How do airliner autobrakes work, and when should I use them?

An airliner autobrake system automatically meters wheel-brake pressure to achieve a selected deceleration after touchdown, or maximum braking during a rejected take-off. Use a landing level chosen from the aircraft’s performance calculation and operating procedures; arm RTO for take-off when required. Autobrake improves consistency, but it cannot create extra tyre grip.

For our Aviation & Real-World Flying readers, the key point is that autobrake is a deceleration controller, not a fixed-pressure brake setting. The names, activation conditions and available levels vary between aircraft, so the aircraft manual and operator procedures always take precedence.

How does an airliner autobrake system work?

An autobrake is a closed-loop system that compares the selected deceleration with the aircraft’s measured deceleration, then increases or reduces hydraulic brake pressure. Selecting a higher level requests stronger deceleration; it does not simply apply a fixed percentage of braking.

1. The crew selects and arms a mode. This may be a numbered landing level, LOW or MED, or an RTO mode for take-off.
2. Touchdown logic confirms that the aircraft is on the runway. Depending on the type, this can involve wheel spin-up, weight-on-wheels sensors, idle thrust levers and ground-spoiler deployment.
3. The controller commands brake pressure. It continually adjusts that pressure to maintain the selected deceleration as aerodynamic drag, reverse thrust and runway conditions change.
4. Anti-skid limits individual wheels. If a tyre approaches a skid, pressure is reduced at that wheel even when the autobrake is asking for more deceleration.

During a rejected take-off, RTO logic commands very strong braking when its activation conditions are met, normally after the take-off has passed an aircraft-specific speed or thrust threshold. A low-speed rejection may still require manual braking. We avoid quoting a universal trigger speed because it differs by aircraft.

Which autobrake setting should I use for landing?

Use the lowest setting that satisfies the approved landing-performance calculation, runway conditions and operating procedure. A long, dry runway may permit a low level; a short, wet or otherwise limiting runway usually requires a stronger selection.

Those labels are not equivalent between manufacturers. Boeing-style numbers are deceleration levels, not percentages, while common Airbus logic uses LOW and MED for normal landings and MAX primarily for rejected take-off protection.

Base the choice on runway length, reported braking action, wind, slope, landing weight, approach speed, expected touchdown point and any reverse-thrust assumptions in the performance calculation. A desired taxiway exit comes after stopping margin: never select weak braking merely to roll farther, or excessive braking solely to make an early exit.

What is the normal autobrake landing sequence?

A normal autobrake landing requires the mode to be selected, armed and then verified after touchdown.

1. Before landing, choose the level supported by the landing calculation and set the selector.
2. Arm the required systems, including the ground spoilers where the aircraft procedure calls for it, and confirm the cockpit’s armed indication.
3. After touchdown, confirm spoiler deployment, reverse thrust as required and the expected deceleration indication.
4. Monitor the rollout. Take over immediately if braking is weaker or stronger than expected, directional control is threatened, or an alert appears.
5. Approaching taxi speed, apply manual braking smoothly as required. On most airliners this cancels autobrake, after which the selector is returned to the prescribed position.

Does autobrake work with reverse thrust and anti-skid?

Autobrake, reverse thrust, spoilers and anti-skid perform different but complementary jobs. Ground spoilers remove lift and put more weight on the wheels, reverse thrust adds deceleration, autobrake regulates the wheel brakes, and anti-skid protects tyre grip. Our explanation of wheel brakes, anti-skid and weight-on-wheels logic covers the hardware beneath that sequence.

On systems that regulate measured aircraft deceleration, reverse thrust and aerodynamic drag reduce how much wheel-brake pressure is needed to reach the target. That can reduce brake heating, but reverse thrust does not make the selected autobrake level unnecessary. In Microsoft Flight Simulator, correct control assignments also matter; our reverse-thrust control guidance for MSFS explains the usual throttle and binding arrangements.

Autobrake is not a stopping-distance guarantee. A fast approach, long touchdown, tailwind or contaminated runway can consume the available margin before the system has any chance to help.

Do Airbus and Boeing autobrakes behave differently?

Yes; the underlying principle is similar, but the selectors, mode names, arming logic and indications differ. On an Airbus A320-family aircraft, a DECEL indication generally confirms that the required deceleration is being achieved—it does not prove that substantial wheel-brake pressure is being applied, because reverse thrust and drag may already be doing much of the work.

Boeing aircraft commonly use numbered landing levels alongside MAX and RTO positions, but the number of levels and their behaviour vary by model. For the Airbus layout, our guide to where the A320 braking controls and indications fit in the cockpit provides the surrounding control context.

Brake-to-vacate is a more advanced function than conventional autobrake. Instead of holding one deceleration level, it computes a braking profile for a selected runway exit; the practical differences are shown in our A380X brake-to-vacate procedure.

Why will the autobrake not arm or activate?

Most autobrake failures in a simulator come from an unmet activation condition or an unwanted manual-brake input rather than a defective braking system.

• No armed indication: check the selected mode, anti-skid state, hydraulic availability and any brake-system warning. Some modes can only be armed on the ground or in a particular aircraft configuration.
• Armed but no touchdown braking: verify idle thrust, ground-spoiler deployment and weight-on-wheels or wheel spin-up. A bounced landing can disturb this sequence, with behaviour varying by aircraft.
• Immediate disconnection: a noisy toe-brake axis may be sending a small continuous input. Add a modest dead zone, calibrate the pedals and remove duplicate brake assignments.
• Unexpectedly weak stopping: the chosen level may be low, anti-skid may be limiting pressure on a slippery runway, or touchdown may have occurred too far along the runway.
• Braking feels unrealistically abrupt: check that the simulator has not mapped a button directly to full brakes. Simplified aircraft may also model autobrake as preset pressure rather than true target deceleration.

When should I take over from autobrake?

Take over immediately whenever the achieved deceleration or directional control is not satisfactory. Use manual braking for an abnormal rollout, an autobrake fault, a required rapid stop beyond the selected mode’s capability, or a smooth transition while turning off the runway.

Manual pedal input normally overrides or disconnects autobrake, but the exact cancellation logic is aircraft-specific. Avoid resting your feet on sensitive toe brakes in a simulator: even a small input can cancel the system before it begins braking.