S'right Scooby. Thats the definition of 'Fail Operational' and why you can perform a CatIII landing with a 'Fail Operational' AFCS but not with one that has degraded to 'Fail Passive'. A Boeing will tell you as far down as 1500 feet if one channel is voted out, by annunciating 'No Land 3' but after 1500 feet will keep that information to itself until below 80 knots on the roll out. I know of no AFCS with less than three channels that may perform a CatIII Approach and landing. Two channels and you're restricted to CatII at best - i.e. see the runway at minimums or b*gger off somewhere else. Of course 'channels' is not the same thing as 'Autopilots'. You might for instance say that a B767 has only one autopilot with three channels but really its a Triple Channel AFCS with integrated Autopilot, Flight Director and Autothrottle functions.
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Through difficulties to the cinema