In-flight structural failure leads to fatal Acroduster accident

1 fatality • 16 km north-east of Caboolture Airfield, Queensland

A fatal in-flight break-up of an Acroduster aircraft during aerobatic maneuvers has been linked to fatigue cracking in critical wing attachment components.

What happened

During an aerobatic flight, an Acroduster aircraft experienced a structural failure in mid-air, resulting in the aircraft breaking up before impacting the terrain. The accident resulted in one fatality and the total destruction of the aircraft, registered as VH-YEL. The wreckage was scattered across a 2.4 km area, with the central wing section located approximately 500 m from the primary debris field. Weather conditions at the time of the flight were not a contributing factor to the accident.

The investigation

Investigators conducted a metallurgical analysis of the upper wing centre section attachment eye bolts. While no manufacturing defects were found, the examination revealed significant pre-existing fatigue cracking within the threaded portions of the bolts. Notably, the left eye bolt showed substantial corrosion on its fracture surfaces, suggesting it had failed well before the accident flight.

Following the failure of the left eye bolt, flight loads were transferred to the left roll brace, which also exhibited fatigue cracking. The investigation determined that the remaining structural components—the right eye bolt and the left roll brace—eventually reached a critical state of fatigue and failed due to overstress. This sequence of component failures initiated the in-flight break-up.

Furthermore, the investigation found that the fatigue cracks were located in areas obscured by securing nuts and threads, making them nearly impossible to detect during standard maintenance without disassembling the attachment points. The investigation also noted that while some owners had implemented local design modifications to address known issues, there was no centralized system for the design owner to track structural trends or mandate broad-reaching improvements.

Findings

  • The primary cause of the structural failure was the failure of the left eye bolt due to fatigue cracking prior to the accident flight.
  • The subsequent transfer of loads to the right eye bolt and left roll brace led to their eventual failure under flight loads.
  • The location of the cracks made them difficult to identify during routine inspections without component removal.
  • A lack of a formal mechanism for communicating design improvements or mandatory inspection changes contributed to the risk.

Probable cause

The in-flight break-up was caused by the prior fatigue failure of the left wing centre section eye bolt, which redistributed flight loads to the remaining structural components, eventually leading to the overstress failure of the right eye bolt and left roll brace.

Frequently asked questions

What happened in the 2021-08-18 Amateur Built Aircraft ACRODUSTER II SA750 accident near 16 km north-east of Caboolture Airfield, Queensland?

A fatal in-flight break-up of an Acroduster aircraft during aerobatic maneuvers has been linked to fatigue cracking in critical wing attachment components.

Were there any fatalities in the 2021-08-18 Amateur Built Aircraft ACRODUSTER II SA750 accident?

The accident was fatal, resulting in 1 fatality.

What aircraft was involved and where did it happen?

The accident on 2021-08-18 involved a Amateur Built Aircraft ACRODUSTER II SA750, registration VH-YEL, at 16 km north-east of Caboolture Airfield, Queensland.

What was the probable cause of the accident?

The in-flight break-up was caused by the prior fatigue failure of the left wing centre section eye bolt, which redistributed flight loads to the remaining structural components, eventually leading to the overstress failure of the right eye bolt and left roll brace.

Loading the flight search…