On July 19, 2023, about 0615 central daylight time, an Pietenpol Aircamper airplane, N34KP, was substantially damaged when it was involved in an accident near Gardner, Kansas. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that shortly after takeoff, the engine started “missing” on one cylinder. The pilot reversed course back toward Gardner Municipal Airport (K34), Gardner, Kansas. The airplane was initially able to maintain altitude; however, as he approached the airport, the airplane began to descend. The engine ran rough and then lost all power. The pilot executed a forced landing to a construction site; the airplane nosed over and sustained substantial damage to both wings and the fuselage. A witness reported that he heard the airplane’s engine “cutting out” as the airplane descended to the field and then nosed over after landing. The airplane was equipped with an in-line, four-cylinder, liquid cooled Ford Model A engine with an owner-fabricated, electronic-type ignition system. A postaccident examination of the engine revealed that the No. 3 cylinder spark plug did not produce spark during field test with a Champion spark plug service unit cleaner and tester. Further examination revealed the No. 3 cylinder spark plug’s firing end contained hard cinder-like deposits, consistent with lead fouling when compared to the Champion Aviation Service Manual AV6-R. The spark plug functioned normally after its firing end was cleaned of the deposits. The other three spark plugs exhibited various degrees of lead deposits, but functioned when tested. The pilot reported that he used 100LL aviation fuel in the engine. Review of the engine logbooks revealed that the spark plugs were replaced during the last condition inspection and had accrued about 18.7 hours of service. There were no other preimpact mechanical malfunctions or failures with the engine or airframe that would have precluded normal operation.