How do aircraft brakes work, and when should you use them?

Aircraft brakes usually use hydraulic pressure to clamp discs on the main wheels, converting motion into heat; a few designs use mechanical or electrically actuated brakes. Pilots use them for taxi control, landing, rejected take-offs and parking. Anti-skid helps prevent wheel lock, while differential braking helps turn the aircraft at low speed.

For our Aviation & Real-World Flying section, “aircraft brakes” means the wheel brakes used on the ground. Speed brakes, spoilers, aerodynamic drag and reverse thrust can assist deceleration, but they work differently and do not replace the wheel brakes.

How do airplane brakes work?

Airplane wheel brakes slow the rotating main wheels, and friction between the tyres and runway then slows the aircraft.

On a light aircraft, brake pads in a calliper usually squeeze a disc attached to the wheel. A transport aircraft commonly has a multi-disc brake pack: rotating discs are connected to the wheel, stationary discs are connected to a torque tube, and hydraulic pistons compress the entire stack. Steel and carbon brake packs have different weight, wear and temperature characteristics, but use the same friction principle.

The resulting kinetic energy becomes heat. The relationship E = ½mv² explains why speed matters so much: for the same aircraft mass, doubling the ground speed gives the brakes four times as much kinetic energy to absorb, before allowing for aerodynamic drag or reverse thrust.

Brakes are normally fitted to the main landing-gear wheels because they carry most of the aircraft's weight on the ground. The nose wheel is usually unbraked, although exceptions exist. During landing, spoilers improve wheel braking by reducing lift and placing more weight on the tyres.

Where does the brake pressure come from?

Most aircraft brakes are hydraulically operated, but the source and backup arrangements vary considerably.

Simple aircraft may have master cylinders connected directly to toe brakes, heel brakes or a hand lever. Larger aircraft generally use one or more powered hydraulic systems, often with an accumulator or alternate pressure source for abnormal operation. Our explanation of hydraulic pumps, accumulators and backup pressure covers how that power reaches systems such as the wheel brakes.

Some basic aircraft use mechanically operated cable brakes. Electrically actuated brakes are also fitted to certain modern aircraft; electric motors move the brake actuators, but friction in the disc pack still produces the stopping force.

What is differential braking in aircraft?

Differential braking means applying more brake pressure to one main wheel than the other so that the aircraft yaws towards the braked side.

With separate toe brakes, pressing the top of the left rudder pedal applies the left brake and pressing the right applies the right brake. Other aircraft distribute braking through a hand control, sometimes in combination with rudder-pedal position. The exact control arrangement must be learned for the individual type.

Differential braking is most useful during slow taxiing, particularly on aircraft with a free-castering nose wheel, limited nose-wheel steering or tailwheel landing gear. Keep the speed low and release pressure as the turn develops. Excessive application can lock a wheel, scrub a tyre or produce a sharp swing; it is not a substitute for proper high-speed directional control during take-off or landing.

For control-specific examples and common simulator assignments, see our detailed explanation of left and right differential braking.

When should pilots use aircraft brakes?

Pilots use wheel brakes only on the ground and only as much as the aircraft procedure, surface and stopping requirement demand.

• Before taxi: Release the parking brake, begin rolling slowly and make an early brake check. Confirm that both sides respond normally before reaching a congested area or significant slope.
• During taxi: Use low power and smooth, brief brake applications to control speed. A mistake we see constantly in simulation is carrying excessive thrust and riding the brakes continuously; the same technique wastes fuel and generates unnecessary heat in a real aircraft.
• For tight turns: Add differential braking only when rudder or nose-wheel steering is insufficient. Slow down before applying it.
• During run-up or while holding: Use the method specified by the aircraft checklist. Do not assume a parking brake can hold every aircraft against high engine power.
• For a rejected take-off: Follow the type-specific rejected-take-off procedure. Transport aircraft may have an RTO autobrake mode that commands strong braking when its arming and activation conditions are satisfied.
• After landing: Use manual brakes or the selected autobrake setting once the aircraft is on its wheels and the procedure permits braking.
• For parking: Set the parking brake when required for short-term restraint. Use chocks for longer parking because trapped hydraulic pressure can bleed away, and avoid setting hot brakes when the aircraft procedure prohibits it.

How should wheel brakes be used after landing?

After landing, wheel braking should be coordinated with spoilers, aerodynamic control and any approved reverse thrust rather than treated as an isolated action.

