Cessna 175 N7622M accident near Edgefield, South Carolina

Probable cause

The total loss of engine power due to a stuck engine exhaust valve. Contributing to the loss of engine power was the pilot’s failure to properly address the recurring stuck exhaust valve issue.

NTSB analysis

The airplane had not been flown for about 6 years before being purchased about a week before the accident. A stuck exhaust valve was noted as part of an inspection for purchase. The pilot, who was also an airframe and engine mechanic, performed an annual inspection on the airplane the day before the accident. The pilot did not use a checklist and relied on memory during the inspection. The pilot noted a stuck exhaust valve on the No. 2 cylinder. Instead of removing the cylinder and conducting an inspection, as suggested by the engine manufacturer, the pilot staked the valve to correct the condition. The valve stuck again during a predeparture check on the day of the accident. The pilot staked the valve again and performed several additional run-ups without noting anymore problems with the valve. An additional predeparture engine run-up was performed prior to the accident flight. The pilot departed and reported the engine began running rough after about 20 minutes of level flight. He turned toward a nearby airport but the engine subsequently lost all power. Attempts to restart the engine were unsuccessful so the pilot performed a forced landing to a field. The left wing struck a pole during landing as the pilot maneuvered to avoid livestock.

A postaccident engine run was conducted with the engine installed in the airplane. The engine run was limited to 1,500 rpm due to safety concerns. A noticeable “skip” was noted during the engine run. The engine subsequently ran rough and then lost power when the left magneto was selected but continued to run when the right magneto was selected. Timing of the left magneto could not be performed due to lack of available tools, and the reason the engine lost power when the left magneto was selected was not determined. Additional examination of the engine found that the exhaust valve guide of one cylinder was pulled from the cylinder and seized to the valve stem. Additionally, the pushrod socket of a second cylinder was separated, which also likely occurred because of a stuck valve. The accident would have likely been mitigated had the pilot/mechanic properly addressed the recurring sticking exhaust valve issue. Although the postaccident engine run noted an unidentified anomaly with the left magneto, the valve failures were likely the reason for the total loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA19LA143 for the full record.