WPR24LA240 · Cessna 182B

The pilot reported that after climbing to the airplane’s cruise altitude of about 9,000 ft mean sea level (msl), he configured the airplane to maintain straight and level flight and adjusted the mixture control to “rich of peak.” Shortly after leaning the fuel mixture, the engine began to run rough and a pronounced vibration began. The pilot made a 180° turn to the south, after which he observed a loss of oil pressure and the engine subsequently lost total power. During the forced landing, the airplane encountered a ditch and nosed over. Postaccident examination of the engine revealed about a 3-inch hole in the top of the crankcase above the No. 2 cylinder. Further examination revealed that the No. 1 piston had separated from the connecting rod wrist pin and fragments of the piston were present in the engine oil sump. The No. 2 piston connecting rod broke free from the crankshaft at the bearings, end cap, retention bolts, and nuts. Each of the cylinders and pistons displayed detonation signatures. There was no evidence of an induction leak on the No. 1 cylinder. While the pilot reported that his normal procedure was to operate the engine during cruise flight with a fuel to air mixture that was “rich of peak,” the procedure that the pilot described was more consistent with a lean mixture configuration as described by Section II in the cruise checklist of the manufacturer’s Pilot Operating Handbook. Given the pilot’s consistent and long-term operating procedure, it is likely that the fuel to air mixture was too lean and resulted in the explosive ignition of the fuel to air mixture within the No. 1 cylinder’s combustion chamber. The damage observed to the engine’s remaining pistons and cylinders was consistent with detonation signatures, resulting in a failure of the No. 1 piston and the No. 2 piston connecting rod, and the subsequent total loss of engine power.

Verbatim NTSB analysis and probable cause from the NTSB dataset