Grumman American Avn. Corp. AA1B N8969L accident near Lititz, Pennsylvania

Probable cause

A partial loss of engine power for reasons that could not be determined because postaccident examination of the engine found no mechanical malfunctions or failures that would have precluded normal operation.

NTSB analysis

The flight instructor reported that he and a student pilot were performing touch-and-go landings in the airport traffic pattern at night; the instructor was flying the airplane. While on the downwind leg for the third and final landing, he reduced the engine power and the engine subsequently experienced a partial loss of power. The instructor switched the fuel tank selector and attempted to restore power, but was unsuccessful. He then performed a forced landing to a cornfield, during which the airplane nosed over. The instructor's statement did not address whether he used carburetor heat during the accident flight, and the carburetor heat control was found in the full-forward (off) position.

An examination of the wreckage revealed no evidence of preimpact mechanical anomalies with the airframe or engine. The spark plugs were light gray in color and exhibited normal wear. The fuel quantity onboard the airplane at the time of the accident could not be determined. Although the weather conditions at the time of the accident were conducive to the accumulation of carburetor icing at glide power, the reason for the loss of engine power could not be determined.

Text from the NTSB. Open the NTSB docket for ERA15LA276 for the full record.