On attempting to start the engine for a post-maintenance ground run, the propeller turned through approximately three blades then stopped. Propeller was difficult to rotate forward or backward. Inspection of the starters Bendix drive shaft revealed cracks in the gear running parallel to the teeth, causing the gear not to properly mesh with the flywheel.
Multiple aircraft incidents involved failures of drive shafts or related components in critical systems, such as pressure pumps, turbochargers, alternators, and magnetos.
These failures led to the loss of essential aircraft functions, including instrument pressure, engine power, electrical supply, and engine starting capability.
Reported causes ranged from mechanical failures like shearing, breaking, and wear, to improper assembly or engagement of components such as set screws.
During a VFR instrument training flight, the instructor noted there was no instrument pressure from either engine. Inspection revealed both engine-driven pressure pumps had sheared their drive shafts. Technicians could not find any obvious reason for both shafts to fail.
Part total time: 88.6 hours
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