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Autoland describes a system that fully automates the landing phase of an aircraft's flight, with the human crew supervising the process. The pilots assume a monitoring role during the final stages of the approach and will only intervene in the event of a system failure or emergency and, after landing, to taxi the aircraft off of the runway and to the parking location.
Some autoland systems require the pilot to steer the aircraft during the rollout phase on the runway after landing, among them Boeing´s fail passive system on the BOEING 737-700 NG, as the autopilot is not connected to the rudder.
On the AIRBUS A-320 series and A330, 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 autobrake, a full stop can be made on the centre line without pilot intervention. If the NWS is not available, the QRH dictates that the autopilots must be disconnected immediately on touchdown and the pilot control the aircraft through the rollout.
Autoland systems were designed to make landing possible in meteorological conditions too poor to permit any form of visual landing, although they can be used at any level of visibility.
The Autoland System
The autoland system incorporates numerous aircraft components and systems such as the autopilot(s), autothrust, radio altimeters and nose wheel steering. Although not an integral component of the autoland system, the autobrake system is often used in conjunction with an automatic landing.
The pilots must program the FMS (or tune the appropriate radio aids), configure the aircraft for landing and engage the autopilot and autothrust systems in the normal fashion. The Autoland system then provide inputs to the aircraft flight controls and adjusts the engine power settings in order to maintain the required approach profile and land the aircraft safely without pilot intervention. Some systems require the pilot to reduce thrust to idle when performing autoland. The Airbus requires the pilot to move the thrust levers to the idle positon when the autocallout calls "RETARD" at 10' RA. HOWEVER, the autothrust has already reduced the thrust to idle before this point - the retard call is to remind the pilot to match the thrust levers to the demanded thrust requirement. In all cases, the pilot must select reverse thrust settings. The autopilots will be disengaged after landing to taxi clear of the runway.
The approach can always be discontinued at any time by pressing the TOGA switches or in the case of an Airbus, by advancing the thrust levers to TOGA detent. Depending on the aircraft type or autopilot system installed, the auto pilot may or may not disconnect at this point. Most aircraft capable of an autoland also have the capability of performing a go-around with the autopilot engaged.
Autoland systems are normally designated Fail Operational or Fail Passive.
- A Fail 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 fail passive system is normally 50’.
Suitability of Instrument Landing Systems
Depending on aircraft type and installed autopilot system, autoland may be used in any weather conditions at or above published minima on any runway with an ILS installed. Operators should note however that some CAT I installations are not suitable for autoland due to offset localizers or to unstable localizer or glideslope signals once below published minima. CAT II and CAT III installations should be used with caution when LVP are not in effect as the localizer or glideslope signals may be compromised by ground traffic. The aircraft AFM and company SOP should be consulted for further guidance.
The aircraft operator must be approved by the authority and pilots must be suitably qualified and experienced in accordance with IR-SPA.LVO.120 (Appendix 1 to EU OPS 1.450.)
Accidents and Incidents
Events in the SKYbrary database which include AP/FD and/or ATHR status awareness as a contributory factor:
- A320, vicinity Lyons Saint-Exupéry France, 2012 (On 11 April 2012, a Hermes Airlines A320 commanded by a Training Captain who was also in charge of Air Operations for the airline was supervising a trainee Captain on a night passenger flight. The aircraft failed to establish on the Lyons ILS and, in IMC, descended sufficiently to activate both MSAW and EGPWS 'PULL UP' warnings which eventually prompted recovery. The Investigation concluded that application of both normal and emergency procedures had been inadequate and had led to highly degraded situational awareness for both pilots. The context for this was assessed as poor operational management at the airline.)
- A332 MRTT, en-route, south eastern Black Sea, 2014 (On 9 February 2014, the Captain of a military variant of the Airbus A330 suddenly lost control during the cruise on a passenger flight. A violent, initially negative 'g', pitch down occurred which reached 15800 fpm as the speed rose to Mach 0.9. In the absence of any effective crew intervention, recovery was achieved entirely by the aircraft Flight Envelope Protection System. The Investigation found that the upset had occurred when the Captain moved his seat forward causing its left arm rest to contact the personal camera he had placed behind the sidestick, forcing the latter fully forward.)
- A343, en-route, mid North Atlantic Ocean, 2011 (On 22 July 2011 an Air France A340-300 en route over the North Atlantic at FL350 in night IMC encountered moderate turbulence following "inappropriate use of the weather radar" which led to an overspeed annunciation followed by the aircraft abruptly pitching up and gaining over 3000 feet in less than a minute before control was regained and it was returned to the cleared level. There Investigation concluded that "the incident was due to inadequate monitoring of the flight parameters, which led to the failure to notice AP disengagement and the level bust, following a reflex action on the controls.”)
- AT76, en route, west-southwest of Sydney Australia, 2014 (On 20 February 2014, an ATR 72-600 crew mishandled their response to an intended airspeed adjustment whilst using VS mode during descent to Sydney and an upset involving opposite control inputs from the pilots caused an elevator disconnect. The senior cabin attendant sustained serious injury. After recovery of control, the flight was completed without further event. Post flight inspection did not discover damage to the aircraft which exceeded limit and ultimate loads on the stabilisers and the aircraft remained in service for a further five days until it was grounded for replacement of both horizontal and vertical stabilisers.)
- B732, vicinity Resolute Bay Canada, 2011 (On 20 August 2011, a First Air Boeing 737-200 making an ILS approach to Resolute Bay struck a hill east of the designated landing runway in IMC and was destroyed. An off-track approach was attributed to the aircraft commander’s failure to recognise the effects of his inadvertent interference with the AP ILS capture mode and the subsequent loss of shared situational awareness on the flight deck. The approach was also continued when unstabilised and the Investigation concluded that the poor CRM and SOP compliance demonstrated on the accident flight were representative of a wider problem at the operator.)
- IR-OPS SPA.LVO.120 - Low visibility operations - Training and qualifications
- Acceptable Means of Compliance and Guidance Material to IR-OPS SPA.LVO.120
- EU-OPS 1.450, Appendix 1: Low visibility operations — Training and qualifications.
- Flight Safety Foundation ALAR Briefing Note 1.2 - Automation
- Airbus: "Getting to Grips with CATII and CATIII"