History of the Flight
The aircraft had been used for training throughout the day, including circuit flying. The accident flight was a short local air experience flight. Final approach to Runway 07L was made in smooth air with 75% flap and an approach speed of 55 kt. Touchdown was smooth, with the nosewheel held off. The pilot used minimal braking, intending to vacate at the northern end. After landing, the aircraft taxied onto grass toward parking. After about 50 meters over a rough surface, the aircraft pitched forward with a cracking noise; the propeller stopped after contacting the ground. The pilot shut down fuel, magnetos, and electrical services, and informed the tower. Both occupants evacuated unhurt. It was immediately evident that the nosewheel had failed, with the forks contacting the ground and the nosegear strut bent backward.
Engineering Investigation
The nosewheel consists of two aluminum alloy halves attached to a central steel hub by five M6 allen-head bolts with Nyloc nuts. The hub, containing the wheel bearing, is mounted on a 15 mm bolt forming the axle. The wheel is centered via spacers. The hub also has five 10 mm lightening holes on the same pitch circle as the 6.5 mm mounting holes. Examination showed the wheel halves had been drilled with ten 6.5 mm holes aligning with all ten hub holes, making correct assembly ambiguous. Bolts used were fully threaded, though not considered significant. Damage indicated that during assembly, mounting bolts were inserted into the lightening holes. The wheel halves relied on clamping friction, which was insufficient; bolt movement elongated the lightening holes and caused fretting. The wheel ultimately failed due to overload at multiple mounting bolt locations, causing wheel separation from the hub. The nosewheel had been replaced by the owner about 30 flying hours prior after a puncture. No written instructions exist for nosewheel change, and no alignment markings. The replacement wheel halves had only five holes but were inaccurately drilled, making proper alignment difficult, while alignment with lightening holes was easier.
Conclusion
The nosewheel failure resulted from mis-assembly: mounting bolts inserted into larger lightening holes instead of proper mounting holes. Causal factors included wheel design allowing mis-assembly and lack of written instructions for nosewheel change.