ANC25LA112

The total loss of engine power due to carburetor icing and the pilot’s failure to effectively use carburetor heat in meteorological conditions conducive to the formation of carburetor icing.

The pilot reported that, after encountering an unplanned headwind and deteriorating weather conditions with precipitation while enroute, he made the decision to divert to an alternate airport. While approaching his alternate airport, the airplane experienced a reduction in engine RPM, which resulted in a total loss of engine power. The pilot reported that he attempted to troubleshoot by checking that the fuel selector was on “both”, advancing the throttle and mixture to full, applying full carburetor heat; and confirming that the primer was secure; however, this did not result in the return of engine power. The pilot claimed that, at the time of the loss of engine power, both fuel tanks indicated about 8 gallons of fuel remaining. The pilot initiated a forced landing onto coastal sand dunes. The nose landing gear assembly sheared from the fuselage, and the airplane nosed over, which resulted in substantial damage to fuselage and wings. The pilot reported that the engine presented no indications of malfunctions or failures prior to the smooth and consistent lowering of the RPM over a 3 -4 second timespan; he stated that it sounded like the engine was running out of fuel. The pilot did not report any preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation and indicted that he was, “unsure of reasons for fuel or air starvation”. According to the Carburetor Icing Probability Chart (FAA SAIB CE-09-35), the atmospheric conditions at the time of the accident were conducive to serious carburetor icing at cruise power. The pilot stated, during a telephonic interview, that he had been operating the airplane with the carburetor heat control knob partially pulled to help regulate the engine’s cylinder temperatures. According to FAA Advisory Circular 20-113, “When [carburetor] icing conditions are present, it is wise to guard against a serious buildup before deicing capability is lost. The use of partial [carburetor] heat for ice prevention without some instrumentation to gauge its effect may be worse than none at all… The use of partial [carburetor] heat when the temperature is below 32° F may, for example, raise the mixture temperature up to the danger range, whereas, full carburetor heat would bring it well above any danger of icing.” Although the pilot reported that he applied full carburetor heat during the decline in engine RPM, it was likely insufficient to melt the ice. The pilot reported that the accident could have been prevented had he waited to conduct the flight until the weather had improved. According to FAA Advisory Circular 20-113, "To prevent accidents due to induction system icing, the pilot should regularly use [carburetor] heat under conditions known to be conducive to atmospheric icing and be alert at all times for indications of icing in the fuel system."