What happened
On 26 September 2003, a Robin DR400/180 Regent, registration G-FTIL, was conducting a private flight to Little Staughton Airfield for scheduled maintenance. The weather conditions were clear with good visibility. Shortly after the aircraft completed a routine landing on Runway 25, the nose landing gear suddenly collapsed, causing the aircraft to veer sharply to the left. The impact caused the propeller to strike the ground and the engine to suffer a shock load. The aircraft slid approximately 20 metres before coming to a stop near the edge of the runway. There were no injuries to the pilot or the passenger on board.
The investigation
Investigators examined the nose landing gear and identified a potential fatigue failure near the upper support plate. A detailed metallurgical analysis confirmed that a fatigue failure had occurred within the narrow strap section of the upper support plate. This failure was driven by standard in-service loads and the separation of the fillet weld connecting the upper support plate to the outer cylinder.
Further inspection of the weld revealed significant defects, including gross gas porosity throughout the circumference and inadequate cross-sectional dimensions for the joint. The investigation determined that this was the original weld applied during the manufacturing process using the Gas Tungsen Arc Welding (TIG) method. The replacement nose landing gear unit, which had been installed following a previous accident in 1993, had completed roughly 2,700 landings before the failure occurred.
Findings
- The nose landing gear collapsed due to a fatigue failure in the upper support plate strap section.
- The failure was caused by the separation of the original manufacturing weld.
- The weld was of poor quality, characterized by excessive gas porosity and insufficient dimensions.
- Existing mandatory inspections, mandated by Service Bulletin 101 and Airworthiness Directive 83 206(A)R3, focused only on the lower support plate and did not require inspection of the upper support plate.
Safety action
- It is recommended that the manufacturer, Apex Aviation, update Service Bulletin 101 to include inspections of the upper support plate.
- It is recommended that the DGAC (France) re-issue the relevant Airworthiness Directive to include the upper support plate in inspection requirements.
- It is recommended that the DGAC assess the welding standards used by Apex Aviation to ensure compliance with European and French aerospace requirements.