Incident Overview
During an instructional flight, the right engine was shut down and its propeller feathered after a vibration was felt. The flight continued to its intended destination. Witnesses on the ground observed the right propeller rotating while the aircraft was on final approach, despite the crew having feathered it.
Propeller Failure During Ground Troubleshooting
After landing, the airplane owner, who held an A&P certificate, began troubleshooting the vibration issue. While the engine was running at 2000 RPM, one blade from the right propeller separated. The separated blade penetrated a hangar and the windshield of a parked airplane.
Examination Findings
A series of fatigue cracks was found on the propeller hub, located near the hub spider. The cracks originated at or near the hub surface. The propeller had been exposed to a ground strike 217 hours before the failure. Following the ground strike, the propeller was inspected and overhauled before being returned to service.