Accident Overview
On July 30, 2019, at about 1630 central daylight time, a Piper PA28-140 airplane, registration N6754J, conducted a forced landing after departing the H L Sonny Callahan Airport (CQF) in Fairhope, Alabama. The flight instructor and student pilot were not injured, and the airplane sustained substantial damage. The airplane was registered to and operated by Lightning Aviation, LLC under 14 CFR Part 91 as an instructional flight.
Sequence of Events
The flight instructor reported that he was preparing the student pilot for a private pilot check ride. They had completed several touch-and-go landings. After the final landing, they planned to return to Foley Municipal Airport (5R4). Shortly after takeoff, the engine began to vibrate severely, then lost power. The instructor performed a forced landing in a cornfield about two miles from the airport.
Aircraft Examination
A Federal Aviation Administration inspector examined the airplane and found damage to the left wing and engine mount. Further examination of the engine's No. 3 cylinder revealed a failed exhaust valve. The No. 4 cylinder exhaust valve showed extensive erosion. The engine had accumulated 2,600 hours since its last overhaul; the manufacturer's recommended overhaul interval is 2,000 hours. The inspector noted that the flight school consistently operated engines beyond the recommended overhaul time.
Operational Context
The flight instructor reported that the leaning technique used while on the ground was to lean the mixture during taxi or engine idle. For the engine runup, they would set the mixture to full rich. During flight maneuvers at or below 3,000 ft mean sea level, they would not lean the mixture.
Figure 1 (referenced in the source) shows the failed exhaust valve.