What happened
On October 8, 2020, at approximately 11:30 UTC, a PZL 106-BT-601, registration LV-BDY, was performing an aerial application flight near Suipacha, Buenos Aires province. While the pilot was executing a left turn to align with a spray swath, the aircraft experienced a sudden loss of control. This was caused by the failure of one of the attachment hardware components of the vertical stabilizer. The failure resulted in continuous left yaw, forcing the pilot to perform an emergency landing in an unprepared field. The pilot sustained minor injuries, and while the aircraft suffered significant damage to the fuselage, wing tip, and landing gear, there were no fatalities.
The investigation
The investigation focused on the mechanical failure of the vertical stabilizer attachment hardware. Laboratory testing was conducted on both the left and right hardware components. The analysis examined the presence of surface defects, corrosion, or stress concentrators that might have initiated the failure. Investigators also reviewed the aircraft's maintenance records and the manufacturer's inspection protocols to determine if the defect could have been detected during routine service.
Findings
- The failure was caused by fatigue-induced crack propagation within the attachment hardware.
- Macro-fractographic analysis revealed that the cracks originated due to bending stresses acting on the hardware.
- The failure mechanism began at the junction with the rivets of the vertical stabilizer structural assembly, a location that makes the cracks difficult to detect during standard inspections.
- While the aircraft maintenance manual includes routine inspection items for the tail section, the existing procedures do not include specific tasks capable of identifying this particular type of progressive fatigue failure.
- No significant material differences or external factors like corrosion were found between the two hardware pieces.
Safety action
- RSO AE-2044-24: It is recommended that the manufacturer, Airbus Poland S.A., incorporate specific inspection items into the aircraft maintenance program or implement necessary measures to detect and contain the progressive advancement of cracks in the vertical stabilizer assembly hardware.