The pilot told investigators that he performed a preflight inspection of the Taylorcraft BC12-65 at the airport in Columbia, Tennessee, and confirmed there was about 12 gallons of fuel on board.
Including engine start, taxi, and pre-takeoff run-up operations, the engine was running for about 25 minutes with no anomalies noted.
Before takeoff he activated the carburetor heat and noticed a “normal” engine rpm drop. He also stated that he left the carburetor heat applied “for a little longer” and when he turned it off there was no engine rpm change.
He applied power for takeoff and the engine accelerated “strongly and smoothly.”
About 25 to 30 feet above the ground during the initial climb, the engine suddenly lost about 1,000 rpm.
The pilot elected to perform an off-field landing. He maneuvered to avoid a hedgerow and the airplane touched down in an area of high grass. During the landing the airplane was substantially damaged, while the pilot sustained minor injuries.
The wreckage was examined after recovery to a storage facility. The wing and main fuel tanks contained fuel and were uncompromised. Fuel drained from the tanks was clean and free of water or other contaminants. The carburetor bowl contained a small amount of particulate matter. The carburetor inlet screen was clear.
The engine was turned through manually by rotating the propeller. Compression and suction were noted on all four cylinders and valve action was correct. The magnetos produced spark to all leads when operated manually. The spark plugs were normal in color and wear when compared to a Champion inspection chart.
The carburetor was broken from the engine consistent with impact damage, however the cockpit controls remained attached. The carburetor heat knob was found in the “off” position.
Examination of the fuel system and engine did not reveal evidence of a pre-existing anomaly or failure that would have precluded normal operation.
The recorded temperature and dew point near the accident site was about 48° and 35°, respectively. On a carburetor icing probability chart, those temperatures were in the “serious icing — cruise power” range.
FAA Special Airworthiness Information Bulletin (CE-09-35) — Carburetor Icing Prevention, states that: “…pilots should be aware that carburetor icing doesn’t just occur in freezing conditions, it can occur at temperatures well above freezing temperatures when there is visible moisture or high humidity. Icing can occur in the carburetor at temperatures above freezing because vaporization of fuel, combined with the expansion of air as it flows through the carburetor (Venturi Effect) causes sudden cooling, sometimes by a significant amount within a fraction of a second. Carburetor ice can be detected by a drop in rpm in fixed pitch propeller airplanes and a drop in manifold pressure in constant speed propeller airplanes. In both types, usually there will be a roughness in engine operation.”
Probable Cause: A partial loss of engine power due to an accumulation of carburetor ice, resulting in an off-airport landing and substantial damage to the airplane.
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This November 2023 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
The STC for auto fuel allows 5% ethanol……
The Peterson and EAA STC for mogas specifies ‘NO ETHANOL’;
All Gasoline in California has ‘up to 10%’ ethanol, and now there is a proposal to allow 15% ethanol.
They do not mention whether the fuel was 100LL or Auto fuel?. Auto fuel contains 10 % ethanol and ethanol does attract moisture
The pilot mention there was no change in RPM, when he shut the carb heat?……..?
Continental engine carburetors hang down low under the engine and are more susceptible to carb icing……
It sounds like he had a carb ice build-up starting and the engine quit soon after take-off!
Don’t STCs for auto fuel prohibit ANY ethanol?
Mine did.
I burned 91 octane unleaded non ethanol. Unless they have a Rotax engine, or similar, it’s doubtful anyone is going to use ethanol gas in his airplane.
Carb temp gages were very common in the 40 and 50 year old planes. Sometime in the 60’s manufacturers decided to save money and no longer installed them. If you have a carbureted engine, you should have a carb temp gauge and know how to use it. Every year there is 5 to 10 accidents due to carb ice.
Too true —- always been a problem.
In his case, however, right at takeoff is unusual. The only way to catch that is to let the carb heat stay on after the drop on run-up and see whether it’s followed by a slow increase in rpm, of course. Naturally this is rarely done, or actively discouraged, because of the ingestion of unfiltered air into the engine for an extended period of time on the ground.
The best idea, as you say, is a carb temp gauge for those a/c types susceptible to it.