NTSB Investigations of High-Strength Steel Landing Gear Components Fracturing from Fatigue Caused by Excessive Grinding

The National Transportation Safety Board is an independent federal agency investigating transportation accidents across aircraft, rail, pipeline, marine, highway, and hazardous materials modes. Among these events, the agency has investigated multiple accidents involving fractures of landing gear components during landing. In these cases, the failed components exhibited fatigue thumbnail cracks on the fracture surfaces, initiating at the surface. These investigations discovered that the crack initiation sites coincided with areas displaying marks consistent with excessive heating. These marks, or 'burns', develop during grinding operations when the parts are refurbished. This presentation will detail how fatigue cracks initiate at these areas of excessive grinding, the fracture morphologies observed, and the diagnosis of the issue in an investigation. The presentation will also discuss safety improvements to prevent the fracture sequence from recurring, as well as the challenges of identifying areas of excessive grinding and heat input in high-strength steel parts during rehabilitation.