Autoland

They may also include automatic braking to a full stop once the aircraft is on the ground, in conjunction with the autobrake system, and sometimes auto deployment of spoilers and thrust reversers.

Airports troubled by fog on a regular basis are prime candidates for Category III approaches, and including autoland capability on jet airliners helps reduce the likelihood that they will be forced to divert by bad weather.

[5][6] Commercial aviation autoland was initially developed in the United Kingdom, as a result of the frequent occurrence of very low visibility conditions in winter in North-west Europe.

The severity of this type of fog was exacerbated in the late 1940s and 1950s by the prevalence of carbon and other smoke particles in the air from coal burning heating and power generation.

Visibility at these times could become as low as a few feet (hence the London fogs of movie fame) and when combined with the soot created lethal long-persistence smog.

The basic concept of a "target level of safety" (10^-7) and of the analysis of "fault trees" to determine probability of failure events stemmed from about this period.

Similarly, it requires a crew trained in all aspects of the operation to recognize potential failures in both airborne and ground equipment, and to react appropriately, to be able to use the system in the circumstances from which it is intended.

The lateral guidance from the ILS localizer would however be usable right to the end of the landing roll, and hence is used to feed the rudder channel of the autopilot after touchdown.

As aircraft approached the transmitter its speed is obviously reducing and rudder effectiveness diminishes, compensating to some extent for the increased sensitivity of the transmitted signal.

The first "commercial development" automatic landings (as opposed to pure experimentation) were achieved through realizing that the vertical and lateral paths had different rules.

The pitch change occurs over the runway in the 1000 horizontal feet between the threshold and the glide slope antenna, and so can be accurately triggered by radio altimeter.

Autoland was first developed in BLEU and RAF aircraft such as the English Electric Canberra, Vickers Varsity and Avro Vulcan, and later for BEA's Trident fleet, which entered service in the early 1960s.

However, this triple-voting system is by no means the only way to achieve adequate redundancy and reliability, and in fact soon after BEA and de Havilland had decided to go down that route, a parallel trial was set up using a "dual-dual" concept, chosen by BOAC and Vickers for the VC10 4-engined long range aircraft.

In these operations the pilot had acquired full visual reference, normally well above decision height, but instead of fully disengaging the autopilot with the thumb-button, called for the second officer to latch off the roll channel only.

Having proven the reliability and accuracy of the autopilot's ability to safely flare the aircraft, the next elements were to add in similar control of the thrust.

Subsequently, autoland systems became available on a number of aircraft types but the primary customers were those mainly European airlines whose networks were severely affected by radiation fog.

The provision of the necessary ground equipment (ILS) and associated systems for Category 3 operations was almost non existent and the major manufacturers did not regard it as a basic necessity for new aircraft.

In general, during the 1970s and 1980s, it was available if a customer wanted it, but at such a high price (due to being a reduced production run item) that few airlines could see a cost justification for it.

This led to the absurd situation for British Airways that as the launch customer for the Boeing 757 to replace the Trident, the brand-new "advanced" aircraft had inferior all weather operations capability compared to the fleet being broken up for scrap.

An indication of this philosophical divide is the comment from a senior Boeing vice president that he could not understand why British Airways were so concerned about the Category 3 certification, as there were only at that time two or three suitable runways in North America on which it could be fully used.

At the same time, it became evident that the requirement for a true zero-visibility operation (as originally envisaged in the ICAO Category definitions) had diminished, as clean-air laws had reduced the adverse effect of smoke adding to radiation fog in the worst affected areas.

A major problem with this approach was that European authorities were very reluctant to certificate such schemes as they undermined the well-proven concepts of "pure" autoland systems.

This impasse was broken when British Airways became involved as a potential customer for Bombardier's Regional Jet, which could not accommodate a full Cat 3 autoland system, but would be required to operate in those conditions.

The feature is activated by a guarded red button on Garmin G3000 avionics, evaluating winds, weather and fuel reserves to select a suitable diversion airport and taking over the aircraft controls to land, it advises ATC and displays instructions to occupants.

[7] A Piper M600 single-engine turboprop aircraft began flight tests in early 2018 and completed more than 170 landings to seek pending FAA certification, which it achieved in 2020.

[7] In June 2021, the Garmin Autoland system won the 2020 Collier Trophy, for "the greatest achievement in aeronautics or astronautics in America" during the preceding year.

At the appropriate height above the ground (as indicated by the radio altimeter) the flight control computer will retard the throttles and initiate a pitch-up maneuver.

When the pilot arms the system (prior to capture of either the localizer or glideslope) the flight control computers perform an extensive series of built-in tests.

At this point the autoland mode will change to CAT III and the aircraft will be flown by the flight control computer along the localizer and glideslope beams.

At a predefined distance above the ground the aircraft will initiate the flare maneuver, maintain the same heading, and settle onto the runway within the designated touch down zone.