What happened
The pilot performed a normal wheel landing; however, during the subsequent landing roll, the left main gear leg failed.
The investigation
A post-accident inspection of the aircraft revealed that the attachment bolt from the gear leg had broken into two pieces. A metallurgical examination identified three distinct fracture zones on the bolt:
- Two zones were relatively flat and propagated perpendicular to the bolt axis, which is characteristic of fatigue progression.
- One of these fatigue zones contained a heavy accumulation of oxides and corrosion deposits, suggesting the presence of an "old crack."
- The second fatigue zone was free of oxidation or deposits.
These fatigue zones accounted for approximately 75 percent of the bolt's cross section at the fracture site. The third zone displayed a fracture propagation at a 45-degree slant, which is typical of a final overstress separation. Investigators found no evidence of thread stripping on the component.
Maintenance records showed that since its manufacture in 1978, the aircraft had accumulated a total of 77 hours. The records also indicated several periods during which the aircraft had not been operated.