What happened
On 1 June 2019, a Stolp Starduster TOO SA-300, registration G-UINN, was performing a general handling and aerobatics flight at Ballyboy Airfield, Co. Meath. After completing maneuvers, the pilot attempted to land on the westerly grass runway. As the aircraft decelerated during the landing roll, the left main undercarriage leg began to gradually collapse. This structural failure caused the aircraft to veer toward the left edge of the runway. The aircraft subsequently exited the grass strip and struck a perimeter fence, with the wingtip making contact with a fencepost. The pilot and one passenger were able to exit the aircraft without assistance, and no injuries were sustained.
The investigation
Investigators examined the aircraft's undercarriage assembly and the history of its maintenance. The investigation revealed that the aircraft had previously undergone significant repairs, including a documented repair to one of the undercarriage legs. Furthermore, the investigation found that the rubber mounting pads were missing from both undercarriage housings, a condition the pilot noted may have persisted for some time.
Metallurgical analysis of the left undercarriage components showed that the horizontal brace had experienced fatigue cracking at its inner end. Evidence of rust and burnishing indicated that this failure had actually occurred prior to the flight in question. Additionally, video evidence suggested that the outer end of the horizontal brace likely suffered an instantaneous overload failure during the aircraft's take-off roll on the day of the incident, leaving the assembly held in place only by shock cords until the landing loads triggered the final collapse.
Findings
- The primary cause of the runway excursion was the collapse of the left undercarriage leg due to fatigue cracking at the inner end of the horizontal brace.
- An instantaneous overload failure of the outer horizontal and diagonal braces occurred following the initial fatigue cracking.
- The inner horizontal brace had been previously buckled, creating a point of stress concentration.
- The absence of rubber mounting pads on both undercarriage legs likely contributed to abnormal dynamic loading on the landing gear assembly over time.