Incident Overview
During level cruise flight, the propeller separated from the airplane. The pilot executed a forced landing at the Claremore Municipal Airport. On approach, the airplane porpoised, prompting the pilot to touch down in a grassy area between the runway and ramp. During the landing roll, the nose gear collapsed and the nose wheel separated from the aircraft.
Investigation Findings
Examination of the propeller attaching bolts showed they had failed in fatigue. The aft spinner bulkhead exhibited crescent-shaped arcs punched out, elongating its bolt holes. According to FAA service difficulty reports and reports from mechanics, there is a known potential for the aft spinner bulkhead to slide off the crankshaft flange bushings and rest on the propeller bolts during installation. In such a scenario, the mechanic would torque the propeller bolts with the aft spinner bulkhead pinched between the propeller spacer and the bushings. Over time, the pinched sections of the aft spinner bulkhead fail, leaving the propeller loose and ultimately leading to its separation.