WPR10LA248

During cruise flight, the pilot heard a loud “bang” and immediately observed oil coming from the engine cowling. The pilot subsequently initiated a forced landing and struck trees. A postaccident examination of the engine revealed two holes in the top of the crankcase between the Nos. 1 and 2 cylinders. The No. 2 connecting rod was visibly bent and no longer attached to the crankshaft. The end cap and a section of the yoke were separated and found outside of the engine case. The No. 2 cylinder piston, pin, connecting rod, and separated sections were sent to the National Transportation Safety Board’s materials laboratory for examination. A materials specialist determined that the damage to the connecting rod was a result of a high-cycle fatigue fracture. The fatigue in the location of the connecting rod would likely occur due to looseness in the connecting rod bearing area due to wear or damage to the bearing, small journal diameter, or insufficient clamping force from the connecting rod bolts. The bearing pieces did not show signs of significant wear and the journal diameter was not known. However, fretting was observed on the clamping surface of the connecting rod cap, which likely indicates that the connecting rod bolt had insufficient clamping force.

On May 18, 2010, about 1750 Pacific daylight time, a Cessna 210F, N580TP, lost engine power during cruise flight and made an emergency landing in an almond orchard near Arbuckle, California. The pilot/owner operated the airplane under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. The pilot, the sole occupant, received minor injuries. The airplane sustained substantial damage to the fuselage and wings. Visual meteorological conditions prevailed for the local area flight that departed the Colusa County Airport (O08), Colusa, California, about 1643. The flight was destined for Bob's Flying Service, Inc., Airport (32CL), Knights Landing, California, and no flight plan had been filed. The pilot reported that after two uneventful landings at O08 he departed south towards 32CL. About 25 minutes after he departed the airport, he heard a loud “BANG” and immediately observed oil coming from the engine cowling. The pilot further stated that, during this time, many alarm horns were going off in the cockpit. The pilot initiated a forced landing to an almond orchard; during the approach, the pilot kept the airplane above the tree tops until it stalled and impacted the terrain below. Post accident examination of the engine revealed two holes in the top of the crankcase between the number one and two cylinders. The number two connecting rod was visible through one of the holes and was bent. The connecting rod was still attached to the piston pin, but not attached to the crankshaft; the end cap and a section of the yoke were separated and found outside of the engine case. The crankshaft cheeks on either side of the number two connecting rod journal, and the aft counterweight assemblies, also had mechanical damage. All cylinders were borescoped; all contained light grey or normal deposits, and showed no signs of abnormal thermal discoloration. The number one and two cylinders were removed; both cylinders contained mechanical damage to the cylinder and piston skirts. The oil system was examined; the oil pump’s cavity and gear teeth contained scratches from hard particle passage. The oil sump was removed, and several dents were observed on the lower and aft sides. Sections of cylinder ring, piston material, two halves of a connecting rod bearing, and a connecting rod bolt and nut were found within the sump. Small pieces and particles of metal were also visible in both the oil filter and oil pickup screen. The number two cylinder, piston, pin, connecting rod, and separated sections were sent to the National Transportation Safety Board (NTSB) Materials Laboratory in Washington, D.C., for further inspection. The materials lab engineer noted that the connecting rod bolt had fractured in the threaded region. The fracture surface was smooth and curved slightly with no evidence of crack arrest marks, which are features consistent with overstress fractures. The connecting rod bolt cap had a matte gray rough appearance with somereduced area deformation adjacent to the fracture (necking), a feature that is consistent with an overstress fracture. According to the materials lab engineer, the fracture faces on each side of the saddle area of the connecting rod showed post-fracture contact damage. One of the fracture surface faces had relatively smooth fracture features with curving crack arrest lines that were consistent with high-cycle fatigue. The fatigue features emanated from an origin area in the vicinity of the cutout radius for the connecting rod bolt head. However, the fracture surface in the origin area had been obliterated by post-fracture damage. No evidence of ratchet marks was observed in the damaged area of origin. According to the aircraft maintenance logbooks, the engine was rebuilt and first installed onto the accident airplane in February 1993. Its most recent maintenance was an annual inspection, which occurred on February 26, 2010, at a tachometer time of 476 hours.