Amateur-built SONEX N7035Z accident near Morganton, North Carolina

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 analysis

The private pilot, who was also the owner/builder of the experimental, amateur-built airplane, reported that, during initial climb for the local flight, about 3,000 ft mean sea level, the propeller separated from the airplane and fell to the ground. The pilot/owner turned the airplane toward an airport that had a longer runway than the departure airport and attempted to glide the airplane to the runway. However, the airplane did not have sufficient altitude, and it subsequently impacted trees about 600 ft 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 7 years before the accident. After that event, the pilot/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.

Text from the NTSB. Open the NTSB docket for ERA16LA041 for the full record.