N90339Smith AEROSTAR 601P · 1975

On September 25, 2018 about 1100 mountain daylight time, a Smith Aerostar 601P, N90339, was substantially damaged when it was involved in an accident near Heber, Utah. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The personal cross-country flight departed from Brigham City Regional Airport (BMC), Brigham City, Utah, about 1030 with a planned destination of Heber.

The pilot stated he touched down normally on runway 22 at Heber City Municipal Airport (HCR), Heber, Utah. During the landing roll, the airplane veered left and continued off the runway surface. Despite his attempts, the pilot was unable to regain control, and the right main landing gear collapsed. Upon egressing the airplane, the pilot observed that the left main landing gear had failed at the strut’s weld, and the airplane sustained substantial damage to…

Postaccident examination of a portion of the left main landing gear assembly by the National Transportation Safety Board Materials Laboratory revealed that the weld had failed on the joint attached to the landing gear cylinder and upper scissor assembly. The inboard fitting of the joint remained affixed to the scissor assembly by an attachment bolt. The joint was loose where it attached to the cylinder, and it could be rotated against the cylinder exterior. The adjacent hexagonal cap below the loose joint was still tight against the cylinder assembly (see figure).

Figure: Diagram and forward aft view picture of the left main landing gear

The attachment joint had fractured and separated about the entire circumference of the cylinder exterior. This separation allowed the joint (and linkage) to rotate approximately 30° about the cylinder. The fracture surface of the attachment joint faced upward on the strut cylinder where the joint had been welded to the cylinder. Examination of the joint portions of the fracture surface, particularly along the fractured weld protrusions, did not reveal any fracture features. Portions of the external weld on the joint exhibited features of localized deformation, all of which were consistent with overstress fracture. Most of the fracture surface features had been obliterated by smearing and grinding, consistent with post fracture damage. The degree of the fracture surface damage was consistent with the fracture and separation existing prior to the accident. Landing gear components are under cyclic loads at every landing and during landing actions (such as braking or taxiing).

According to a representative of Aerostar, the airframe manufacturer, the attachment joint failure looked like the same type of failure that a few Aerostar airplanes had in the early 1970s because of an inadequate braze joint, which allowed the landing gear to rotate. Following those failures, the manufacturer enhanced the brazing methods and performed an x-ray inspection after furnace brazing to verify that the surface braze was complete. The manufacturer was not aware of any recent failures occurring in this area and there is not a specific inspection for this braze and further stated that, with multiple hard landings or an opposing gear collapsing, the gear could fail at the braze joint from overstress. A failure of the weld makes the airplane uncontrollable on the ground.