Accident Details
During a normal wheel landing, the left main gear leg failed as the aircraft rolled along the runway. The pilot reported that the landing was performed without any anomalies prior to the failure.
Investigation Findings
Post-accident inspection of the failed gear leg revealed that the attachment bolt from the gear leg had broken into two pieces. The bolt was subjected to metallurgical examination to determine the cause of failure.
Metallurgical Examination
The specialist identified three distinct fracture zones on the bolt. Two zones were relatively flat and propagated on a plane perpendicular to the bolt axis, which is typical of fatigue progression. One of these zones was covered with heavy oxide and corrosion deposits, while the other zone was free of such deposits. The third zone displayed fracture propagation on a 45-degree slant, characteristic of a final overstress separation. The fatigue zones occupied approximately 75 percent of the bolt cross section at the fracture location. The presence of oxide and corrosion deposits on one fatigue zone suggested an 'old crack.' No evidence of thread stripping was found.
Maintenance History
Since the aircraft's manufacture in 1978, it had accumulated a total of 77 flight hours. During this period, the aircraft experienced several years in which it was not operated.