Regarding Delta (NW) A330
The problem I suspect is the pitot tubes ice over and you loose your airspeed indication along with the auto pilot, auto throttles and rudder limit protection. The rudder limit protection keeps you from over stressing the rudder at high speed.
It sounds like this oversimplifys what may happen in terms of the rudder limiting.
Per the A330 FCOM Flight Controls Description:
"Rudder and pedal deflection is limited as a function of the speed. Each limiter channel is controlled and monitored by its associated SEC. In case of double SEC failure, the max rudder deflection remains at the value reached before failure ; then, a max deflection is available when the slats are extended."
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