CEN23LA149

The pilot stated that, about 30 minutes after takeoff, he observed a subtle but abnormal engine vibration, and he began to return to the departure airport. The pilot reported that all engine indications were normal with the exception of one cylinder that displayed a high cylinder head temperature, but he could not recall which one. The engine subsequently lost total power, and the pilot performed a forced landing to a field, during which the airplane nosed over and incurred substantial damage. Examination of the engine revealed that the No. 6 connecting rod was separated from the crankshaft. Removal of the cylinders and pistons revealed damage due to detonation. Borescope examination revealed that the No. 5 piston was melted on the intake side and displayed evidence of severe detonation. Damage to the skirt of cylinder No. 6 prevented removal of the piston. All of the intake and exhaust valves and associated pushrods were intact with no damage noted, and there were no other anomalies detected during the engine examination. An interview of the mechanic who had performed recent maintenance revealed that all six cylinders were replaced with new or repaired units 90.7 flight hours beforethe accident. The mechanic stated that he had not performed a cold valve clearance check when the cylinders were installed. Since the engine could not be rotated, it was not possible to determine the valve clearance after the accident; however, it is unlikely that any valve clearance anomaly, if it had existed before the accident, would have resulted in the partial and then total loss of engine power. The vibration and high cylinder head temperature reported by the pilot are consistent with detonation, which likely led to the failure of the No. 6 connecting rod and a total loss of engine power; however, the reason for the detonation could not be determined based on the available information.

On April 7, 2023, about 1648 central daylight time, a Cessna 182Q airplane, N982NC, was substantially damaged when it was involved in an accident near Gardner, Kansas. 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 reported that the flight departed New Century AirCenter Airport (IXD), Olathe, Kansas, and was enroute to Lloyd Stearman Field Airport (1K1), Benton, Kansas. About 30 minutes into the flight, he noticed a subtle, abnormal vibration and elected to return to IXD. He stated that the engine gauges all indicated normally, and the only indication of an issue was the subtle vibration. As the airplane approached IXD, he noticed a high cylinder head temperature (CHT) on one cylinder, but he could not recall which cylinder. He adjusted the fuel mixture and was able to lower the CHT. As the airplane was descending, the engine went from full power to a partial loss of engine power and ultimately to total failure over a period of about 30 seconds. The pilot reported that, except for the one high CHT indication, all of the engine indications were normal until the engine lost power. During the subsequent forced landing, the airplane impacted a culvert and nosed over. The airplane sustained substantial damage to the fuselage. A postaccident examination revealed that the engine could not be rotated by hand. In addition, there was a hole in the top of the engine case above the No. 6 connecting rod, and the No. 6 connecting rod was separated from the crankshaft. Removal of the cylinders and pistons revealed varying damage consistent with detonation. The No. 5 piston was melted on the intake side and displayed evidence of severe detonation. Damage to the skirt of cylinder No. 6 prevented removal of the piston. All the intake and exhaust valves and associated pushrods were intact with no damage noted. An interview of the mechanic who had performed recent maintenance revealed that all six cylinders were recently replaced with new or repaired units 90.7 flight hours before the accident. All work was performed in accordance with the Continental Overhaul Manual. There was no mention of work performed on the pistons or rings being repaired. The mechanic stated in the interview that he had not performed a cold valve clearance check when the cylinders were installed.