The private pilot, who was also the builder of the experimental, amateur-built Sonex, reported that, during initial climb for the local flight, about 3,000 feet mean sea level, the propeller separated from the airplane and fell to the ground.
He turned the airplane toward an airport in Morganton, N.C., that had a longer runway than the departure airport and attempted to glide the airplane to the runway. However, the plane did not have sufficient altitude, and it subsequently hit trees about 600 feet short of the runway.
Photographs of the crankshaft revealed that it fractured just aft of the propeller mounting hub/flange. The fracture surfaces on the hub exhibited features consistent with fatigue crack propagation through the wall thickness of the crankshaft and the subsequent overstress fracture of the remaining portion of the crankshaft.
Review of maintenance records revealed that the airplane had sustained a propeller strike about seven years before the accident. After that, the owner, who performed his own maintenance, replaced the propeller, however, he did not disassemble the engine or otherwise document any inspection or replacement of the crankshaft in the airplane’s maintenance records.
Probable cause: The pilot/owner’s inadequate maintenance inspection following a propeller strike, which resulted in the subsequent in-flight propeller separation due to propagation of fatigue cracks in the crankshaft.
NTSB Identification: ERA16LA041
This November 2015 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.