What happened
On 7 April 2010, an Extra EA 300, registration G-SIII, was performing a private flight at White Waltham Airfield in Berkshire. The approach to Runway 29 was uneventful, and the touchdown and initial landing roll proceeded normally. However, after the brakes had been applied, the tail of the aircraft began to lift. As the pilot attempted to correct the aircraft's attitude by moving the control column rearwards, the aircraft dropped to the right. This caused the propeller blades to strike the ground several times, and the aircraft veered toward the right side of the runway before coming to a halt.
During the landing roll, the right mainwheel assembly detached from its axle. This separation caused the right landing gear leg to drag along the ground, creating a gouge in the grass runway. The incident resulted in damage to the right landing gear, the propeller blades, and the right aileron, but there were no injuries to the two occupants.
The investigation
Investigators examined the aircraft's landing gear and the condition of the runway. The right axle and mainwheel assembly had detached from the gear, while the left axle remained attached. The landing gear leg itself showed signs of failure at the point where it attaches to the right side of the fuselage, consistent with being dragged along the ground.
Maintenance records showed that the landing gear had been removed 65 flying hours prior to the accident, at which time the axles were refitted using the existing nuts and bolts. While the manufacturer's policy is to replace these fasteners during such work, no such instruction existed in the aircraft's maintenance manuals.
An examination of the four fasteners on the right axle revealed they were bent and the threads were severely damaged. Scanning electron microscopy (SEM) indicated that the thread damage was consistent with an overload failure in a ductile manner, suggesting the nuts had been pulled from the bolts. However, the investigators could not determine the specific cause of this failure, as the threads were too damaged to show evidence of prior cracking.
Findings
- The right mainwheel assembly detached because the four fasteners securing the axle to the landing gear failed.
- The failure was likely caused by the nuts being pulled from the bolts due to an overload.
- The runway surface at White Waltham is known to be rough and undulating, which can cause significant flexing of the landing gear legs.
- This flexing may have generated a large side force on the tyres, contributing to the failure.
- There was no evidence that the nuts had previously loosened or unwound.
Safety action
- Safety Recommendation 2010-046: It is recommended that the Extra Aircraft Company advise owners and update maintenance manuals to mandate that new nuts and bolts must be used whenever the wheel axles are replaced or refitted to the landing gear.