Accident Overview
On September 28, 2017, at 1716 central daylight time, a Piper PA-25-235 airplane, registration N7336Z, impacted terrain following a loss of engine power while maneuvering at low altitude near Westphalia, Kansas. The commercial pilot, the sole occupant, was not injured. The airplane sustained substantial damage. The aircraft was registered to and operated by a private individual under 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The local flight departed Garnett Municipal Airport (K68), Garnett, Kansas, about 1630.
Pilot Report
According to the pilot, the airplane departed K68 with full fuel and chemical load. After spraying a field for about 20 minutes, the engine lost power. The pilot jettisoned the chemical load and initiated a forced landing to a field. When the airplane was about 5 feet above the field, the pilot attempted to bleed off airspeed, but the airplane stalled and impacted terrain. The left wing sustained substantial damage.
Engine Examination
The Lycoming O-540-B2B5 engine was removed from the airframe for further examination. Maintenance records showed the engine underwent a field major overhaul on January 28, 2016, about 218 hours prior to the accident.
On October 25, 2017, the engine was disassembled under Federal Aviation Administration supervision. Disassembly revealed a fractured crankshaft and main bearings with thermal damage and smearing. The crankshaft and main bearings were retained for further examination.
Materials Laboratory Findings
The fractured crankshaft and forward main journal bearings were examined by the National Transportation Safety Board Materials Laboratory. The crankshaft showed a fracture across a web between the second cylinder (C2) journal and the second main (M2) journal. Approximately 60% of the fracture surface had a flat portion with crack arrest marks emanating from near the corner of the web adjacent to the M2 journal. The crack arrest features were consistent with a subsurface crack initiation and fatigue crack propagation. Fatigue striations, particularly near the initiation site, were consistent with high-cycle fatigue.
The forward main bearing (M1) journal exhibited discoloration and dark circumferential wear marks on the aftmost two inches. One aft bearing surface showed spalling, displacement, and cracking consistent with bearing wear fatigue. The other aft bearing surface displayed spalling, material displacement, and smearing. Spalled and smeared material had accumulated in the lubrication groove. All bearing damage was typical of bearings that operated at elevated temperatures with inadequate lubrication.