Piper PA28 N6754J accident near Fairhope, Alabama

Probable cause

Failure of the No. 3 exhaust valve and the subsequent loss of engine power due to engine operation with an excessively lean fuel mixture over a period of time.

NTSB analysis

The flight instructor and student pilot had performed several touch-and-go landings; after the final landing, they departed for another airport. Shortly after takeoff, the engine started to vibrate severely and then lost power. The instructor performed a forced landing in a field, which resulted in substantial damage to the airplane's left wing.

Postaccident engine examination revealed a failed No. 3 cylinder exhaust valve and extensive erosion on the No. 4 cylinder exhaust valve. The engine had accumulated 2,600 hours since the last overhaul, which was 600 hours beyond the manufacturer's recommended time before overhaul.

The flight instructor reported that the leaning technique used while the airplane was on the ground was to lean the mixture during taxi or engine idle. For the engine run-up, they would use a full rich mixture. He added that during flight maneuvers at or below 3,000 ft mean sea level, they would not lean the mixture. However, the exhaust valve erosion is consistent with the engine being operated with an excessively lean fuel mixture over an extended period.

Text from the NTSB. Open the NTSB docket for CEN19LA265 for the full record.