NTSB Identification: DEN07LA083.
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Accident occurred Monday, April 09, 2007 in Topeka, KS
Probable Cause Approval Date: 09/27/2007
Aircraft: Beech 35, registration: N460B
Injuries: 1 Minor,1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
According to the pilot, shortly after departing runway 18 she heard what "sounded like a loud backfire, a single bang," and then the engine lost power. The pilot selected a nearby field and performed a forced landing. During the landing the nose gear collapsed resulting in substantial damage. An examination of the engine revealed that the crankshaft gear separated from the crankshaft and was loose inside the accessory case. The upper portions of five of the six screws used to secure the gear to the crankshaft were found in the accessory case. Metallurgical examination of the fracture surface revealed signatures consistent with fatigue fractures. One screw was sectioned and tested for hardness with the results of 29, 30, 30, and 31 Rockwell C Harness (HRC). According to TCM, the drawing specifies an H5 fastener with a hardness requirement of 32 through 37 HRC. In addition, the head of the screw had a diameter of .40 inches or less. The TCM drawing specifies a diameter of .44 inches. According to TCM, this could have resulted in inadequate torque for this installation. An examination of the airplane flight controls and engine controls revealed no anomalies.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The use of unapproved bolts to mount the crankshaft and gear together, causing fatigue and failure of those mounting bolts, resulting in the subsequent loss of engine power. Factors contributing to the accident were the separation of the crankshaft gear, and the lack of suitable terrain for a forced landing. Full narrative available
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