Piper PA-18-150 N9764P accident near Canton, Georgia

Probable cause

A partial loss of engine power due to carburetor icing, which the pilot could not correct by applying carburetor heat because the movement of the carburetor heat control arm was restricted.

NTSB analysis

After performing maneuvers at 2,500 feet mean sea level (msl), the pilot was descending to 2,000 feet msl when the airplane’s airspeed and engine rpm began to decrease. The pilot checked the throttle position, mixture control position, fuel selector, and magneto selection, and cycled the carburetor heat, but was unable to regain full engine power. He landed the airplane in a nearby field, and during the landing roll, the airplane nosed over and came to rest inverted, resulting in substantial damage to rudder and vertical stabilizer. A postaccident examination revealed that a hole was worn in the lower section of the engine cowl and that the carburetor heat control arm did not have sufficient clearance from the lower engine cowl in that area. When the carburetor heat was activated, the carburetor heat control arm contacted and caught on the cowl, which limited the application of carburetor heat.

Thus, during the accident flight the lower engine cowl inhibited the movement of the carburetor heat control arm because of inadequate clearances. Because the temperature and dew point around the time of the accident were conducive to the formation of carburetor ice at cruise/glide power, it is likely that the engine lost partial power as a result of carburetor icing. The pilot was unable to apply full carburetor heat due to the limited movement of the carburetor heat control arm, and therefore was unable to regain full engine power.

Text from the NTSB. Open the NTSB docket for ERA13LA056 for the full record.