Anti-Skid Systems

Operating Principle

Modern anti-skid systems use electronic sensors to continuously compare each wheel's rotational speed with the aircraft's ground speed. The anti-skid computer calculates the slip ratio—the difference between the theoretical and actual wheel speed—to keep braking at the threshold of maximum friction without causing a skid. If a wheel decelerates too quickly (indicating an impending skid), the system automatically reduces brake pressure just enough to let the wheel regain speed, then reapplies pressure to maintain optimal braking.

Key Protections

• Slip Ratio Regulation: Ensures the best possible braking by keeping each wheel just short of skidding.
• Locked-Wheel Prevention: Stops any wheel from fully locking up, which would lead to loss of control and tyre damage.
• Touchdown and Bounce Protection: Prevents brake pressure from being applied before wheels are spinning at ground speed, avoiding flat spots and tyre bursts during landing and after any bounce.
• Hydroplane Protection: Detects excessive slip caused by water and reduces brake pressure to restore tyre contact with the runway.

System Performance and Failure

With anti-skid active, aircraft achieve shorter, safer stopping distances and improved directional control, especially on wet or contaminated runways. If the anti-skid system fails, landing distances can increase by up to 50%, and the risk of tyre damage or loss of control rises sharply. Pilots cannot match the precision of an anti-skid system through manual braking alone.

Autobrake Integration

Autobrake systems depend on anti-skid to function safely. Without anti-skid, autobrake cannot regulate slip ratio or prevent wheel lockup, making anti-skid essential for automated braking operations.

In-Flight Brake Use and Tyre Speed Limits

Wheel brakes may be used in flight for specific procedures, such as stopping wheel rotation after retraction. Tyre ground speed is limited by design to prevent excessive heat and structural damage, especially during high-speed operations.