Depends if you are doing a Cat 3B (no DH) approach or just a CAT 3B approach. 3B no DH requires no visual reference and a normal CAT 3B requires 1 centreline light. Depends if you have Fail Operational (no DH) or Fail Passive (with DH) autopilots available. On 744 3 autopilots means no DH and if you lose 1 and become Land 2 you use 3B with DH and requirement for visual reference. On previous type we only had 2 autopilots so could only do approaches with 50ft DH/150m RVR. On both 744 and previous type in the fail passive (2 autopilot case) the aircraft trimmed back to allow safe GA in event of a (further) failiure.