N151VR

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 the landing 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.