Aircraft: Cessna 150. Injuries: 1 Serious. Location: Fitchburg, Mass. Aircraft damage: Substantial.
What reportedly happened: On the day of the accident, the student pilot, accompanied by a CFI, conducted a touch-and-go landing. While on the downwind leg of the traffic pattern for the second landing the engine began to run roughly.
The student applied carburetor heat and kept it on until touchdown. After landing the student disengaged carburetor heat.
During climb out after the second landing, the engine began running roughly again. The CFI took control of the airplane, lowered the angle-of-attack, and reapplied carburetor heat.
According to the CFI, the engine subsequently ran more roughly, so he immediately placed the carburetor heat to “off” but the engine still ran roughly.
The CFI decided that there was not sufficient remaining runway to land and he was not sure how much power the engine was producing or if he could maintain level flight. The CFI decided against attempting to turn back to the runway, so he continued straight ahead. The CFI then saw a building ahead and realized that the airplane was too low to fly over it, so he banked to the right to avoid it. The airplane mushed into trees.
A post-accident review of weather data and a carburetor icing probability chart revealed that, at the time of the accident, the ambient temperature and dew point favored serious icing.
Industry and FAA guidance advised pilots to be aware of the warning signs of carburetor ice, including loss of rpm and rough running engine and advised that the pilot should respond to these warning signs by immediately applying full carburetor heat, and that the engine may initially run roughly for a short time while the ice melts. Therefore, the flight instructor should not have turned off the carburetor heat when the engine was still running roughly after he turned it on.
Probable cause: A partial loss of engine power due to the formation of carburetor ice and the flight instructor’s improper application of carburetor heat.
NTSB Identification: ERA12FA143
This January 2012 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.