On July 27, 2024, about 1157 Pacific daylight time, an Aeronca 11AC airplane, N86270, was substantially damaged when it was involved in an accident near Winchester, California. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot of the tailwheel-equipped airplane reported that he departed Brown Field Municipal Airport (SDM), San Diego, California, with an intended destination of Hemet Ryan Field (HMT) Hemet, California, a distance of about 70 nautical miles. About 6 miles from HMT, the engine rpm decreased from 2,400 to 2,000 rpm, which was followed by a vibration and grinding sound. The pilot applied carburetor heat and cycled between both magnetos, noting that the oil temperature remained within the normal operating range, but oil pressure was decreasing. The engine subsequently lost total power and the propeller remained windmilling. Following an unsuccessful attempt to restart the engine, the pilot initiated a forced landing to an open field. When the main wheels contacted terrain, the airplane nosed over and came to rest inverted. Postaccident examination of the airplane revealed that the left wing lift strut was bent and metallic debris was observed in the oil sump. The engine was disassembled by the former owner of the airplane. The crankshaft was found fractured in half at the forward side of the No. 1 cylinder connecting rod journal. The crankshaft was sent to the NTSB Materials Laboratory for further examination. Examination of the fracture surfaces revealed that the crankshaft fractured at the forward edge of the No. 1 connecting rod journal at the transition radius to the crankshaft cheek. The fracture surface was comparatively flat across almost the entire fracture and it exhibited beach marks, consistent with high-cycle fatigue over multiple duty cycles. The beach marks were traced back to an origin that was approximately 19° off bottom center of the journal. Supplied airframe and engine maintenance logbook excerpts showed that the engine was overhauled in April 1964, and at the time of the accident had accumulated about 1,569.4 hours. The supplied logbook excerpts consisted of 2 entries, and as such, it could not be determined what engine work was accomplished since the overhaul was performed. The engine manufacturer’s recommended time between overhauls is 12 years or 1,800 hours since overhaul.