What happened
On 12 September 2008, an Extra EA 300, registration G-SIII, was performing a private flight at White Waltham Airfield. Following a standard approach and touchdown, the aircraft was in its landing roll when the left landing gear leg fractured. This structural failure caused the wheel assembly to detach from the leg, resulting in the aircraft veering uncontrollably to the left. The aircraft swung through approximately 180 degrees before coming to a halt. The pilot and passenger were able to exit the aircraft quickly after all services were shut down; no injuries were sustained by either occupant.
The investigation
Investigators examined the wreckage and the complete left main landing gear assembly, which had broken away from the aircraft. Detailed engineering analysis conducted by QinetiQ revealed that the failure of the left leg was the result of two distinct processes. First, the brake caliper had been abrading the paint and the outer glass fabric layer of the composite material. Second, lateral flexing of the leg during taxiing, takeoff, and landing caused cracks to develop around the metal flange plate.
These breaches in the outer composite layer allowed contaminants, including moisture, brake dust, and an oil-based fluid likely to be hydraulic fluid, to penetrate the internal structure. The ingress of these substances caused the plywood core of the leg to swell, which subsequently triggered further cracking in the outer layers. This progressive degradation eventually led to a lateral failure of the structure under load.
Findings
- The primary cause of the failure was the progressive weakening of the composite landing gear leg due to environmental contamination and structural fatigue.
- Abrasion by the brake caliper at the lower rear of the leg exposed the glass fibre fabric to the elements.
- The ingress of liquids and solids caused the internal plywood core to expand, creating internal stresses that propagated cracks through the outer composite layers.
- The aircraft was fitted with an older design of the composite U-shaped carrier, which had been superseded by a redesigned version by the manufacturer.
- Inspection of the right landing gear leg showed similar signs of abrasion and staining, suggesting a shared failure mechanism across the fleet.