Explain How Autobrake Levels and Brake Temps Work

[TurdFerguson]

I've never understood the limits of brake temps, and what to do to figure out the Autobrake levels in airliners in general. Can someone explain like I am a 5th grader on how this is determined, and is this procedure similar on other airliners?

 

Also, what brake temps do I have to achieve on the 300 and 310 for my airline to be mad at me after I land?

Edited October 30, 2021 by TurdFerguson
Changing title.

[Cammac]

Hi,

Thanks for your post. 

Autobrake systems are quite complex but actually picking which setting you need is not too complex in the A300 / A310 family. The auto brake system aims for a deceleration rate. So LOW and MED do not always physically apply the same break pressure. 

So how in the real world will this effect stopping distance and break temps? Well if you land with autobrakes low and do not select any REV THR you will actually stop in exactly the same distance if you select MAX REV THR why? Well this comes down to that deceleration rate if it can match that rate without using much breaking pressure at all it will do so and leaves the breaks cooler in the process with less wear. MED works the same way but of course has a higher target declaration rate.

On landing you will see the blue armed light change into a solid green bar, this only happens when 80% of that target declaration is achieved so on snowy runways you actually may never be able to get that, this is normal and is part of the system working as normal. 

But back to your main question of which setting do you use and when. In the A310 and up and coming A300 V2 you have a landing distance calculator and this will tell you if LOW or MED will allow you to stop on the runway you want to land on. But as a general rule runways under 2200 meters think about using MED and over that LOW should be fine. MAX can be selected in the air but the FCTM and FCOM say it should not really be used for landing. 

 Brakes HOT will happen quite often after landing if you are using the autobrakes. This is fully realistic as carbon brakes absorb quite a bit of energy and 5 minutes after landing they will be at the hottest temperature. A technique used by real A300 / A310 pilots to keep the brakes cool is to land with no auto brakes let it slow down the first part of the landing roll using no braking at all. Then smoothly apply braking as needed in 1 single application. Carbon brakes get hot due to amount of applications not only the amount of force.

Hope this answers your question.

kind Regards,

Lead Technical Team

[Umi Akai]

BTW from our FCOM, it's only recommended to switch brake fan after landing and 1.Brake temperature goes over 500C or,2. when arrived at gate and stopped.

It's not recommended to switch fans on as soon as you get BRAKE HOT caution, because it'll cause uneven cooling (or hotting) of brakes.