What happened
On April 11, 2011, a Robin DR 253, registration F-BOZM, was performing a flight from Nangis to the Pont sur Yonne aerodrome with two passengers on board. The pilot executed a normal landing on the unpaved runway. However, while taxiing a few meters along the runway, the aircraft's nose gear suddenly failed, causing the aircraft to collapse forward. The aircraft sustained heavy damage as a result of the impact.
The investigation
Investigators examined the nose gear assembly following the incident. Upon disassembly, it was discovered that the lower mounting plate had fractured at the weld bead connecting it to the nose gear strut. Fractographic analysis revealed penetration defects within the weld circumference that joined the lower plate to the strut. These defects allowed fatigue cracking to initiate under the cyclic stresses experienced during landing and taxiing operations. Similar damage, though not yet resulting in a complete break, was also identified on the weld connecting the upper plate to the strut.
Findings
- The primary cause of the accident was welding penetration defects that reduced the effective load-bearing area of the weld bead.
- This reduction in strength rendered the weld incapable of withstanding standard operational stresses, leading to the structural failure of the lower plate.
- The investigation noted that existing safety protocols, specifically EASA Airworthiness Directive EU-2010-0231, were ineffective in this instance. While the AD required dye penetrant inspections every 100 hours to detect cracks, the specific fatigue cracks in this component propagate from the inside out. Because these cracks do not reach the surface, they remain undetectable by surface-level inspection methods until they reach a terminal stage.