While making a turn shortly after commencing to taxy at
Brisbane, the captain thought the nosewheel steering' felt slightly
stiffer than usual. However, during the subsequent taxying and
flapless take-off at Brisbane and the undercarriage extension at
Maryborough there were no indications of any abnormality in either
the nosewheel steering or undercarriage systems. An approach was
made to land on Runway 17 at Maryborough with a light crosswind
from the left. The aircraft touched down lightly on the main wheels
about 1,200 feet fist the threshold. The nosewheel was lowered onto
the runway and ground fine pitch was selected. Almost mediately
severe nosewheel shimmy was noticed, accompanied by vibration and
noise. The captain applied back pressure to the control column, in
order to lighten the weight on the nosewheel, and ordered the first
officer to carry out the impact drill. The severe vibration
continued, and then, at 3,100 feet beyond the threshold, the
downlock mounting lug on the nose undercarriage assembly failed
allowing the assembly to pivot rearwards beyond its normal "DOWN"
position. The captain applied the brakes as the aircraft continued
rolling with the nosewheel pivot bracket and wheel lever fork-end
skidding along the runway surface. The aircraft came to a halt 550
feet short of the southern end of the runway. Investigation showed
that the nosewheel tyre was in a substantially deflated condition
at touchdown and that the tube subsequently became mutilated and
bunched in one section of the tyre resulting in an unbalanced
nosewheel condition which generated fore and aft loads which were
at or near the natural frequency of the nose undercarriage
assembly.
