Accident
On May 18, 2010, at about 1750 Pacific daylight time, a Cessna 210F (registration N580TP) experienced a loss of engine power while in cruise flight. The pilot, who was the sole occupant and owner of the aircraft, performed an emergency landing in an almond orchard near Arbuckle, California. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed at the time of the accident.
Flight Details
The flight departed Colusa County Airport (O08) in Colusa, California, at about 1643, destined for Bob's Flying Service, Inc., Airport (32CL) in Knights Landing, California. No flight plan was filed. The pilot reported that after two uneventful landings at O08, he departed south toward 32CL. Approximately 25 minutes after departure, a loud "BANG" was heard, and oil was observed coming from the engine cowling. Multiple alarm horns sounded in the cockpit. The pilot initiated a forced landing to an almond orchard; during the approach, he kept the airplane above the tree tops until it stalled and impacted the terrain below.
Damage and Injuries
The pilot received minor injuries. The airplane sustained substantial damage to the fuselage and wings.
Post-Accident Engine Examination
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 remained attached to the piston pin but was separated from the crankshaft; the end cap and a section of the yoke were found outside the engine case. The crankshaft cheeks adjacent to the number two connecting rod journal and the aft counterweight assemblies also exhibited mechanical damage. All cylinders were borescoped and showed no abnormal thermal discoloration. The number one and two cylinders were removed; both contained mechanical damage to the cylinder and piston skirts.
Oil System and Debris
The oil system showed evidence of hard particle passage, with scratches on the oil pump cavity and gear teeth. The oil sump had several dents on the lower and aft sides. Within the sump were sections of cylinder ring, piston material, two halves of a connecting rod bearing, and a connecting rod bolt and nut. Small metal pieces and particles were found in both the oil filter and oil pickup screen.
Materials Laboratory Inspection
The number two cylinder, piston, pin, connecting rod, and separated sections were sent to the NTSB Materials Laboratory 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 crack arrest marks, consistent with overstress fractures. The connecting rod bolt cap displayed a matte gray rough appearance with necking adjacent to the fracture, also consistent with overstress fracture.
Examination of the fracture faces on each side of the saddle area of the connecting rod showed post-fracture contact damage. One fracture surface had relatively smooth features with curving crack arrest lines consistent with high-cycle fatigue, emanating from an origin area near the cutout radius for the connecting rod bolt head. However, the origin area had been obliterated by post-fracture damage; no ratchet marks were observed in the damaged origin area.
Maintenance History
According to the aircraft maintenance logbooks, the engine was rebuilt and first installed on the accident airplane in February 1993. The most recent maintenance was an annual inspection completed on February 26, 2010, at a tachometer time of 476 hours.