Plain English Meaning
A type of instrument approach used in the very worst visibility, where the airplane and its automatic systems do most of the landing because the pilot may not be able to see the runway until the aircraft is on the ground — or, in some cases, not at all.
Full Definition
Category III (CAT III) approaches are precision instrument approaches conducted to runways equipped with an Instrument Landing System (ILS) certified for the lowest landing minimums. They allow operations in conditions where the (RVR) is below the limits of and , and in some cases permit landings with no and no requirement for the pilot to see the before . CAT III is divided into three subcategories — , , and — based on RVR and decision height limits, with IIIc allowing operations down to zero visibility. CAT III operations require specially certified aircraft, or fail- , crews, and an ILS facility with the appropriate ground equipment and lighting.