WPR22LA357

According to the pilot, when the airplane reached 15-20 knots (kts) during the initial takeoff roll, the left main landing gear collapsed, and the airplane ground looped to the left. The airplane sustained substantial damage to the left elevator and left wing. Examination of the left main landing gear (MLG) leg determined it fractured due to preexisting cracks that initiated at the inboard side of the leg at the forward and aft sides of the forward hole for attaching the leg to the fuselage at the outboard attachment bracket. Examination of the crack revealed it existed before the accident flight; however, spacing between crack arrest features suggest the number of load cycles from initiation to failure was relatively low. A review of available flight data did not reveal a specific hard landing event that could have resulted in the initiation of the crack. The airplane’s main landing gear is made from a woven E-glass with epoxy resin and prepreg laminate that is pressed and then oven cured. The raw material is not aviation specific. Destructive testing of the failed landing gear and material samples from other gear manufactured from the same lot of material found the material did not meet minimum specified strength requirements. The material batch in question was traceable to 16 airplanes (30 gear legs), including 1 other airplane that had a similar failure following a hard landing. The owners of the affected airplanes were notified and the landing gear for some of the affected airplanes were replaced. Following this accident, the airplane manufacturer initiated a redesign of the landing gear and began performing destructive batch sample tests of the composite material used for every batch of gear legs to ensure each new gear leg meets minimum required strength requirements. The accident is consistent with the landing gear being manufactured using material that did not meet the necessary strength requirements and subsequently failing after a crack developed in the landing gear. The event that initiated the crack was not identified based on available evidence.

On September 27, 2022, about 1458 mountain standard time, a Vashon R-7, N151VR, was substantially damaged when it was involved in an accident near Glendale, Arizona. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, he was aligned with the runway heading and applied power for takeoff. When the airplane reached 15-20 kts, the left main landing gear (MLG) collapsed, and the airplane ground looped to the left. The airplane sustained substantial damage to the left elevator and left wing. The airplane was equipped with a Dynon Skyview HDX avionics unit, which can record a limited number of flight and performance parameters, including vertical acceleration (g’s). The unit collected data at both a 4hz (4x/sec) and 16hz (16x/sec) rate and recorded the data as separate files. A review of the recovered data indicated the highest recorded vertical acceleration within the recovered data that could be associated with a landing event was 1.7g. Each gear leg has four holes in the upper section of the leg where an inner and an outer MLG bracket is bolted to facilitate mounting the gear leg to the fuselage structure (see Figure 1). The left gear leg from the accident airplane was fractured where it had attached to the fuselage at the outboard bracket (Figure 2). Figure 1 – Gear Engineering Drawing Figure 2 – Left Gear Fracture (Pilot Photograph) The left gear leg was examined by the National Transportation Safety Board Materials Laboratory. The fracture surface intersected the middle of the attachment bolt holes at the inboard side of the fracture and through most of the thickness near the outboard edge. The fracture shifted downward toward the lower end of the outboard bracket faying surface. The fracture surface near the inboard edge of the fracture was relatively smoother in a translaminar plane with limited interlaminar fractures. The fracture surface had a rougher appearance near the middle of the fracture and toward the outboard edge of the fracture with increased interlaminar fractures and variable fracture path through the thickness. A portion of the fracture surface had a flattened appearance. Subsequent examination of the area using a scanning electron microscope revealed indications of progressive crack growth. The airplane’s MLG is produced from NP 130HF, a woven E-glass w/epoxy resin, prepreg laminate that is pressed and oven cured. The raw material is supplied from a non-aviation specific manufacturer in a cured 4'W X 8'L X 13/16" thick sheet, and is waterjet cut into shape. A vinyl wrap is installed to the exterior of the leg to provide UV protection. The lengthwise direction of the gear leg is cut out of the warp (0°) orientation of the sheet for the greatest flexural strength, which is advertised to be 85 ksi. It was determined that there was a batch of 16 airplanes, serial numbers 10140-10155, with a potential material strength inadequacy of thelanding gear, realized by main landing gear fractures that occurred on 4 of these airplanes. Two of the occurances of a failed landing gear followed a hard landing event. One of those events was classified as an accident (National Transportation Safety Board acccident ERA21LA158). Twenty-five flexural destructive tests were performed using specimans from remnants of the batch of NP 130HF material from which the failed landing gear were produced, material from the failed landing gear itself, and specimans from the gear of several serial airplanes from the same batch of material. The average flexural strength for the samples tested was 70.2 ksi. Following the destructive tests, Vashon Aircraft issued inspection guidance to the owners of airplanes in service with landing gear manufatured from the batch of NF 130HF in question, began destructive flexural testing of each new batch of material used to manufacture gear legs to ensure strength standards are met, and began evaluation of a redesign of the landing gear.