Accident Overview
On June 22, 2017, at about 1325 Pacific daylight time, a Cessna 421B, registration N380AL, was substantially damaged in an accident at McClellan-Palomar Airport (CRQ) in Carlsbad, California. The two pilots aboard were not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as an instructional flight.
Flight History
The pilot receiving instruction reported that this was the airplane's first flight after an extended maintenance period. The flight initially proceeded to Ramona, California, where an uneventful landing was performed. Subsequently, the aircraft flew to McClellan-Palomar Airport.
Landing and Gear Collapse
According to the pilot, touchdown on runway 24 and the rollout were normal. As the airplane decelerated to about 10 to 15 mph, it began to wobble. The pilot maintained directional control without applying brakes, but the wobbling intensified. Suddenly, the right main landing gear collapsed, causing the right wing and engine to strike the ground, resulting in substantial damage to the wing.
The flight instructor stated that the approach and landing were normal and that after touchdown, the airplane decelerated "nicely." Just before reaching taxiway A5, he noticed a sensation resembling a flat tire or oscillation in the landing gear and asked the pilot to "keep it straight." The pilot responded that he was not going to brake. A few seconds later, the right main landing gear collapsed, and the airplane rotated toward taxiway N3. The instructor estimated the airplane's speed during the gear oscillation was between 5 and 10 mph.
Postaccident Examination
Examination of the right main landing gear revealed that the torque link pivot bolt assembly was severed. The two inboard spacing washers, nut, and cotter pin were missing. The landing gear trunnion was partially separated from the wing structure, and the right main landing gear was separated but remained attached via hydraulic hoses.
The forward right landing gear trunnion had separated into two pieces, with the lower portion torn away from the upper portion. Scraping was observed on the outboard side of the landing gear strut and brake caliper. The right main landing gear tire exhibited vertical scuffing along its outboard crown, and additional multidirectional striations were present on the outboard portion of the lower torque link assembly, brake caliper, and lower portion of the landing gear strut assembly.
Components including portions of the right landing gear trunnion, right landing gear brace assembly, upper torque link assembly, and torque link pivot bolt were sent to the National Transportation Safety Board Materials Laboratory for metallurgical examination. The torque link pivot bolt was found fractured through the threaded region at the edge of the pivot barrel. The fracture surface was partially obscured by red rust deposits but exhibited surface texture, topography, and deformation patterns indicative of a bending overstress fracture. No indications of preexisting cracking or corrosion were identified. The trunnion pieces and other submitted parts displayed fractures consistent with overstress, with no evidence of preexisting fractures or fatigue cracks.