Carburetor Icing Probability Chart provided by the Federal Aviation Administration, these weather conditions were conducive for serious icing at cruise power. It is likely that the pilot's delayed action in applying carburetor heat resulted in a partial loss of engine power due to carburetor icing.

Text from the NTSB. Open the NTSB docket for WPR13LA101 for the full record.