Big Lake, AK, USA
N4380B
CESSNA 170B
During a landing to a remote off-airport gravel bar located along a river, while at about 20 ft above ground level, the airplane’s engine lost power. The engine then surged briefly before a total loss of engine power occurred. Subsequently, the airplane landed short of the gravel bar in the river and the airplane nosed over. The airplane sustained substantial damage to the left wing and empennage. A postaccident examination revealed no mechanical failures or malfunctions. A postaccident engine run was successfully performed. A non-aviation fuel tank was installed on the top of the fuselage to provide a fuel source. Air was applied to the fuel lines to provide pressure to ensure proper fuel flow, no contaminates were noted in the fuel lines. The temperature and dew point were entered into a carburetor icing probability chart, which coincided with the “serious icing in glide power” category.
On September 22, 2020, about 1900 Alaska daylight time, a Cessna 170B, N4380B, was substantially damaged when it was involved in an accident near Big Lake, Alaska. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 flight. According to the pilot, he was landing on a remote off-airport gravel bar located along a river. During short final, at about 20 ft above ground level, the airplane’s engine sputtered followed by a partial loss of power. The engine then surged briefly followed by a total loss of engine power as the propeller continued to windmill. Subsequently, the airplane touched down in the river short of the gravel bar and nosed over, coming to rest inverted in the river. The airplane sustained substantial damage to the left wing and empennage. The pilot reported that he had flown for about 1.5 hours prior to the accident and had about 1.7 hours of fuel remaining in the airplane’s fuel tanks at the time of the accident. He reported that he had been applying carburetor heat during his previous landings at the gravel bar and the fuel tank selector was set to BOTH during the approach. A Federal Aviation Administration (FAA) aviation safety inspector examined the airplane after recovery and did not observe any abnormalities. He stated that he drained the fuel from the gascolator and the fuel looked normal with no contamination present. A postaccident engine run was successfully performed. A non-aviation fuel tank was installed on the top of the fuselage to provide a fuel source. Air was applied to the fuel lines to provide pressure to ensure proper fuel flow, no contaminates were noted in the fuel lines. The weather observation station located about 25 nautical miles away from the accident site reported that, about the time of the accident, the temperature was 55.4° F and dew point 37.4° F. According to the carburetor icing-probability chart located in FAA Special Airworthiness Information Bulletin CE-09-35, the accident flight would have been operating in “serious icing in glide power”.
The pilot’s failure to utilize carburetor heat while flying in conditions conducive to carburetor icing, which resulted in a total loss of engine power.
Source: NTSB Aviation Accident Database
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