Accident Overview
On April 11, 2019, at about 1608 Alaska daylight time, a Piper PA-32-300 airplane, registration N4466T, sustained substantial damage during an off-airport forced landing near Bethel, Alaska. The pilot and three passengers were not injured. The flight was operated as a Title 14 Code of Federal Regulations Part 135 domestic passenger flight from Aniak Airport (ANI) to Bethel Airport (BET).
Sequence of Events
According to the pilot, while en route, the engine began to sound “different,” and the oil pressure gauge indicated a loss of pressure below the green arc. Engine rpm decreased to about 2,000 rpm, and oil pressure continued to drop toward the yellow arc. The pilot turned toward Akiak Airport (AKI), the closest airport, and while adjusting propeller rpm, the engine lost all power. During the subsequent forced landing on a tundra-covered meadow, the main landing gear separated, resulting in substantial damage to the right wing.
Engine Examination
Post-accident examination revealed that the engine was seized and could not be rotated. The case halves were separated, exposing a failure of the crankshaft at the No. 3 main bearing journal. The failure exhibited thermal damage and twisting. The oil pan contained large amounts of copper and metal flakes, and the oil pan screen was heavily fragmented with metal shavings.
The fractured crankshaft and two halves of a bearing from main journal No. 3 were sent to the NTSB Materials Laboratory. Analysis showed crack arrest marks typical of fatigue cracking emanating from multiple origins near the center of the main journal. The fatigue origin area displayed blue, grey, and red tinting consistent with heat exposure. Post-fracture movement between mating surfaces obliterated some fracture features. The fatigue crack propagated toward the core, splitting into two cracks. The main journal surface had severe mechanical damage, including circumferential abrasion, wear, galling, heat tinting, and ladder cracking.
Maintenance History
The overhauled engine was installed in April 2019 and had accumulated about 14 hours of operation before the accident. The Lycoming Overhaul Manual for direct drive engines specifies magnetic particle inspection of the crankshaft. The work order for the engine overhaul indicated that magnaflux and zyglo inspections were completed, but these did not include the case or crankshaft. The repair station stated that non-destructive testing (NDT) parts are stamped “NDT” after inspection; the accident crankshaft had no visible NDT stamp.