On May 8, 1999, a Grumman American AA-5B (registration N4546J) was involved in an aviation accident near Claremore, OK. Investigators recorded the probable cause as: Fatigue failure of the propeller attaching bolts resulting from pinching of the aft spinner bulkhead during installation, causing it to fail over time and allow the propeller to become loose and separate. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A propeller separated from an aircraft in cruise flight, leading to a forced landing at Claremore Municipal Airport with nose gear collapse. Investigation found fatigue failure of propeller bolts due to potential installation issue.
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.
Probable cause
Fatigue failure of the propeller attaching bolts resulting from pinching of the aft spinner bulkhead during installation, causing it to fail over time and allow the propeller to become loose and separate.