As you begin maneuvering for the planned approach, the controller states that, due to a marine layer that has moved into the area, visibility has gone from the forecast 2 mi. to less than a quarter of a mile. You’ve come prepared. Thanks to the special onboard systems, this approach is authorized down to zero/zero conditions. It is flown completely by the autopilot.
On final, the aircraft stabilizes, and with the autothrottles making minute adjustments, the approach continues. You hear, “Two hundred” as that radar altitude slips by. You know that this is the point where you would normally have had to see the approach lights, but you don’t. You continue. “One hundred.” Still there is nothing in view out the window. “Fifty” . . . nothing. “Forty” . . . nothing. “Thirty” . . . nothing. The autothrottles bring the engines to idle and you note the nose of the airplane rising as the autopilot commands a flare. The main gear kisses the concrete and as the nose lowers to the runway, you are just able to see the first couple of runway lights ahead of the airplane. Safely and right on time, you’ve arrived.
Welcome to 1972. The approach just described was “shootable” way back then in airplanes equipped with Category IIIC landing systems. Remember that CAT IIIA requires 700 RVR and CAT IIIB requires 150 RVR, but CAT IIIC has no visibility requirement.
If the technology existed more than 40 years ago, why aren’t all airplanes flying today able to make zero/zero approaches?