How Aircraft Antiskid Brakes Work?

Every pilot knows the panic of a skidding stop. Lock up a wheel during landing and you lose steering, you lose traction, and you lose braking power all at once. The antiskid system is one of aviation's most elegant safety solutions: a closed loop that measures what the wheels are actually doing and adjusts brake pressure dozens of times per second to keep them on the edge of skidding without going over. The core physics of wheel skid When a wheel locks completely, it stops spinning. But the aircraft is still moving forward at high speed. The tire then slides across the pavement with no grip at all. This is catastrophic during landing because sliding wheels generate far less friction than rolling wheels, and you also lose all directional control. The pilot cannot steer; the plane goes where it wants. The antiskid system solves this by monitoring wheel speed and preventing lock up before it starts. How the system senses the problem The antiskid computer watches the speed of each main landing gear wheel using a sensor on the wheel axle. As the aircraft slows during landing, wheel speed normally decreases smoothly. But if a wheel suddenly starts decelerating much faster than the others, the computer knows something is wrong. The pilot might have applied too much brake pressure, or the runway is wet or icy, or there is a flat spot forming on the tire. The system detects this rapid deceleration in just tens of milliseconds. The automatic brake adjustment The moment the computer senses a wheel trying to lock, it sends a signal to the brake actuator for that wheel. The actuator reduces brake pressure instantly. As soon as the wheel starts spinning again and regains traction, the computer increases brake pressure again. This cycle happens many times per second. The pilot feels the brakes pulsing or chattering under their feet, especially on low grip surfaces. This is normal and correct; it means the system is working. Why this matters for landing distance A skidding wheel is useless for stopping. A rolling wheel, even one on the verge of locking, maintains traction and generates powerful friction. By keeping all wheels rolling and on the threshold of skid, the antiskid system actually shortens landing distance compared to a pilot trying to brake manually on a slippery runway. The computer reacts faster than any human can, and it treats all wheels fairly, so stopping force is balanced across the aircraft. Redundancy built in Most transport aircraft have redundant antiskid systems. If one channel fails, a backup takes over. Some aircraft use independent channels for nose gear and main gear, so that even if one system fails completely, the other wheels still have protection. On the ground, technicians can test the system by spinning up the wheels on jacks and applying brakes while the computer monitors response.