Regulatory approval for Autoland was first given in 1968 with the first CAT III landing taking place in Jan 1969 (Sud Aviation Caravelle).

 

Early adopters of Category III technology include The Hawker Siddeley HS Trident, Boeing B747-200, and Concorde. In 1974, the Airbus A300 was certified for Category III A, and in 1983 the Airbus A310 achieved certification followed by the Airbus A300-600 in 1984 which achieved CAT III B.

 

The fail-operational automatic landing was first used for these types of operations, but it was found useful to develop fail-passive capability to comply with operational requirements.

 

 

Autoland systems are normally designated Fail Operational or Fail Passive.

 

A failed operational system must have at least two autopilots engaged for the approach. The failure of one autopilot will still allow an autoland to be carried out. This allows a “no decision height” approach to be conducted.

 

A Fail Passive system is normally associated with a single autopilot approach. In this case, failure of the autopilot will not result in any immediate deviation from the desired flight path; however, the pilot flying must immediately assume control of the aircraft and, unless he has sufficient visual reference to land, carry out a missed approach.

 

The lowest allowable decision altitude (DA) for a failed passive system is normally 50’.

 

 

Whilst “Autoland Capability” equipment represents a significant cost for an airline. Diversions are extremely expensive for an airline with both direct and indirect costs as well as schedule disruptions. 

 

Applying for regulatory approval for CAT II and CAT III approaches may be considered a worthwhile step in the evolution of a modern airline.

 

Modes of Operation 

 

Low Visibility Operations include:

 

- Manual take-off with or without electronic guidance systems

- Auto-coupled approach to below DH, with manual flare, landing, and roll-out

- Auto-coupled approach followed by auto-flare, autolanding, and manual roll-out

- Auto-coupled approach followed by auto-flare, autolanding and auto-roll-out

 

An autopilot system with a rollout capability is one capable of guidance on the runway centreline.

 

 

The autoland system steers the aircraft on the runway, initially through the rudder and, as the aircraft slows via the nose wheel steering (NWS). In conjunction with the auto brake, a full stop can be made on the center line without pilot intervention.

 

Note - If the NWS is not available, the Quick Reference Handbook (QRH) dictates that the autopilots must be disconnected immediately on touchdown and the pilot controls the aircraft through the rollout.

 

 

We can break the landing limits down now into three categories i.e. CAT I, II, and III.

 

CAT I is a normal approach.

 

CAT II and III are low-visibility operations.

 

For both CAT II and CAT III operations, Decision Height (DH) is based on the radar altimeter.