On May 23, 2012, about 1340 Pacific daylight time, a Cessna 150L, N11428, experienced a partial loss of engine power and nosed over during a forced landing to a field in Tulare, California. The student pilot, who was the registered owner, was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The student pilot and one passenger were not injured; the airplane sustained substantial damage. The local personal flight departed from Mefford Field Airport, Tulare, about 1300. Visual meteorological conditions prevailed, and no flight plan had been filed.
The student pilot stated that after departing from Tulare he was maneuvering the airplane in the local area. At an altitude about 1,300 feet above ground level (agl), the engine started to sputter and he configured the airplane for a forced landing in an alfalfa field below. During the landing rollout, the airplane encountered a water-filled ditch. The airplane nosed over inverted, sustaining damage to the tail section.
A review of the airplane’s logbooks revealed the airplane had undergone an annual inspection on October 12, 2011, at a total time of 3,238 hours. The student pilot had prior problems with the carburetor and thought that may have contributed to the sputtering engine. Following the accident, the airplane was sold to the student pilot’s past certified flight instructor (CFI). The CFI reported that he inspected the fuel tanks and found them clear and free of debris. The engine had no evidence of catastrophic mechanical malfunction or failure. The CFI removed the carburetor and did not find any anomalies that would have precluded normal operation.
A routine aviation weather report (METAR) generated by an Automated Surface Observation System (ASOS) at the Visalia Municipal Airport, Visalia, California (located about 10 nautical miles southwest from the accident site), indicated that about 5 minutes prior the accident the wind was variable from 320 to 020 degrees at 11 knots with wind gusts at 17 knots; temperature 79 degrees Fahrenheit; dew point 48 degrees Fahrenheit; and altimeter 29.89 inches of mercury.
The FAA published Special Airworthiness Information Bulletin (SAIB) CE-09-35 in June 2009, regarding carburetor ice prevention.
The SAIB noted that carburetor icing does not just occur in freezing conditions; it can occur at temperatures well above freezing temperatures when there is visible moisture or high humidity. Vaporization of fuel combined with the expansion of air as it flows through the carburetor (the venturi effect) causes sudden cooling. A significant amount of ice can build up within a fraction of a second. The SAIB contained a graph that illustrated the probability of carburetor icing for various temperatures, dew points, and relative humidity conditions. According to the SAIB, a pilot encountering the ambient conditions reported by the Visalia METAR could expect serious carburetor icing while at glide power.