NTSB Identification: LAX02FA163.
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Accident occurred Monday, May 13, 2002 in GROVELAND, CA
Probable Cause Approval Date: 03/28/2006
Aircraft: Cessna T210M, registration: N761LX
Injuries: 2 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The airplane collided with multiple trees during an attempted forced landing in mountainous terrain following a catastrophic engine failure in cruise. The flight was obtaining VFR flight following from air route traffic control center (ARTCC) when the facility lost radar and radio contact. The airplane came to rest near the edge of an elliptical meadow, which was about 1 mile long by 1/4 mile wide, with the long axis oriented east and west. The meadow was in mountainous terrain and surrounded by trees over 100 feet tall. The debris path was along the eastern edge of the meadow on a magnetic bearing of 210 degrees. Multiple large trees were observed with broken branches and major impact marks on their trunks. The crankcase had a 3-inch diameter hole in it above cylinder number 3. Examination of the engine found that the crankshaft fractured and separated at the rear of the number 4 cheek. The fracture was at the forward radius of the number 2 main bearing journal. Smeared metal was on the fracture surfaces. A metallurgical examination determined that a large portion of the fracture surface exhibited smooth crack arrest markings typical of fatigue propagation. Failure of the crankshaft was caused by a fatigue crack in the cheek between the number 3 rod journal and the number 2 main bearing journal. The fracture of the crankshaft caused the additional damage to the engine, including the separation of the numbers 3 and 4 connecting rods from their respective journals, and would have led to a complete loss of engine power. The origin of the fatigue fracture was in the transition between the number 2 main bearing journal surface and the forward fillet radius, approximately 0.036 inches below the surface of the journal. No metallurgical anomalies or manufacturing process errors were found to explain the fatigue initiation. This failure is very similar to a number of others investigated by the Safety Board's Materials Laboratory in the past, with a fatigue crack initiating just below the hardened case layer. As with many of those previous events, there were no material or microstructural defects that could be identified as the root cause of the fatigue initiation. The crankshaft met design material specifications.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: a catastrophic engine failure due to the fatigue fracture and failure of the crankshaft. A factor contributing to the accident was the unsuitable nature of the mountainous terrain for a successful forced landing. The precipitating cause of the fatigue fracture could not be determined. Full narrative available
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