Learn how aircraft brakes use hydraulic pressure and disc packs, when pilots apply them, and how to avoid skids, overheating and brake failure.
In real-world aviation, aircraft wheel brakes usually use hydraulic pressure to squeeze friction surfaces together, converting the aircraft's motion into heat. Pilots use them for taxi control, stopping after landing, rejected take-offs and parking, while avoiding prolonged or unnecessary application that can skid tyres or overheat the brakes.
How aircraft wheel brakes produce stopping force
Most aircraft have disc brakes on the main wheels, while the nose wheel is normally unbraked. A light aircraft may use a single disc and calliper; a transport aircraft typically has a multi-disc brake pack with alternating rotating and stationary discs.
Pressing the toe brakes, heel brakes or brake lever sends pressure to the callipers or brake pistons. The resulting friction slows the wheel, and tyre-to-runway friction slows the aircraft. Our overview of how brakes fit into the landing-gear assembly explains the wider wheel, tyre and retraction arrangement.
On many light aircraft, master cylinders connected to the rudder pedals generate the pressure directly. Larger aircraft generally receive pressure from the main hydraulic system, with an accumulator or separate alternate source available for failures. See our explanation of pumps, accumulators and hydraulic backup systems for that side of the process.
Left and right braking can be controlled separately. This differential braking helps turn an aircraft at low taxi speeds, especially when nose-wheel steering is limited, but excessive differential pressure can produce an abrupt swing or scrub a tyre.
When should pilots use aircraft brakes?
Pilots use wheel brakes mainly on the ground and only as much as the aircraft, runway and procedure require.
- Starting and parking: Use the parking brake to prevent movement while starting engines or completing checks, provided the aircraft procedure permits it. Chocks remain the safer long-term restraint because trapped hydraulic pressure can bleed away.
- Taxiing: Check brake response soon after the aircraft begins moving. Control speed with low power and smooth, intermittent applications rather than continuously riding the brakes against engine thrust.
- Turning: Apply differential braking when steering alone cannot make the required turn. Keep the speed low and release the brake as the turn develops.
- Run-up or holding position: Use the braking method specified by the aircraft checklist. Do not assume the parking brake alone can hold every aircraft at high power.
- Rejected take-off: Apply the braking called for by the rejected-take-off procedure. Transport aircraft may provide an RTO autobrake mode designed to command strong braking after a high-power abort.
- Landing: Apply manual braking after the main wheels are on the runway and the aircraft's procedure permits it. For maximum stopping with working anti-skid, firm continuous pressure is generally preferable to pumping the pedals.
- After stopping: Set the parking brake only when appropriate. After a high-energy stop or with indicated hot brakes, procedures may require chocks and brake cooling instead.
Aerodynamic drag, spoilers, propeller reverse or reverse thrust can reduce the energy that the wheel brakes must absorb. They assist braking but do not replace the wheel brakes or compensate for poor runway traction.
How are anti-skid, autobrake and parking brakes different?
These systems operate the same wheel brakes but control or retain brake pressure in different ways.
| System | What it does | Typical use |
|---|---|---|
| Manual brakes | Translate pedal or lever input into brake pressure | Taxiing, landing and normal stopping |
| Anti-skid | Reduces pressure at a wheel approaching a skid, then reapplies it as traction returns | Heavy braking and slippery runways |
| Autobrake | Automatically regulates braking to achieve a selected deceleration or rejected-take-off response | Airliner landings and take-off rejection |
| Parking brake | Usually traps hydraulic pressure or mechanically holds the brakes | Keeping a stationary aircraft from rolling |
| Alternate or emergency brake | Uses a separate pressure source, accumulator or control path | Loss of the normal braking system |
Anti-skid cannot create grip on standing water, ice or contamination; it can only use the traction available. Pilots should not pump brakes equipped with operating anti-skid because the system already performs the required pressure modulation. Our detailed guide to wheel-speed sensing and skid protection covers its limitations.
Autobrake is a control system, not a separate set of brakes. On many airliners it targets a deceleration rate, so using reverse thrust may cause the system to reduce wheel-brake pressure while maintaining the selected rate. Manual pedal input usually disarms or overrides it, although the exact logic varies; our airliner autobrake operating guide explains the common landing and RTO modes.
Should aircraft brakes be used in flight?
Wheel brakes normally provide no useful deceleration while airborne because the tyres are not touching a surface. Applying and holding them before landing can cause a locked wheel to contact the runway, risking a skid or tyre damage on aircraft without touchdown protection.
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 retraction, but pilots should do this only when the approved flight manual specifies it.
Why do aircraft brakes overheat or become ineffective?
Brakes overheat when they absorb energy faster than they can release it, especially after a high-speed rejected take-off, heavy landing, repeated short taxi movements or prolonged braking against power. The energy rises sharply with speed, so one high-speed stop can be far more demanding than several slow ones.
Excess heat can cause brake fade, damaged seals, tyre deflation through fusible plugs or, in severe cases, fire. Crews use brake-temperature indications, cooling times and brake-energy limits where fitted or published. A parking brake may be prohibited while the assemblies are very hot because it keeps pressure applied and can hinder cooling.
What should a pilot do if braking is weak or asymmetric?
Weak, dragging or one-sided braking requires the aircraft's abnormal checklist rather than improvised pedal pumping. Maintain directional control, reduce speed using the available aerodynamic devices and approved braking source, and use the alternate or emergency system only as directed.
A parking brake is not automatically an emergency brake, and pumping the pedals can deplete an accumulator on some aircraft even though it may restore pressure on others. If a wheel is locked, reducing brake pressure may allow it to rotate and regain directional grip. The aircraft flight manual and operator procedure always take precedence because brake-system layouts differ substantially.