On July 30, 2019, about 1630 central daylight time, a Piper PA28-140 airplane, N6754J, conducted a forced landing after departing the H L Sonny Callahan Airport (CQF), 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 the provisions of Title 14 Code of Federal Regulations Part 91 as an instructional flight. The flight instructor reported that he was preparing the student pilot for his private pilot check ride and they had finished several touch-and-go landings. After the final landing, they planned to return to the Foley Municipal Airport (5R4). Shortly after take-off, the engine started a severe vibration, and then lost power. The instructor then preformed a forced landing in a cornfield, about two miles from the airport. An examination of the airplane by a Federal Aviation Administration inspector, found damage to the airplane's left wing and engine mount. Further examination of the engine's No. 3 cylinder revealed a failed exhaust valve. The examination also found extensive erosion on the No. 4 cylinder exhaust valve. He also noted that the engine had 2,600 hours since the last overhaul, adding that the engine manufacturer's recommended overhaul is 2,000 hours, and the flight school consistently ran the engines past the recommended overhaul time. Figure 1: Failed Exhaust valve FAA photo The flight instructor reported that the leaning technique used while on the ground, was to lean during taxi or engine idle. For the engine runup, they would go to a full rich mixture. He added that during flight maneuvers at or below 3,000 ft msl, they would not lean the mixture.