Primary finding
Probable cause
The total loss of engine power due to a fatigue fracture of the crankshaft.
Investigator assessment
Analysis narrative
The pilot reported that after takeoff from runway 23, about 466 ft above ground level, the engine “failed,” and he immediately turned back to land. The pilot landed with a direct gusting tailwind and applied hard braking; however, a gust of wind lifted the right wing, and the airplane exited the left side of the runway. The left wing struck a taxiway sign, which resulted in substantial damage to the left wing. A postaccident examination of the engine revealed that the crankshaft was fractured aft of the No. 2 connecting rod journal. The fracture surface exhibited signatures consistent with fatigue cracking that originated from multiple initiation sites along the radius between the connecting rod journal and the crankshaft web.
Source record
Factual narrative
On November 6, 2020, about 1158 Pacific standard time, an experimental amateur-built Vans RV-12 airplane, N975G, was substantially damaged when it was involved in an accident near Byron, California. The pilot and passenger were uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that after takeoff from runway 23, at approximately 466 ft above ground level, the engine failed, and he immediately initiated a left turn toward runway 5. The pilot stated that upon completing the 180° turn, he encountered a gusting tailwind, which increased his airspeed of 65 knots to a groundspeed of about 85 to 88 knots. Concerned he would run off the end of the runway, he landed, “braked hard, and was slowing [the airplane] straight on the runway”when a gust of wind lifted the right wing, and the airplane exited the left side of the runway. The left wing struck a taxiway sign, the nose gear sheared off resulting in substantial damage to the left wing. The pilot reported that at the time of takeoff, the wind was from 230° at 18 knots with gusts to 23 knots. A postaccident examination of the UL Power UL350iS engine revealed that the crankshaft was separated aft of the No. 2 connecting rod and forward of the No. 3 main bearing journal. The separated portions of the crankshaft were sent to the National Transportation Safety Board Materials Laboratory for further examination. The examination revealed the crankshaft had fractured just aft of the No. 2 connecting rod journal and forward of the crankshaft web (see figure). Figure. – Crankshaft Ratchet marks, consistent with multiple crack initiation sites, were present particularly near the initial areas of the fracture, located along the edge of the fracture surface at the radius near the connecting rod journal surface. A series of repeating crack arrest marks along with microscopic fatigue striations, consistent with fatigue crack propagation, was observed within the fracture surface. Additionally, the journal surface exhibited circumferentially oriented microscopic gouge marks, which were present up to the edge, as well as near one fatigue crack initiation site.