What happened
On November 6, 2021, an AN-2 aircraft, registration YR-PMW, operated by ASC Skydiving Center, was involved in an accident at the Letca Nouă landing field in Giurgiu County, Romania. The flight was a scheduled skydiving operation. After completing the jump mission and returning to the airfield, the aircraft landed on runway 21 at approximately 11:35 LT.
During the subsequent taxiing phase, the aircraft began to tilt heavily to the right. The pilot attempted to correct the movement by applying left aileron, believing a tire failure had occurred. However, the tilt continued until the tip of the right lower wing spar struck the ground, causing the aircraft to pivot 180 degrees from its original direction of travel. There were no injuries to the two crew members on board.
The investigation
The investigation focused on the structural integrity of the landing gear following the visible damage to the right main gear strut and the wing spar. Investigators examined the broken rear brace of the right main landing gear.
Technical analysis revealed that the broken brace had been subjected to unauthorized welding repairs near the attachment point with the strut. Metallographic examination showed that these weld points had induced micro-structural changes and altered the stress fields within the heat-treated steel. This process created micro-cracks and increased residual stresses, which eventually led to a sudden failure under bending and tension loads.
Findings
- The primary cause of the accident was the failure of the right main landing gear strut due to the breakage of the rear brace.
- A significant contributing factor was the performance of non-compliant repairs on the brace using welding, which is strictly prohibited by the manufacturer's maintenance instructions; the manual requires complete replacement of braces if cracks are detected during non-destructive testing (NDT).
- The application of welding to this specific heat-treated steel caused detrimental micro-structural changes and increased internal stress levels.
- While the aircraft had undergone NDT inspections as recently as April 2021, the unauthorized repair was not documented in the maintenance records, making it impossible to determine when the improper welding occurred.