On January 18, 2023, at 0903 eastern standard time, a Piper PA-31-350, N101MA, was substantially damaged when it was involved in an accident at Geauga County Airport (7GA), Middlefield, Ohio. The airline transport pilot and five passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 non-scheduled passenger flight. The purpose of the flight was to pick up a sixth passenger in Detroit, Michigan, before continuing to Minneapolis, Minnesota. As the airplane climbed through about 6,000 ft mean sea level (msl) in instrument meteorological conditions (IMC), the pilot observed oil leaking from the right engine nacelle. When the airplane reached about 7,400 ft msl, the pilot noted a loss of right engine power. He secured the engine, declared an emergency, requested to divert to the closest airport, and the air traffic controller vectored the airplane for the RNAV RWY 11 approach at 7GA. The pilot successfully completed the approach and reported that the airplane touched down in the “first one-third” of the landing runway at an airspeed “about 120 knots with zero flaps.” The pilot reported to a Federal Aviation Administration (FAA) inspector that he visually acquired the runway about 500 ft above the ground and knew he would not stop the airplane before it reached the departure end of the 3,500-ft-long runway, but chose to continue rather than abort the landing with one engine inoperative and climb the airplane back into IMC for another instrument approach. The airplane overran the departure end of the runway, continued through the grass overrun, and impacted a hill and a fence before coming to rest upright about 600 ft beyond the runway end. All three landing gear collapsed and the airplane sustained substantial damage to the wings and fuselage. According to FAA and maintenance records, the airplane was manufactured in 1977 and was powered by two Lycoming TIO-540-J2BD, 350-horsepower engines. The airplane’s most recent 100-hour inspection was completed on December 12, 2022, at 17,154.5 total aircraft hours, which was 42 hours before the accident. The right engine had accrued 1,662.5 total hours since major overhaul. Examination of photographs revealed substantial wrinkling of the fuselage and both wings as well as torn flight control surfaces. The right engine cowling was opened and examination revealed cracks in the engine crankcase. The engine was removed and examined at a local aircraft technician’s school. A large crack in the crankcase was visible above the No. 5 cylinder and the crankshaft nose seal was found partially displaced. Oil streaks originated from that point and covered the engine case. Oil streaking was also visible on the right engine cowling at the scene. Crankshaft rotation attempts were unsuccessful. Borescope examination of the No. 5 cylinder revealed damage consistent with detonation. The remaining cylinders did not appear to have the same extensive damage via the borescope. Attempts to remove the No. 5 cylinder were unsuccessful. Removal of the No. 3 cylinder showed minor detonation signatures in the combustion chamber and on the piston. The No. 5 cylinder was then removed, and the connecting rod was found broken at the large bearing end. Excessive heat and oil starvation signatures were observed at the connecting rod end. The partially-melted piston was removed from the No. 5 cylinder and a large crater was observed in the combustion chamber from the exhaust valve to the spark plug hole. Attempts to rotate the crankshaft with the two cylinders removed were unsuccessful, likely due oil starvation and heat damage to the crankshaft. The remaining rocker box covers were removed for visual examination with no discrepancies noted. The spark plugs displayed an “excessively rich mixture” coloration and were sent to Lycoming engines for analysis in their materials lab. The top spark plug from the No. 5 cylinder displayed a “badly damaged” insulator. When asked, the Lycoming engines representative said that detonation events are typically associated with a lean fuel mixture, and the damage displayed was the likely the result of detonation in the No. 5 cylinder. No source or anomaly that would result in engine detonation was identified. According to the Pilot’s Operating Handbook (POH) for the accident airplane, during a single-engine inoperative approach, the pilot should maintain an airspeed of 116 kts indicated (KIAS) or above until landing is assured. Once landing is assured, the pilot should extend the gear and flaps, slowly retard the power on the operative engine, and land normally. The airplane’s best single-engine rate of climb speed (blue line) was 106 KIAS, and its minimum controllable airspeed with one engine inoperative (Vmca) was 76 KIAS. The maximum speed for full flap extension (40°) was 132 KIAS. The POH also stated that a single-engine go-around should be avoided if at all possible.