Piper PA 25-235 N7336Z accident near Westphalia, Kansas

Probable cause

A total loss of engine power due to a fatigue failure of the crankshaft that resulted from main bearing shift and lack of lubrication.

NTSB analysis

The commercial pilot reported that he departed in the airplane with full fuel and chemical for the aerial application flight. After spraying a field for about 20 minutes, the engine experienced a total loss of power. The pilot jettisoned the chemical load and initiated a forced landing to a field. About 5 ft above the field, as the pilot tried to bleed off airspeed, the airplane stalled and impacted terrain.

Disassembly and examination of the engine revealed that the crankshaft was fractured, and the main bearings displayed thermal damage and smearing. Material examination of the crankshaft showed features consistent with a subsurface crack initiation and fatigue crack propagation. The fatigue striations, particularly near the initiation site, were consistent with high-cycle fatigue. The forward main bearings exhibited spalling, displacement, and cracking consistent with bearing wear fatigue. All the bearing damage was typical of similar bearings that had been operated at elevated temperatures using inadequate lubrication. The main bearing damage was likely the result of main bearing shift and a blockage of the lubrication paths. The blockage resulted in a lack of lubrication, main bearing failure, and a fatigue failure of the crankshaft. The reason for the main bearing shift could not be determined based on the available information.

Text from the NTSB. Open the NTSB docket for CEN17LA372 for the full record.