Cessna 421B N380AL accident near Carlsbad, California

Probable cause

The right main landing gear collapse for undetermined reasons.

NTSB analysis

The pilot reported that touchdown on the runway and rollout were normal but that the airplane began to wobble as it decelerated to about 10 to 15 mph. He maintained directional control without braking. However, the wobble worsened, and the right main landing gear collapsed, which resulted in substantial damage to the right wing.

Postaccident examination of the airplane revealed that the right main landing gear torque link pivot bolt assembly was severed, and the two inboard spacer washers, nut, and cotter pin were not located. Additionally, the the landing gear trunnion was partially separated from the wing structure. Vertical scuffing was observed on the outboard crown of the right main landing gear tire, which is consistent with the wheel skidding along the ground after becoming misaligned about 90° from normal. Metallurgical examination of the torque link pivot bolt revealed that the bolt fractured through the threaded region at the edge of the pivot barrel in bending overstress, with no evidence of preexisting cracking or corrosion. In addition, the trunnion fractured in overstress, with no evidence of preexisting fatigue cracks or fractures.

Alignment of the wheel is achieved by washers installed between the upper and lower torque link assemblies; disconnection of the upper and lower torque link assemblies from one another could result in wheel misalignment, vibration, and ultimately failure of the main landing gear. However, due to postaccident damage to the landing gear and the unrecovered components, there was insufficient evidence available to determine why the right main landing gear collapsed.

Text from the NTSB. Open the NTSB docket for WPR17LA131 for the full record.