The system of the Airbus A320 is engineered around redundancy and safety, using several braking modes to stop the aircraft quickly and safely in all operating conditions. The A320 is equipped with carbon multi-disc brakes on the main landing gear (MLG), designed to offer strong braking performance, reduced weight, and excellent heat resistance. These carbon brake assemblies work with hydraulic and electronic control units to ensure a smooth, predictable deceleration rate during landing, rollout, and emergency braking.
The aircraft uses four braking modes—normal braking, alternate braking, accumulator backup, and the parking brake. Each mode ties into the Green and Yellow hydraulic systems, ensuring reliable braking even if hydraulic pressure or electronic control is degraded. This design helps the aircraft decelerate effectively on short runways, manage workload for pilots, and stop safely even in abnormal conditions.
Overview: Airbus A320 Brake System Architecture
The brake system integrates:
- BSCU for antiskid, autobrake, logic switching, and brake pedal interpretation.
- Green hydraulic system for primary braking in normal mode.
- Yellow hydraulic system for alternate braking and the parking brake.
- Carbon brakes with proven thermal stability and low wear rate.
- Brake cooling fans to manage heat buildup and reduce the risk of tire bursts.
- Hydraulic fluid pressure from either system or the accumulator for backup braking.
- Brake pedals sending electrical metering signals via the BSCU in normal and alternate modes.
This system of the Airbus A320 system ensures efficient braking control under a wide range of conditions. In failure cases, the system activates automatically to an alternate mode that still allows the aircraft to stop safely. These are key safety features that allow the aircraft to maintain performance even in degraded hydraulic and electronic configurations.
Normal Braking Mode (Green Hydraulic System)
Normal braking is active when Green hydraulic pressure is available and the A/SKID & N/W STRG switch is ON. In this mode, the BSCU meters brake force electronically as the pilot applies the brake pedals. Autobrake and antiskid are both available, and this combination helps prevent wheel lockup and potential tire bursts while providing strong, predictable deceleration appropriate for the available runway length.
A key point for pilots: In normal braking, there is no brake pressure indication on the triple pressure gauge; braking is fully managed through the BSCU and Green hydraulic system.
During rollout, pilots may also use thrust reversers with the thrust levers at idle or reverse. Thrust reversers reduce the load on the carbon brakes and help maintain directional control, especially in crosswind or contaminated conditions. At the same time, spoiler extension automatically increases weight on wheels, improving the friction available to the brakes and helping to stop the aircraft quickly and safely.
Alternate Braking Mode (Yellow Hydraulic System)
Alternate Braking With Anti-Skid
If Green system pressure becomes insufficient, the system activates automatically to Yellow-system braking. In this configuration, the brakes are supplied by the Yellow hydraulic system, while antiskid remains controlled by the BSCU. Brake pressure is displayed on the triple gauge, giving the crew direct feedback on Yellow-system brake pressure and accumulator status.
Even in this mode, the A320 continues to use its carbon brakes to achieve an effective and stable deceleration rate. The combination of Yellow-system pressure and antiskid logic still provides efficient braking and helps the aircraft stop safely within certified distances.
Alternate Braking Without Anti-Skid
When electronic control or antiskid capability is lost (for example after switching A/SKID & N/W STRG to OFF during a [LOSS OF BRAKING] procedure), the aircraft enters alternate braking without antiskid. In this mode, both antiskid and autobrake are inoperative, and brake pressure is automatically limited to approximately 1,000 psi to reduce the risk of wheel lockup and tire bursts.
Pilots must modulate the brakes carefully, especially on wet or contaminated runways, because neither skid protection nor autobrake supports them. Nevertheless, this degraded mode still allows the aircraft to stop the aircraft in a controlled way if the crew applies appropriate braking technique.
Accumulator Braking (Emergency Backup)
If both Green and Yellow hydraulic sources are unavailable, braking relies on the Yellow-system accumulator. This accumulator backup can provide at least seven full brake applications. Brake pressure is supplied solely by stored hydraulic fluid energy in the accumulator.
- Antiskid is not available.
- Nosewheel steering is lost; only rudder and differential braking remain for directional control.
- Pilots must limit brake pressure and avoid pumping the brakes to conserve accumulator energy.
Even with these limitations, the accumulator mode gives crews enough braking capability to stop the aircraft quickly and safely in an emergency braking scenario, provided the remaining runway and speed allow it.
Autobrake Function and Settings
The autobrake system provides preset deceleration rates during landing or during a rejected takeoff (RTO). This system reduces pilot workload and ensures consistent, symmetrical brake application—ideal for contaminated or short runways where runway margins are reduced.
For RTO, MAX autobrake arms before takeoff and becomes active only if:
- The aircraft is above approximately 72 kt wheel speed.
- Thrust is reduced from takeoff power (thrust levers at idle or reverse).
- Ground spoilers deploy, confirming that the aircraft is on the ground.
Autobrake Modes
Anti-Skid Protection and BSCU Logic
Anti-skid prevents wheel lockup by reducing brake pressure during impending skid conditions. It is one of the key safety features that ensure a smooth deceleration profile and reduce the risk of hydroplaning or tire bursts. The BSCU compares individual wheel speeds with a reference and meters pressure to each wheel to maintain optimal braking effectiveness.
Together, anti-skid and autobrake give the A320 a highly effective and predictable stopping capability, particularly valuable on contaminated surfaces and during high-energy RTOs.
Brake Cooling, Temperature, and Safety Features
The A320’s carbon brake assemblies generate significant heat during landing and RTO. Brake temperature is monitored via the WHEEL SD page. If temperatures rise above operational thresholds, brake cooling fans may be used to accelerate cooling and protect brake and tire integrity. Proper cooling also helps avoid thermal issues that could compromise future braking performance.
This thermal resilience is one reason carbon brakes are preferred across modern airliners: they handle high energy, cool relatively quickly, and support consistent stopping power over many cycles.
Parking Brake and Ground Safety
The parking brake uses Yellow system pressure or accumulator pressure and holds the aircraft securely during parking. The triple indicator must show adequate accumulator pressure in the green band before engine shutdown to ensure that the parking brake can maintain pressure, even after hydraulic pumps are off.
Brake application through the parking brake is smooth thanks to the carbon braking system design, and adequate accumulator charge ensures the aircraft can remain safely parked without continuous hydraulic power.
A320 Brake Mode Comparison
Brake Modes Overview
Closing Insight
With a combination of digital logic, hydraulic redundancy, and high-performance carbon brakes, the Airbus A320 braking ensures efficient stopping capability in both normal and abnormal scenarios. Even with degraded systems, pilots retain the ability to stop the aircraft quickly and safely, making these braking modes central to operational confidence and safe landing performance across the A320 fleet.