Accident Overview
On April 3, 2014, about 1530 central daylight time, a Cessna T210L, registration N1631X, was substantially damaged during a forced landing to a road following a total loss of engine power near Clayton, Alabama. The flight instructor (CFI) was not injured, and the pilot receiving instruction received minor injuries. Visual meteorological conditions prevailed, and an instrument flight rules flight plan had been filed for the instructional flight conducted under Title 14 Code of Federal Regulations Part 91. The flight departed Valdosta Regional Airport (VLD), Valdosta, Georgia, about 80 minutes prior to the accident and was destined for Tuscaloosa Regional Airport (TCL), Tuscaloosa, Alabama.
Pilot Accounts
According to the CFI, after departing VLD and climbing to 6,000 feet above mean sea level, the engine fuel flow was lower than expected for the flight relative to the mixture control setting. The pilot receiving instruction added that about an hour into the flight, the engine "clunked and shuddered." The CFI assumed control, maneuvered toward a nearby airport, and the pilot receiving instruction initiated an unsuccessful engine restart. Both pilots reported engine oil pressure and propeller rpm indicating zero, and manifold pressure about 17 psi. After determining the airplane could not reach the airport, the CFI selected a grass field but switched to a road after discovering power line wires across the field. The pilot receiving instruction declared an emergency with Air Traffic Control just prior to the forced landing.
Aircraft and Damage
The airplane, manufactured in 1975, was registered to a corporation in 2004. It was equipped with a Continental Motors Inc. TSIO-520 series, 310 hp engine. Initial examination by a Federal Aviation Administration inspector revealed the engine firewall was crushed aft and both wings were substantially damaged.
Maintenance History
Maintenance logbook records showed a 100-hour inspection completed April 5, 2013, at a recorded tachometer reading of 8377.8 hours and engine total time of 892 hours. On January 10, 2014, the No. 2, No. 3, and No. 6 cylinders were removed, reworked, and replaced using torque values from the TSIO-550 Service Manual, which the engine manufacturer stated had the same torque values required for a TSIO-520 series engine. The log entry noted "leak checked and ground run satisfactory." On April 3, 2014, an oil change was performed: oil drained, new filter installed, 9 quarts added, and a ground run showed "ops normal, no leaks." There was no indication the oil filter was opened and examined as recommended in Advisory Circular 43.13-1B. The most recent oil filter dissection was on January 10, 2014, at the time of cylinder repair; no notation was made on the most recent inspection.
Engine Examination
On April 15, 2014, the engine was examined at a salvage facility in Griffin, Georgia, under NTSB supervision. The engine was intact with accessories attached. Spark plugs were light grey with normal wear per the Champion Check-a-plug chart. Magnetos operated and sparked on all towers. Crankshaft continuity could not be confirmed when rotated by propeller. The fuel pump tested normal. The oil sump contained metal particles. The engine case was separated; the crankshaft, two bearings, and connecting rods from cylinders No. 2 and No. 6 were sent to the NTSB Materials Laboratory. Torque values on crankcase through bolts were not obtained during disassembly. Continental Motors Service Bulletin (SB 96-7C) specified the "12 Point-Thru bolt at cylinder flange" should have a torque value between 790 to 810 inch-pounds.
Metallurgical Findings
The NTSB Materials Laboratory examination revealed the crankshaft fractured at the No. 2 main journal. The aft fracture surface was battered, obliterating most features; the forward face exhibited crack arrest marks. The adjacent journal showed circumferential wear scars and color changes (yellow, orange, purple, dark blue) moving aft to forward. The fracture surface exhibited fatigue striations consistent with fatigue crack propagation. Initiation sites were smooth with no material defects, inclusions, pits, or voids, and no machine marks in those areas. Along the bearing journal surface forward of the initiation sites were material deposits associated with galling wear, consistent with babbitt bearing material.
Similar Accident Reference
A review of a similar accident (ERA14LA193) revealed damage consistent with the circumstances and damage of this event. In that investigation, engine manufacturer personnel indicated that a crankshaft failure associated with a bearing shift usually fails in fatigue. Examination of that accident showed engine through bolts were not torqued to the required setting, resulting in a bearing shift, oil starvation, and fatigue crack failure in the crankshaft.