What happened
On 11 November 2001, a CEA DR400/180R, registration G-BJUD, was performing a private flight at Lasham Airfield, Hampshire. The flight was intended to be the first of three visual circuits to maintain the pilot's currency for glider towing operations.
During the landing on Runway 27, the pilot maintained a high nose attitude using elevator input to utilize aerodynamic braking while applying moderate wheel brakes. As the aircraft's speed decreased and the nose wheel contacted the ground, a significant shimmy developed. In an attempt to dampen the vibration, the pilot moved the control stick forward to engage the nose wheel steering mechanism. At this moment, the nose landing gear collapsed. The impact caused the four-bladed wooden propeller to strike the asphalt, which subsequently stopped the engine. The aircraft slid along the runway, coming to rest halfway between the centerline and the left edge. There were no injuries to the pilot.
The investigation
An investigation by the AAIB included an examination of the aircraft's nose landing gear (NLG) and a metallurgical analysis of the fracture surfaces. The investigation focused on the upper support bracket of the NLG, which had failed.
Investigators found evidence of fatigue cracks originating at the narrow sections of the bracket. One crack had progressed significantly, turning vertically down the wall of the oleo strut, with corrosion suggesting the crack had been present for a long duration. The investigation also identified a non-standard weld on the upper side of the bracket. While the manufacturer's drawings specify that the bracket should only be welded on the lower side, this bracket featured an additional sealing weld. This weld was found to be of poor quality, characterized by excessive gas porosity and poor penetration into the parent material.
Findings
- The nose landing gear collapsed due to the detachment of the upper support bracket.
- Fatigue cracks had developed in the narrow sections of the bracket.
- The structural integrity of the bracket was compromised by poor quality and non-standard welds that failed under normal landing loads.
- A previous repair to the lower bracket in July 2000 involved a weld repair rather than returning the unit to the manufacturer as required by Service Bulletin 101; if the unit had been sent for professional repair, the fatigue cracks in the upper bracket might have been detected.