What happened
On 7 September 2007, an instructor and a student were conducting a series of touch-and-go training circuits at Abbeyshrule airfield in Co. Longford. The aircraft, an Urban-Air UFM10 Samba with registration EI-DRM, had successfully completed several circuits without issue. However, during the final landing of the session, the aircraft rolled along the runway before a sudden vibration occurred and the nose dropped approximately 4 inches.
The instructor immediately took control, pulling back on the stick to prevent further descent. The aircraft briefly lifted 4 to 6 feet off the runway surface. To mitigate the situation, the instructor reduced the throttle to idle and shut down the engine. The aircraft traveled an additional 150 metres down the runway before touching down again. The instructor continued to hold the stick back to keep the nose off the ground, but the aircraft eventually skidded for another 150 metres before coming to a complete stop. There were no injuries to the two occupants, though the aircraft sustained minor damage to the propeller tips and the nose gear.
The investigation
Investigators examined the structural integrity of the nose undercarriage and the history of the aircraft. The Urban-Air UFM10 Samba had been in service for approximately 1,337 hours, primarily used for flight training.
Upon inspecting the nose gear, investigators found that the strut had partially collapsed at its weakest point. The examination of the fork unit revealed that the failure occurred at the plug welds where the internal sleeve meets the steering tube. The investigation identified evidence of corrosion and weld slag at these specific locations. Furthermore, it was noted that the aircraft's use as a trainer likely subjected the airframe to frequent high landing forces over its service life.
Findings
- The primary cause of the incident was the fracture of the nose wheel steering tube near its weakest point.
- The failure occurred at the circumference of the tube where the three plug welds are located, rather than at the designed fracture point.
- Internal corrosion and the presence of weld slag may have contributed to the structural weakness.
- The aircraft's history of intensive training use likely resulted in repeated high-impact landing forces on the nose gear.
- Directional control of the aircraft was lost during the landing roll following the structural failure.