Accident Overview
On September 25, 2018, at about 1100 mountain daylight time, a Smith Aerostar 601P, registration N90339, was substantially damaged during a landing accident near Heber, Utah. The airplane was operated as a personal flight under Title 14 Code of Federal Regulations Part 91. The pilot, the sole occupant, was not injured.
Flight and Landing Sequence
The cross-country flight departed from Brigham City Regional Airport (BMC), Brigham City, Utah, at about 1030, with a planned destination of Heber City Municipal Airport (HCR). The pilot reported a normal touchdown on runway 22. During the landing roll, the airplane veered left and departed the runway surface. Despite the pilot's attempts to regain control, the right main landing gear collapsed. After exiting the airplane, the pilot observed that the left main landing gear had failed at the strut’s weld.
Postaccident Examination
The National Transportation Safety Board Materials Laboratory examined a portion of the left main landing gear assembly. The weld on the joint attached to the landing gear cylinder and upper scissor assembly had failed. The inboard fitting of the joint remained attached to the scissor assembly by a bolt, but the joint was loose where it attached to the cylinder and could be rotated against the cylinder exterior. The adjacent hexagonal cap below the loose joint remained tight against the cylinder assembly.
The attachment joint had fractured and separated along the entire circumference of the cylinder exterior, allowing the joint and linkage to rotate approximately 30° about the cylinder. The fracture surface faced upward on the strut cylinder where the joint had been welded. External weld protrusions exhibited localized deformation consistent with overstress fracture. Most fracture surface features were obliterated by smearing and grinding, consistent with post-fracture damage, indicating that the fracture existed prior to the accident. Landing gear components experience cyclic loads during landings, braking, and taxiing.
Manufacturer Input
A representative of Aerostar, the airframe manufacturer, noted that the attachment joint failure resembled a type of failure seen in a few Aerostar airplanes in the early 1970s, attributed to inadequate brazing. Following those failures, the manufacturer enhanced brazing methods and implemented x-ray inspection after furnace brazing to verify complete surface braze. The manufacturer was unaware of any recent similar failures and stated there was no specific inspection for this braze. According to the manufacturer, multiple hard landings or an opposing gear collapsing could cause the gear to fail at the braze joint from overstress. A failure of the weld renders the airplane uncontrollable on the ground.