What happened
On December 31, 2018, an EXTRA 300L operated by a private owner took off for a flight within the airport traffic zone at Katowice Muchowiec (EPKM). After approximately seven minutes of flight, the pilot transitioned to a landing configuration on runway 05.
During the final phase of the landing rollout, the right main landing gear strut fractured at the point where it attaches to the fuselage. This failure caused the aircraft to tilt toward the right and begin a sharp veer. The pilot was unable to correct the loss of directional control, and the aircraft rotated approximately 240 degrees to the right before coming to a stop on the runway.
During this rotation, the left main landing gear strut broke due to centrifugal and inertial forces. The resulting shift in the aircraft's posture caused the propeller blades to strike the runway surface, resulting in damage. Additionally, the left aileron balance was bent during the event. There were no injuries to the pilot or the passenger.
The investigation
The PKBWL examination focused on the structural integrity of the landing gear and the sequence of the ground excursion. Investigators inspected the aircraft in a hangar and identified that the right strut had failed at its fuselage mounting point.
Technical analysis of the fracture surfaces revealed that the break in the left strut was a sudden, non-fatigue failure caused by the intense forces of the rotation. Furthermore, investigators noted that the transition from a concrete surface to an asphalt surface likely contributed to the rotation. Because concrete provides a higher coefficient of friction than asphalt, the left wheel—which entered the asphalt first—experienced less grip than the right wheel, which was still on the concrete. This difference in friction, combined with the braking effect of the failing right gear, created a torque sufficient to initiate the aircraft's spin.
Findings
- The primary cause of the incident was the fracture of the right main landing gear strut at its attachment point to the fuselage during the landing rollout.
- A mechanic familiar with the EXTRA 300L noted that this specific location is a known area prone to fatigue cracking in this aircraft type.
- The change in runway surface from concrete to asphalt contributed to the loss of directional control by creating an asymmetrical friction force between the left and right wheels.