1. Establish weight on the wheels. Do not land with the brakes held unless the aircraft's approved procedure specifically calls for it. A locked tyre touching down can skid immediately.
2. Deploy or confirm lift-dumping devices. Spoilers reduce lift and increase the normal force on the tyres, allowing the brakes to use more of the available runway grip.
3. Use reverse where approved. Reverse thrust or propeller reverse reduces the energy left for the wheel brakes, particularly at higher speeds, but becomes less effective as speed falls.
4. Apply the required braking. With functioning anti-skid, use smooth, continuous pressure rather than pumping the pedals. Without anti-skid, pressure must be modulated to avoid locking a wheel.
5. Maintain directional control. Use rudder and nose-wheel steering as appropriate. Large differential brake inputs during a fast rollout can create a more serious directional problem.
6. Reduce braking before the turn-off. Slow to a safe taxi speed before leaving the runway rather than trying to make the exit with an abrupt turn and heavy one-sided braking.

Our practical guide to controlling the landing rollout explains how these controls are coordinated from touchdown to the runway exit.

How are anti-skid, autobrake and parking brakes different?

These systems use or control the wheel brakes in different ways; they are not separate aerodynamic braking devices.

Anti-skid monitors wheel behaviour and momentarily reduces pressure before a tyre remains locked. Many installations also include touchdown and locked-wheel protection, although operating thresholds and low-speed behaviour vary. Pumping the pedals interferes with a functioning anti-skid system and is normally the wrong technique.

Autobrake is a controller, not another set of brakes. On many airliners it targets a deceleration rate, so reverse thrust may cause the system to command less wheel-brake pressure while maintaining that rate. Manual pedal input commonly overrides or disarms autobrake, but pilots must use the logic published for their aircraft.

Should aircraft brakes be used in flight?

Wheel brakes provide no useful deceleration while the aircraft is airborne because the tyres are not in contact with the ground.

Holding the brakes before touchdown can make a wheel contact the runway while locked, risking a skid, flat-spotted tyre or loss of directional control. Touchdown protection on some anti-skid systems reduces that risk but is not a reason to land with brake pressure applied.

Some retractable-gear aircraft stop wheel rotation automatically during retraction. A few light-aircraft procedures call for a brief pedal application after take-off to stop spinning wheels before they enter the wheel well. That action should be taken only when the approved flight manual specifies it.

Why do aircraft brakes overheat or lose effectiveness?

Aircraft brakes overheat when they absorb energy faster than it can be released to the surrounding air.

Common causes include a high-speed rejected take-off, a heavy landing, repeated stop-start taxiing, holding the aircraft with brakes against high thrust and dragging a brake because of a control or hydraulic fault. Brake fade can then reduce friction or available pressure just when more stopping force is needed.

Severe heat may damage tyres, seals and hydraulic components. Fusible plugs fitted to some wheel assemblies can allow a controlled tyre deflation before pressure rises further, but hot brakes can still lead to fire or wheel failure. Crews use published brake-energy limits, temperature indications and cooling times where provided.

After a high-energy stop, the correct action comes from the aircraft checklist. That may include clearing the runway, avoiding the parking brake, using chocks and allowing a specified cooling period before another take-off.

What causes weak, dragging or asymmetric brakes?

Weak or one-sided braking can result from lost pressure, overheated brakes, a locked wheel, contamination, uneven brake wear or a fault in the normal or anti-skid system.

• Weak braking on both sides: Check hydraulic and brake indications and use the approved alternate system if directed. Repeated pedal pumping can deplete an accumulator on some aircraft, even though it may build pressure in other designs.
• Aircraft pulls to one side: One brake may be applying more strongly, the opposite brake may have failed, or one tyre may be skidding. Reduce excessive brake pressure enough to recover tyre rotation and use the abnormal checklist.
• A brake drags during taxi: Stop rather than adding power to overcome it. Residual pressure, a sticking brake, an incorrectly set parking brake or a mechanical fault can produce rapid heating.
• Parking brake will not hold: Use chocks or another approved restraint. A parking brake is not automatically an emergency braking system and should not be treated as one.

How should aircraft brakes be set up in a flight simulator?

In a flight simulator, separate analogue left and right brake axes give the most realistic control; buttons and keyboard inputs often behave as full-on or full-off commands.

1. Confirm the aircraft is ready to brake. Release chocks and the parking brake as appropriate, and make sure the simulated hydraulic or electrical brake source is available.
2. Inspect every brake assignment. Search the simulator's control bindings for brake commands and remove duplicates across pedals, joystick, controller and keyboard. A hidden duplicate can hold one brake on continuously.
3. Check axis direction and calibration. With the pedals released, both brake inputs should read zero or near zero. Reverse an inverted axis and add a small dead zone if noisy hardware applies residual braking.
4. Test left and right independently. Taxi slowly and confirm that each pedal turns the aircraft towards the corresponding side. If both pedals act together, they may be assigned to a combined brake command.
5. Compare with a default aircraft. If the controls work there but not in one add-on, the add-on may model hydraulic power, failures, chocks or custom brake logic that the default aircraft ignores.

If one particular aircraft still will not stop, use our systematic checks for an add-on whose brakes do not respond. With working anti-skid, hold a smooth braking command; without it, a progressive axis is far easier to control than repeatedly tapping a binary brake key.