Why does an aircraft drift off course during autoland?
Why does an aircraft drift off course during autoland? Diagnose crosswind crab, ILS setup errors, signal faults, scenery conflicts and rollout issues.
An aircraft can drift off course during autoland when the autopilot receives misleading ILS guidance, captures it badly, lacks enough control authority, or is incorrectly configured. In a crosswind, however, a nose pointed into wind is usually a normal crab: if the localiser remains centred, the aircraft is tracking the correct course.
This Aviation & Real-World Flying answer uses drift to mean the ground track moving away from the intended lateral path. The direction in which the nose points is the aircraft's heading; it need not match that ground track.
Can a plane drift during autoland?
Yes, an aircraft can genuinely drift sideways during autoland, but a crabbed heading is not proof that it has done so.
- Normal crab: the nose points into wind, the localiser remains centred and the aircraft continues towards the runway centreline.
- True aircraft drift: localiser deviation increases and the runway moves progressively towards one side of the windscreen.
- Guidance or scenery offset: the localiser remains centred, but the aircraft tracks consistently beside the painted centreline.
Watch the raw localiser deviation, flight-mode annunciator and ground track together. An exterior view can help diagnose a simulator problem, but nose alignment alone cannot tell you whether the plane is drifting.
What about crosswind during autoland?
A crosswind normally changes the aircraft's heading more than its track because the autopilot crabs into wind to remain on the localiser.
The wind does not move a correctly aligned localiser beam. Strong or gusty crosswinds can still cause genuine deviation if the autopilot reaches its control limits, repeatedly over-corrects or encounters rapid changes in wind near the ground. Automatic-landing wind limits are aircraft- and operator-specific; a crosswind permitted for a manual landing is not necessarily permitted for autoland.
During the flare, some aircraft apply a de-crab or runway-alignment command, while others retain part of the crab. The exact behaviour depends on the aircraft and its simulated systems. After touchdown, rollout guidance must counter crosswind and weathervaning; without it, the pilot must take over and use rudder or nose-wheel steering as appropriate. Our guide to controlling the centreline during landing rollout covers that separate phase.
Common causes of genuine aircraft drift
True autoland drift usually traces to the approach setup, localiser reception, capture geometry, aircraft configuration or runway data.
| What you observe | Likely cause | What to check |
|---|---|---|
| The aircraft overshoots and oscillates around the localiser | Late capture, excessive intercept angle, excessive speed, gusts or controller input | Intercept geometry, stabilisation, speed and hardware axes |
| The aircraft turns away when approach mode captures | Wrong runway, reciprocal course, navigation source or localiser | Approach selection, frequency, identifier, inbound course and source |
| The localiser remains centred but the runway is visibly offset | Offset localiser or mismatch between airport scenery and navigation data | Published approach alignment, scenery packages and runway position |
| The localiser suddenly moves close to the runway | Signal reflection, an aircraft or vehicle near the antenna, or disturbed reception | Raw deviation, ILS warnings and whether protected areas are active |
| Autoland status disappears or downgrades | Missing autopilot channel, invalid configuration or system failure | Flight-mode annunciations and the aircraft's autoland procedure |
| The aircraft departs the centreline only after touchdown | Rollout mode absent, disengaged or overridden | Rollout annunciation, rudder axis noise, crosswind and runway condition |
Autoland follows the ILS beam, not the painted line
An engaged autoland can steer accurately along wrong or distorted guidance because engagement does not validate the ILS signal or airport geometry.
A localiser defines an angular radio path. It cannot see the runway markings. Terrain, buildings, snow, airport works and nearby aircraft or vehicles can reflect or disturb that signal. During qualifying low-visibility operations, sensitive areas around the ILS equipment are protected; a practice autoland without those protections may be exposed to traffic-induced signal movement.
Some approaches also use a deliberately offset localiser rather than one aligned with the runway centreline. Such an approach may be suitable for instrument guidance but not for autoland. In a simulator, an older add-on airport can place the runway somewhere different from the navigation database's ILS position, producing a perfectly centred indication beside the visible runway.
Another mistake we see constantly is assuming that an armed APP indication proves the approach is correct. Approach mode merely tells the autoflight system to capture the selected guidance when its conditions are met. Our explanation of what APR or APP mode captures—and what it does not guarantee helps distinguish arming, capture and actual autoland capability.
How do I fix autoland drift in a flight simulator?
Fix simulator autoland drift by first deciding whether the fault follows the approach, the airport, the aircraft or an external control input.
- Distinguish crab from drift. If the localiser stays centred while the nose points into wind, the system is probably working normally. If the deviation grows, continue with the checks below.
- Confirm that the approach supports autoland. Use a suitable straight-in ILS and an aircraft model that implements automatic landing. An RNAV, visual, localiser-only or offset-localiser approach does not become an autoland because
APPis selected. - Verify the runway and ILS. Check the frequency, Morse identifier, front course and selected runway. Use these frequency, identifier and runway-selection checks if the aircraft captures an unexpected signal. Where the aircraft auto-tunes the ILS, verify what it selected rather than overriding it without reason.
- Select the correct navigation source. Conventional panels may require
NAVorVLOCinstead of GPS before localiser capture. Modern airliners may manage this automatically, so follow the modelled aircraft's procedure. See our explanation of when to use GPS versus NAV/VLOC on an ILS. - Set up a stable intercept. Join from a modest intercept angle, at a sensible speed and from below the glideslope. A fast or late intercept can overshoot the localiser, and each correction becomes more pronounced as localiser sensitivity increases near the runway.
- Read the flight-mode annunciator. Confirm that the localiser and glideslope are captured rather than merely armed. Then verify the required landing, flare and rollout status for that aircraft. Mode names and required autopilot channels differ between types.
- Check the selected course. The course selector does not rotate a real ILS beam, but an incorrect inbound course can confuse displays or guidance logic in some simulated aircraft. A reciprocal runway course is a common reason for misleading indications.
- Remove weather and control variables. Repeat the approach in calm conditions with failures cleared. Check for a noisy rudder, tiller, aileron or yaw axis, and make sure another controller or assistance feature is not adding input.
- Isolate the aircraft from the airport. Fly the same aircraft to another known straight-in ILS, then test another autoland-capable aircraft at the original runway. If the fault follows the aircraft, suspect its setup, systems modelling or controls. If several aircraft miss the same runway in the same way, suspect the airport or navigation data.
- Check scenery conflicts after updates. Disable duplicate or older airport packages and repeat the test. A simulator, navigation-data or airport update can expose a mismatch between the ILS position and an add-on runway even when both previously appeared usable.
When should pilots abandon an autoland?
Pilots should discontinue an autoland when the localiser becomes unstable, required landing status is lost, an ILS warning appears or the approach exceeds the applicable stabilisation and autoland limits.
The correct response depends on the aircraft, failure, height, visibility and operator procedure. A manual landing may remain permissible when the runway is visible and the aircraft is stable; otherwise the safe response is a go-around. In a simulator, applying the same discipline is more useful than trying to rescue an aircraft that is already diverging close to the ground.