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Can somebody explain why do A320 aircraft have an anti skid system? What is its purpose? And a brief explanation on how it works.

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  • $\begingroup$ Yes, specifically the 320 $\endgroup$
    – Johnson
    Dec 20, 2019 at 15:21

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It's very similar to Anti-Lock-Brakes on cars.

  1. The main reason aircraft have it is that a locked tyre will heat up, wear excessively and can burst (aircraft tyres are typically run at much higher pressure than cars or even HGVs).

  2. If you lock a wheel under braking, it no longer provides any steering. Aircraft might not be swerving around obstacles, but staying on the runway is more important than minimising stopping distance.

  3. A locked wheel generates slightly less than maximum stopping force. An automated system can hold the brakes at the point where it's not quite skidding, and brake harder than a human trying not to skid.

They work by monitoring the speed of each wheel, and releasing the brake on any wheel that slows down significantly more than the rest.

I believe that airliners are tested to check that locked wheel won't wear to the point where it bursts, but you can only do that once!

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  • $\begingroup$ If AS is inop when landing and you try to brake hard you will almost certainly lock the wheels and blow tires. $\endgroup$
    – John K
    Dec 20, 2019 at 17:19
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Robin, not only the A320 but all modern jetliners have anti-skid. Like the name suggests the system is to avoid the tires to skid. It works basically like an ABS but it's actually the ABS 2.0. The system brakes until just before the tires lock but without modulation like the ABS and it applies more pressure the less is the ground speed. Together with speedbrakes and reverse thrust it applies sufficient brake pressure to keep a steady de-acceleration. Ex: Autobrake 2 with speedbrake up and NO reverse thrust will have the same stop distance than Autobrake 2 with speedbrake up and Maximum reverse thrust. In this case, the brake pressure applied by the anti-skid will be less with the reverse thrust applied to keep the same stop distance.

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  • $\begingroup$ Autobrake and anti-skid are separate functions. Anti-skid is active even if braking manually, and just reduces the brake pressure when the wheels start to lock. It is a bit smarter in detecting that than the car systems, but there is no way to find the immediate coefficient of friction, so it still has to be reactionary. The autobrakes is a separete function that manipulates the brakes to achieve target deceleration. $\endgroup$
    – Jan Hudec
    Dec 20, 2019 at 22:31
  • $\begingroup$ Hi Jan, yes they are separate functions. I did not say otherwise. Thanks for clarifying. $\endgroup$
    – FONSPA
    Dec 21, 2019 at 2:28

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