Batesburg, SC, USA
N6020M
STINSON 108
Shortly after takeoff the engine sustained a total loss of engine power caused by fatigue failure of the crankshaft gear, necessitating the pilot to perform an off-airport forced landing that resulted in substantial damage. The fatigue fracture initiated from multiple origins at a corner of a keyway cut in the gear. The crankshaft gear underwent magnaflux inspection and was approved for return to service associated with an engine overhaul nearly 8 years and 247 hours earlier. While there was no evidence of plating at the fatigue initiation site, it could not be determined from the available evidence whether the fatigue existed in the part at the last inspection or how fast the fatigue crack was growing.
On July 23, 2022, about 1400 eastern daylight time, a Stinson 108-3, N6020M, was substantially damaged when it was involved in an accident near Batesburg, South Carolina. The private pilot and a passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that during cruise flight, while flying about 2,300 ft above mean sea level, the engine “went dead.” He made a forced landing to a field, and after touchdown the airplane collided with trees that bordered the field. Postaccident examination of the engine following recovery of the airplane revealed no valvetrain continuity with rotation of the crankshaft. Partial disassembly of the engine revealed that the crankshaft gear was fractured. Examination of the crankshaft gear by the National Transportation Safety Board Materials Laboratory revealed it failed due to fatigue that initiated from multiple origins at a corner of a keyway cut in the gear. There was no plating at the fatigue initiation site. A review of the maintenance records revealed a nearly 15-year gap in entries, and then the engine was overhauled by an airframe and powerplant mechanic on June 18, 2014, and installed on the airframe on June 1, 2016. Further review of the maintenance records associated with the engine overhaul revealed the crankshaft gear was magnafluxed and approved for return to service on April 25, 2012. Since installation, the engine remained installed in the airframe and underwent routine inspections and maintenance, accruing about 247 hours since major overhaul at the time of the accident.
The fatigue failure of the crankshaft gear, resulting in a total loss of engine power.
Source: NTSB Aviation Accident Database
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