Incident Overview
On January 13, 2012, about 1750 central standard time, a Cessna 150M airplane, registration N714BS, experienced a loss of engine power while cruising near El Dorado, Kansas. The private pilot, the sole occupant, was not injured. The airplane sustained substantial damage during the subsequent forced landing. The aircraft was registered to and operated by Prairie Air Service, Inc., of Benton, Kansas. Day visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under 14 Code of Federal Regulations Part 91. The flight had originated from Lloyd Stearman Field Airport (1K1) at 1700.
Flight Details
The pilot reported that he intended to assess the airplane's winter climbing capabilities before embarking on a long cross-country flight. He climbed to 10,700 feet but reported difficulty maintaining that altitude, necessitating a nose-high attitude. Deciding to descend, he reduced the throttle to the low end of the green rpm arc. Believing the engine rpm remained within the green arc, he did not engage carburetor heat.
After descending to 8,000 feet, the pilot applied engine power but could achieve only about 1,500 rpm. He then applied carburetor heat for over a minute and checked throttle and mixture controls, but the engine rpm continued to decrease. He established best glide speed and selected a highway for the forced landing. During the descent, the engine stopped windmilling. Shortly before touchdown, he noticed vehicles on the highway and, to avoid a collision, diverted to a triangular field. During landing, the nosewheel struck an embankment, causing the airplane to flip over and come to rest inverted.
Examination
A Federal Aviation Administration (FAA) inspector responded and reported substantial damage to the fuselage and vertical stabilizer. After recovery, an examination revealed the airplane was fueled with automobile gasoline (Mogas). Fuel was present in the gascolator, and the carburetor heat box controls operated freely. Spark plugs from each cylinder were removed and appeared fuel-soaked. The engine's magnetos produced spark when rotated by hand. No preimpact mechanical malfunctions or anomalies were found that would have precluded normal engine operation.
Review of the carburetor icing probability chart from FAA Special Airworthiness Information Bulletin CE-09-35 (dated June 30, 2009) and meteorological data indicated that conditions at several nearby airports were just outside those favorable for carburetor icing. The chart is based on aviation fuel, not Mogas. Additionally, air temperature and moisture content at altitudes of 8,000 to 12,000 feet were not conducive to carburetor icing. A review of Transport Canada's publication TP10737, "The Use of Automobile Gasoline (Mogas) in Aviation" (dated March 31, 1993), noted that Mogas is generally more volatile than Avgas, thus absorbing more heat from the mixing air during vaporization, which can result in ice accumulation at higher ambient temperatures and a higher likelihood of carburetor icing when flying on Mogas.
Conclusion
A reason for the loss of engine power was not determined.