Primary finding
Probable cause
The disruption of torque to the No 4 connecting rod journals, which resulted in a spun bearing and the subsequent total loss of engine power.
Investigator assessment
Analysis narrative
The pilots reported the airplane started to shake violently during cruise flight, and oil then covered the windscreen. The engine subsequently lost all power. The flight instructor took control of the airplane and performed a forced landing to a nearby airport. During the forced landing, the airplane’s main landing gear contacted the airport perimeter fence, resulting in the airplane nosing over. The airplane sustained substantial damage to both wings and the engine firewall. Postaccident examination of the engine revealed that the No. 4 cylinder crankshaft connecting rod journals showed evidence of lubrication distress and metal transfer between the bearing and the journal. Review of the airplane’s maintenance logbooks revealed that three of the engine’s six cylinders were replaced about 3 years before the accident, with the remaining three having been replaced about 2 years before the accident. Given this information, and the condition of the No. 4 connecting rod journals, it is likely that the torque on the journals was disrupted during the cylinder replacement(s) which resulted in a spun bearing.
Source record
Factual narrative
On January 21, 2024, about 1815 central standard time, a Cessna 210D, N3857Y, was substantially damaged when it was involved in accident near Paris, Tennessee. The flight instructor and pilot were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor was acting as the safety pilot for the pilot under instruction, who was working toward an instrument rating. While in cruise flight at 6,500 ft mean sea level, the pilot heard a “loud bang,” the airplane started to “shake violently,” and oil began to accumulate on the windscreen. The flight instructor took control of the airplane and diverted to Henry County Airport (PHT), Paris, Tennessee. The engine subsequently lost all power, and during the forced landing the airplane’s main landing gear contacted the airport perimeter fence. The airplane nosed over, which resulted in substantial damage to both wings and the engine firewall. Postaccident examination of the engine revealed a 5-inch diameter hole at the top of the crankcase between the Nos. 3 and 4 cylinders. Two quarts of oil were observed in the oil reservoir. Cylinder Nos. 5 and 6 were removed to gain better access to cylinder Nos. 3 and 4; damage to the cylinder skirts of cylinder Nos. 3 and 4 prevented their removal. The connecting rod remained installed to the piston pin and crankshaft in cylinder No. 3; however, the connecting rod for cylinder No. 4 was not present, and the connecting rod journal displayed thermal discoloration and metal transfer. Damage to the bottom of the piston was observed through the hole in the crankcase. The No. 4 connecting rod bolts and cap were recovered in two pieces from the oil sump along with multiple bearing remnants, pieces of the No. 4 piston and piston ring, and portions of both connecting rod bolts from the No. 4 connecting rod. Review of the airplane’s maintenance logbooks revealed that the last engine overhaul was completed 34 years before the accident on July 29,1990. Additionally, cylinder Nos. 1, 3, and 5 were replaced on May 1, 2021, and cylinder Nos. 2, 4, and 6 were replaced February 24, 2022.