What happened
On 5 June 2006, a Diamond Aircraft Industries DA20-C1, registration G-NIKK, was conducting a training flight at Redhill Aerodrome in Surrey. The flight proceeded normally until the pilot attempted a touch-and-go landing on the grass runway. The aircraft touched down smoothly on the main wheels, followed by a gentle placement of the nosewheel onto the surface. As the pilot applied engine power and configured the flaps for takeoff, a loud bang was heard. The aircraft stopped abruptly and violently, settling into a nose-down position. The two crew members on board were uninjured and were able to exit the aircraft without difficulty.
The investigation
An investigation by the AAIB, which included a metallurgical analysis, focused on the structural integrity of the nose landing gear. The examination revealed that the nose landing gear leg had failed due to severe plastic deformation. This deformation occurred specifically at the area just behind the weld connecting the nosewheel castoring pivot to the leg. The damage was consistent with a significant upward vertical load being applied to the nosewheel. While the investigation identified that the deformation had induced high residual tension stresses, it could not determine exactly how many flights had occurred between the initial deformation and the final structural failure.
Findings
- The nose landing gear leg failed following severe plastic deformation caused by a high upward vertical load applied to the nosewheel.
- Metallurgical analysis confirmed that the deformation led to high-stress, low-cycle fatigue cracking.
- The fracture surface showed no evidence of fatigue markers, suggesting the crack propagation occurred during a single landing event.
- The structural strength of the strut was progressively compromised by the deformation until it finally fractured under overload conditions.