Background
The airplane departed with 24 gallons of usable fuel, which normally provides for 4.5 hours of flight. Two and a half hours into the flight, the engine began running rough.
Sequence of Events
The pilot confirmed that the mixture was set to rich and the carburetor heat was on. Approximately five minutes later, the engine stopped. The pilot executed a forced landing onto an area of tundra-covered terrain. The landing substantially damaged the undercarriage, fuselage, and left wing strut. About 30 minutes after landing, the pilot turned the fuel selector to the OFF position.
Postaccident Examination
A Federal Aviation Administration Inspector examined the aircraft after the accident. The carburetor had separated from the engine during the forced landing. The gascolator drain contained tundra material. Examination of the airframe and engine revealed no preimpact mechanical malfunctions or failures that would have precluded normal operation.
Guidance on Carburetor Icing
The carburetor icing chart indicated the possibility of serious carburetor icing under the reported atmospheric conditions. According to the Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A), the first indication of carburetor ice in an airplane with a fixed-pitch propeller is a decrease in engine rpm. The handbook states that when conditions are conductive to carburetor icing, carburetor heat should be applied immediately and should be left on until the pilot is certain all ice has been removed. Applying partial heat or leaving heat on for an insufficient time might aggravate the situation if ice is present.