What happened
On October 8, 2020, at approximately 11:30 UTC, a PZL 106-BT-601, registration LV-BDY, was performing aerial application work near Suipacha, Buenos Aires. While the pilot was executing a left turn to align with a spraying swath, the aircraft suffered a sudden loss of control. The failure of a vertical stabilizer attachment fitting caused the aircraft to develop a continuous left yaw. The pilot was forced to perform an emergency landing in an unprepared field. The pilot sustained no injuries, though the aircraft suffered significant damage to the fuselage, the right wing tip, the main landing gear, and the vertical stabilizer hardware.
The investigation
The Argentine Transportation Safety Board (JST) conducted a technical analysis of the hardware components involved in the failure. Laboratory testing of both the left and right attachment fittings revealed that the failure was driven by fatigue-induced crack propagation. While investigators looked for external triggers such as corrosion or surface damage, no such evidence was found.
Detailed fractographic analysis showed that the cracks originated on the same face of both fittings, a pattern characteristic of variable bending stresses. The investigation determined that the right fitting failed first due to higher stress concentrations at specific hole positions. As cracks developed, the effective load-bearing area of the metal decreased, eventually leading to the final structural collapse of the component.
Findings
- The structural collapse of the right vertical stabilizer attachment fitting caused the loss of directional control.
- The failure mechanism in the left fitting was identical to that of the right fitting.
- The cracks progressed through a mechanism of fatigue-induced crack propagation.
- The location of the crack initiation point, situated within the junction area of the rivets and the vertical stabilizer structure, made the damage extremely difficult to detect during standard inspections.
- The existing maintenance manual included routine inspections for the tail section but lacked specific tasks or criteria to identify this particular type of progressive fatigue failure.
Safety action
Following the investigation, a safety recommendation (RSO AE-2044-24) was issued to the manufacturer, Airbus Poland S.A. The recommendation advises the incorporation of specific inspection items into the aircraft maintenance program or the implementation of necessary measures to detect and contain the progressive spread of cracks in the vertical stabilizer attachment hardware to prevent future loss of control.