Cessna 172 N4751F accident near Jamestown, New York

Probable cause

A partial loss of engine power for reasons that could not be definitively determined.

NTSB analysis

During a night cross-country instructional flight, the pilot receiving instruction performed a touch-and-go maneuver. Shortly afterward, during the climb to cruise flight on the return leg, the engine began to lose power. The flight instructor briefly attempted to troubleshoot the engine (including applying carburetor heat); however, he was unable to restore engine power, which remained at idle with the propeller windmilling. Because the airplane would be unable to reach an airport, the flight instructor established the airplane’s best glide speed. The airplane subsequently impacted trees.

Postaccident examination of the engine revealed that the single-drive dual magneto, which remained attached to the engine, would not produce a spark when the engine’s crankshaft was rotated. Internal examination revealed that, when the magneto’s input drive was rotated, neither set of contact points opened.

The magneto manufacturer’s service support manual stated that the magneto should be inspected every 500 hours with particular attention focused on rotating parts, bearings, and electrical components. The maintenance logbooks showed no record of 500-hour magneto inspections having been completed during the almost 2,000 hours that the airplane was operated since the operator had purchased it.

The weather conditions about the time of the accident were conducive to carburetor icing at cruise and glide engine power settings, and while the instructor applied carburetor heat with no engine power improvement after the engine had begun to faulter, it is possible that the engine might not have been developing sufficient heat by that point to deice an accumulation of ice in the carburetor. Thus, it could not be determined whether the anomalous operation of the magneto’s points that was observed during the postaccident examination, the possible formation of carburetor ice, or a combination of both these factors ultimately resulted in the partial loss of engine power during the accident flight.

Text from the NTSB. Open the NTSB docket for ERA22LA369 for the full record.