CAT III Landing

A CAT III landing is an instrument approach and landing conducted in extremely low visibility conditions using the aircraft's automated landing systems, the airport's Instrument Landing System (ILS), and highly precise navigation equipment, without the pilot needing to see the runway until the aircraft is very close to or already touching down. CAT III is the highest tier of the internationally standardized approach categories and represents the outer limit of human-automated system collaboration in commercial aviation.

What Is a CAT III Landing?

The International Civil Aviation Organization defines instrument approaches in three main categories based on the minimum visibility and cloud ceiling height (decision height) at which a pilot must be able to see the runway environment to continue the approach. CAT I requires a decision height of at least 200 feet and a runway visual range of at least 550 meters. CAT II drops the decision height to 100 feet and RVR to 350 meters. CAT III is subdivided into three subcategories: CAT IIIa allows a decision height as low as 100 feet and RVR as low as 200 meters. CAT IIIb permits decision heights below 50 feet (or no decision height at all) with RVR as low as 50 meters — conditions equivalent to dense fog where the runway is effectively invisible until the aircraft is nearly on it. CAT IIIc, theoretically zero/zero operations, is defined but not yet operationally approved at any airport.

How It Works in Practice

A CAT III approach requires three simultaneous elements to function correctly: a suitably equipped aircraft, a suitably equipped airport, and a suitably qualified crew. The aircraft must have a dual or triple redundant autopilot and flight director system certified for automatic landing (autoland), along with dual radio altimeters, fail-operational hydraulic systems, and CAT III-certified avionics. The airport must have a CAT III ILS installed with a localizer providing lateral guidance and a glide slope providing vertical guidance to published precision standards, supplemented by approach lighting systems visible from 50 to 200 meters. The crew must hold a CAT IIIb rating on their type certificate and conduct a minimum number of ILS approaches per 90-day period to remain current. During the approach, the autopilot flies the aircraft automatically; the crew monitors systems and is prepared to take over if a failure occurs. At airports like London Heathrow and Amsterdam Schiphol — notorious for winter fog — CAT III approaches are routine events handled dozens of times per day.

Why It Matters

CAT III capability is economically critical for airlines and airports operating in climates prone to fog, freezing fog, and low-stratus cloud. Without CAT III, a London winter fog that reduces visibility to 100 meters would ground an airport entirely. With it, operations continue — though at a reduced rate because spacing between aircraft must be increased and runway occupancy time carefully managed. The economic value of CAT III at major hubs runs to billions of dollars per year in preserved capacity. For passengers, CAT III means that a flight into Heathrow during a November pea-souper is far more likely to land than to divert.

Key Facts and Figures

• CAT IIIb is the most stringent approach category in routine commercial use, with RVR minimums as low as 75 meters at some airports.
• London Heathrow, Amsterdam Schiphol, Paris Charles de Gaulle, Frankfurt, and Chicago O'Hare are among the world's busiest CAT III-equipped airports.
• Aircraft certified for CAT III autoland include the Boeing 737, 747, 777, 787, and all Airbus A320/A330/A340/A350/A380 families.
• A CAT IIIb-certified aircraft must have a fail-operational autopilot: if one channel fails during the approach, the remaining channels continue to fly the aircraft to touchdown.
• Most major airlines require CAT III approaches to be conducted with the autopilot engaged until after touchdown and the rollout is stabilized.
• CAT III certification for an airline requires demonstrated competency in simulator training, with annual recurrency checks.

Related Concepts

Instrument Landing System, Autoland, Decision Height, Runway Visual Range, ATC