What happened
On May 26, 2020, a private pilot was conducting a technical flight at Rybnik Airport (EPRG) to inspect an ultralight Sirius TL-3000 following a 45-day period of inactivity. During the flight, the pilot performed functional checks of the flaps and the propeller governor at an altitude of 3,500 ft.
Upon completing the flight, the pilot landed on runway 30°. While taxiing to exit the runway, the pilot noticed that the aircraft was not responding to rudder inputs and was forced to use differential braking to steer toward the hangar. After exiting the cockpit, the pilot observed that the nose of the aircraft was sitting lower than usual and discovered that the propeller blade tips had sustained damage. There were no injuries to the pilot.
The investigation
The PKBWL investigation focused on the structural integrity of the landing gear and the extent of the damage to the aircraft. Upon removing the engine cowlings, investigators identified a fatigue crack on the upper portion of the front landing gear strut. The crack was located along the welded junction between the strut tube and the reinforcement tube at the upper mounting point.
Examination of the weld revealed poor workmanship, characterized by an irregular bead, pitting, and evidence of grinding. Furthermore, the investigation established that the metal had been overheated in several areas during the welding process, which compromised the material's strength. The damage to the aircraft included a broken front landing gear strut, a damaged propeller, and cracks in the composite elements near the strut mounting area.
Findings
- The primary cause of the incident was a fatigue crack in the front landing gear strut at the welded junction near the upper mounting.
- The structural failure was exacerbated by the weakened strength of the material near the weld, caused by localized overheating during the welding process.
- The failure of the strut caused the aircraft's nose to drop, leading to direct contact between the propeller blades and the runway surface.