Bethel, AK, USA
The pilot reported that, while in cruise flight, the engine lost partial power, then total power, and the propeller stopped turning. During the subsequent off-airport forced landing on the tundra meadow, the main landing gear separated from the airplane, resulting in substantial damage to the right wing. Examination of the engine revealed a crankshaft failure that was likely a result of fatigue cracking that emanated from the surface of the main journal. The engine was overhauled at a certified repair station about 14 flight hours before the accident. The engine manufacturer overhaul manual stated that the crankshaft was to be inspected using a magnetic particle inspection procedure as part of the overhaul; however, the crankshaft was not inspected as part of the overhaul. It is likely that if the crankshaft had been inspected as indicated, the fatigue cracking would have been detected and corrected during overhaul.
On April 11, 2019, about 1608 Alaska daylight time, a Piper PA-32-300 airplane, N4466T, sustained substantial damage when it was involved in an accident near Bethel, Alaska. The pilot and three passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 domestic passenger flight. The pilot reported that, while en route from Aniak Airport (ANI), Aniak, Alaska, to Bethel Airport (BET), Bethel, Alaska, the engine began to sound “different,” and he observed a loss of engine oil pressure below the green arc. The engine rpm decreased to about 2,000 rpm, and the oil pressure continued to decrease to the yellow arc. As he turned the airplane toward Akiak Airport (AKI), Akiak, Alaska, the closest airport, and while adjusting the propeller rpm, the engine lost all power. During the subsequent off-airport forced landing on the tundra-covered meadow, the main landing gear separated from the airplane, resulting in substantial damage to the right wing. Examination revealed that the engine was seized and could not be rotated. The case halves were separated, revealing a failure of the crankshaft on the No. 3 main bearing journal. The failure showed signs of thermal damage and twisting. The engine valves were all set correctly and properly installed. The oil pan contained large amounts of copper and metal flake. The oil pan screen was removed, and heavily fragmented metal shavings were found. The fractured crankshaft and two halves of a bearing from main journal No. 3 were sent to the NTSB Materials Laboratory. The examination revealed that crack arrest marks typical of fatigue cracking emanated from multiple origins at the surface of the main journal. The fatigue origin area was located near the center of the main journal. The fracture face at the fatigue origin area exhibited evidence of blue, grey, and red tinting consistent with heat exposure. The fracture features at the origin of the fatigue crack and other portions of the fracture were obliterated by post-fracture relative movement between mating fracture faces. The fatigue crack propagated toward the core of the main journal, where it split into two fatigue cracks. The surface of the main journal exhibited evidence of severe mechanical damage such as circumferential abrasion, wear, galling and heat tinting. The surface also contained evidence of ladder cracking. The overhauled engine was installed in April 2019 and had accumulated about 14 hours of operation before the accident. Section 7 of the Lycoming Overhaul Manual for direct drive engines, page 7-4 section 7-28A states: Crankshaft (Magnetic Particle Inspection). Inspect the crankshaft using a magnetic particle inspection procedure performed by a certified operator. The work order for the engine overhaul indicated that a magnaflux and zyglo inspection was completed, but the inspection did not include the case or crankshaft. The owner of the certified repair station stated that they perform all non-destructive testing (NDT) inspections, magna flux, and measurements for the overhauled engines at their location. After they NDT inspect the parts, “NDT” was stamped on the part. Components without an NDT stamp indicated that NDT inspection was not completed. The accident crankshaft had no visible NDT stamp.
A total loss of engine power due to a fatigue failure of the crankshaft. A contributing factor was the inadequate inspection during the engine’s last overhaul.
Source: NTSB Aviation Accident Database
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