Aircraft Brake Systems: Auto-Brake, RTO, and Anti-Skid Logic

021-04-03Pablo Asensio Martínez2026-03-272 min

The brake system provides the means to stop the aircraft during landing and rejected take-off (RTO). Modern aircraft employ advanced systems like Anti-Skid and Auto-Brake to optimize braking performance and safety.

Auto-Brake System Operation

The auto-brake system assists pilots by automatically applying wheel brakes during landing and RTO.

  • Landing Mode:

    • Provides a predetermined, constant rate of deceleration (e.g., knots lost per second).
    • The system modulates brake pressure to achieve this target deceleration.
    • Effect of Reverse Thrust: If reverse thrust is used, it contributes to the deceleration. The auto-brake system compensates by reducing brake pressure to maintain the same total deceleration rate. This results in cooler brakes, but does not change the deceleration rate.
    • Weight independence: The constant deceleration target is maintained regardless of aircraft weight (assuming sufficient friction exists).

  • Rejected Take-Off (RTO) Mode:

    • Applies maximum brake pressure immediately when the system is triggered.
    • Unlike landing mode, it does not target a specific deceleration rate; it aims for maximum stopping power. The actual deceleration may vary due to runway conditions (e.g., slippery spots).
    • Performance vs. Manual Braking: RTO and maximum manual braking can achieve the same deceleration rate. However, RTO offers a safety benefit because it reacts immediately, whereas manual braking involves pilot reaction time, leading to a longer stopping distance.

  • Disarming Conditions: The auto-brake system will disarm immediately if:

    • The pilot applies manual braking.
    • Any thrust lever is advanced after landing.
    • The speed brake lever is moved to the DOWN detent.
    • The system is switched to OFF or DISARM.

Anti-Skid System

The anti-skid system determines if a wheel is about to lock up and reduces brake pressure to maintain tire rotation and maximum braking efficiency.

  • Interaction with Auto-Brake: The auto-brake system relies on the anti-skid system. If the anti-skid system is inoperative, the auto-brake system will not function.
  • Performance Impact: Failure of the anti-skid system increases the distance required to stop on both wet and dry runways.
  • In RTO Mode: While RTO commands maximum pressure, the anti-skid system may still modulate (reduce) this pressure to prevent wheel lock-up on slippery surfaces.