Learn how aircraft autoland uses ILS, redundant autopilots, radio altimeters and rollout guidance, plus the exact conditions required for use.
Aircraft autoland uses a certified automatic flight-control system to capture an instrument approach, hold the runway centreline and descent path, flare, touch down and usually steer during rollout. In real-world aviation, it may be used only when the aircraft, crew, approach, runway, weather and required ground equipment all meet their approved limits.
What happens during an automatic landing?
The system turns a precision approach into three controlled phases: guidance to the runway, automatic flare and touchdown, then centreline control during rollout.
- Arm a valid precision approach. Most conventional autoland systems use an ILS. Both localizer and glideslope guidance must be captured; understanding the difference between localizer-only guidance and a full ILS explains why lateral capture alone is insufficient. Selected approved aircraft and runways can use GLS, but an ordinary RNAV/GNSS approach or programmed FMS path does not provide autoland by itself.
- Engage the required redundancy. Depending on the aircraft, two or three autopilot channels may be required. Independent receivers, flight-control computers and radio altimeters monitor one another so that a fault can be detected without silently commanding a bad landing.
- Track and monitor the approach. The autopilot follows the localizer and glideslope while autothrust or autothrottle manages thrust according to the aircraft design. The flight mode annunciator must show the type-specific landing status; an illuminated
APPbutton does not prove that autoland is available. - Flare and touch down. At a design-specific radio altitude, the system changes from glideslope tracking to flare logic, reduces the descent rate and commands the required pitch. Thrust retard and de-crab behaviour vary by aircraft.
- Control the rollout. An approved rollout mode uses rudder and, where fitted, nosewheel steering to remain near the centreline. Spoilers and autobrakes are separately armed systems, while pilots normally select reverse thrust and take over steering at the prescribed point.
Autoland is a specialised part of the wider automatic flight-control system. Our explanation of how an aircraft autopilot controls pitch and roll covers the underlying servos, sensors and mode logic.
When can aircraft autoland be used?
Autoland can be used only when every operational layer supports it; having an autoland-capable aircraft is not enough.
| Area | What must be verified |
|---|---|
| Aircraft | The aircraft is approved for the intended operation, and all equipment required by its manuals and maintenance status is serviceable. |
| Crew and operator | The operator holds the necessary approval, and the pilots are trained, qualified and following the aircraft-specific procedure. |
| Approach and runway | A suitable published precision approach and runway are available, with no restriction or outage preventing the intended operation. |
| Ground facilities | The ILS or other approved landing system is operating correctly. For low-visibility operations, its critical and sensitive areas must be protected from aircraft and vehicles. |
| Weather and runway | RVR, wind, runway condition and braking action remain within the applicable aircraft, operator and airport limits. |
| Approach condition | The aircraft is stabilised, correctly configured and established within the permitted capture geometry, with no windshear warning or excessive guidance deviation. |
The controlling documents are the aircraft flight manual, operator procedures, minimum equipment provisions, approach chart and relevant operational notices. Autoland wind limits may be lower than the aircraft's manual-landing limits, particularly for crosswind or tailwind, so a generic maximum wind figure cannot be used.
Does autoland mean CAT III or zero visibility?
No. Autoland and CAT III are related, but they are not interchangeable terms.
CAT I, II and III describe progressively lower operating minima together with the required aircraft, crew, airport and approach capabilities. Our guide to CAT I, II and III operating minima explains the relationship between decision height, RVR and approval.
CAT III operations commonly use autoland because outside visual references may be insufficient for a manual landing, although some approved head-up guidance systems support low-visibility manual landings. Conversely, an operator may permit autoland on a suitable CAT I approach in good weather for practice or system checks.
A good-weather practice autoland still needs careful monitoring because CAT III ILS signal-protection procedures may not be active. A vehicle or another aircraft near the antenna can distort the beam close to touchdown. The phrase zero-zero landing is also misleading: even a no-decision-height approval normally retains operational requirements for RVR, runway protection, rollout and subsequent taxiing.
Fail-passive versus fail-operational autoland
These terms describe what the automatic landing system can do after a relevant single failure.
| Capability | Response to a failure | Practical consequence |
|---|---|---|
| Fail-passive | The failure causes no significant flight-path upset, but the automatic landing cannot necessarily be completed. | The pilot must take control or go around, subject to the height, visual references and approved procedure. |
| Fail-operational | Enough independent capability remains to continue the automatic approach, flare and landing after the specified failure. | It can support lower minima when the complete aircraft, crew and runway operation is approved. Rollout capability must also be checked. |
Annunciations such as LAND 2, LAND 3 or CAT 3 DUAL are aircraft-specific rather than universal. A status downgrade above the relevant alert height may require a go-around or higher minima; the aircraft procedure determines the response.
What does the pilot still have to do?
Pilots manage and continuously monitor an autoland; it is not an autonomous landing that removes them from the loop.
- Verify the correct approach, frequency, identifier, course and minima, including automatically tuned data.
- Configure the aircraft and engage the required autopilot, autothrust and landing systems in the proper sequence.
- Monitor the flight mode annunciator, raw localizer and glideslope data, speed, descent path and autoland status.
- Go around after an unstable approach, excessive deviation, disqualifying warning or capability loss when the procedure requires it.
- Apply reverse thrust where appropriate, monitor braking and rollout, then take over for runway exit and taxi.
Unnecessary control-column or sidestick pressure can disconnect or override automation on some aircraft. The crew must remain ready to intervene, but should not disturb a correctly functioning system without reason.
Why does autoland fail or disconnect?
An autoland usually fails because a required mode, redundant channel, signal or aircraft capability is missing.
- Approach mode is armed but not captured. Localizer capture without glideslope capture is still only lateral guidance.
- The intercept is unsuitable. Excessive height, a steep intercept angle or trying to capture a glideslope from above can prevent correct mode engagement or lead to false guidance.
- A required autopilot channel will not engage. This often indicates incorrect sequencing, incompatible configuration or an equipment fault.
- The ILS signal is disturbed. Terrain, buildings, taxiing aircraft and vehicles can bend or reflect the signal, especially when low-visibility protection is not active.
- The system downgrades. A radio-altimeter, receiver, flight-control computer or other monitored fault may remove fail-operational capability or autoland entirely.
- Operational limits are exceeded. Strong winds, poor braking, excessive deviation, turbulence, windshear or an unstable approach can require a manual landing or go-around.
In a flight simulator, the aircraft model itself must also implement automatic flare and rollout; some models only capture and fly the ILS approach. Scenery or navigation-data mismatches can offset the simulated localizer as well. A practical Boeing 737 simulator ILS setup and monitoring sequence shows the checks leading up to landing, but the chosen aircraft's documentation remains decisive.
A mistake we see frequently is treating a centred glideslope indicator as proof that autoland is active. It confirms vertical approach guidance, not the required redundancy, flare logic or rollout capability.