Accident Overview
On September 6, 2019, at 1230 central daylight time, a Cessna 195A airplane, registration N9895A, impacted terrain after veering off runway 30 at Pocahontas Municipal Airport (POH), Pocahontas, Iowa. The airplane sustained substantial damage. The airline transport pilot and a passenger were uninjured. The airplane was registered to and operated by the pilot under Title 14 Code of Federal Regulations Part 91 as a personal flight not operating on a flight plan. Day visual meteorological conditions prevailed at the time. The flight originated from Bismarck Municipal Airport (BIS), Bismarck, North Dakota, and was destined for POH.
Landing Event
The pilot stated that the wind was from the north and he determined runway 30 was appropriate for landing. During the landing touchdown, he immediately felt a shift to the left. The left main landing gear separated and collapsed, causing the airplane to go off the runway. The airplane came to a stop with only the tail remaining on the runway.
Damage Examination
The airplane sustained substantial damage, including wrinkling and upward bending of the left wing. The fractured left main landing gear spring strut was shipped to the National Transportation Safety Board Materials Laboratory for examination. The spring strut fractured at approximately 7 inches from the inboard edge on the forward side and approximately 6 inches from the inboard edge on the aft side. A light gray paint coating appeared over the entire part surface, and a darker gray paint coating was present only on the outboard piece with a clearly delineated inboard boundary. Both gray coatings were chipped and absent from numerous locations, exposing areas of underlying light gray coating as well as areas of brownish-red oxidized metal. A visibly distinct band of brighter light-gray coating and exposed oxidized metal was apparent on the upper and lower surfaces of the spring strut on both sides of the fracture. The upper surface was visibly smoother than the lower surface, which exhibited a dimpled texture.
Fracture Analysis
The mating outboard fracture surface exhibited significant post-fracture mechanical damage and oxidation, obscuring some finer fracture details. The fracture origin was located on the upper surface at the forward edge of the spring strut. Chevron marks radiated outward from this location along the upper surface and toward the lower surface, consistent with an aft and downward crack propagation direction. Closer examination of the origin area revealed a small discolored thumbnail-shaped crack and ratchet mark features consistent with fatigue cracking from multiple origins. The upper surface adjacent to the thumbnail-shaped crack at the fracture origin was absent of gray coating and had exposed oxidized metal over an area approximately 1 inch inboard of the fracture surface and about 0.75 inch aft of the forward edge. This area was pitted and rougher than the surrounding upper surface where gray coating was intact. Reddish-orange staining was also observed near the fracture origin on the surrounding gray coating.
The thumbnail-shaped pre-existing crack region was relatively flat and smooth compared to the rest of the fracture surface. Crack arrest lines were evident progressing from at least three origins separated by two visible ratchet marks. Smaller, semi-elliptical sections bounded by crack arrest lines within the thumbnail crack were brownish-red in color, progressively lighter away from the origins. The pre-existing crack measured approximately 0.131 inch along the upper surface of the spring strut and extended about 0.058 inch into the part. The fracture surface morphology outside the thumbnail-shaped pre-existing crack was dull and rough, consistent with overstress separation. The loads experienced by the landing gear during the accident landing are unknown, and a structural analysis was not performed to determine if the loads exceeded design load limits.