Siddique, not only the Tristar has the dual dual config, also the MD-11. Two autopilots, Cat 3B capable. A great system, and incredibly reliable. As for the other comments posted earlier, we use the left or right A/P depending on which pilot is Pilot Flying (we haven't yet adopted Nigel's system of nomenclature so we don't have Landing but Not Handling Cockpit Members), strictly as a means to exercise both sides of the house. Each F/D is tied to its respective A/P, so system monitoring is always present by the pilots, and also by the comparator.