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Autobrake dissarm


Joan Alonso

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I’m struggling with that, because I can not figure out why it happens. The autobrake (low and medium) works ok sometimes, but sometimes just dissarms itself at touchdown. I tried a lot of things but I can not find what triggers the ABRK dissarm. I just found some old topics that discuss the same behaviour with the old buses. There’s a modified xml file but it is not downloadable anymore.

 

So, what I tried so far with no luck:

 

- Different Thrust Cut Idle buttons

- Different manual brake button

- Buttons tried through FSUIPC and without it

- Checked no button conflicts

- Wait to apply Rev Thrust on nose wheel touchdown.

- Tried both Low and Med Abrk

- Manual and Autoland

- Soft and hard touchdown

- Moving Thrust from CLB to MCT and back to CLB during approach (And tried also without doing it).

 

In all situations it was totally random.

 

As I said, it works sometimes, I would say 6 times of 10. But I can not understand why it disconnects itself the other four times.

 

Any ideas?

 

Thanks

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check your axis for brakes.  If there is any kind of braking being applied (improperly calibrated axis or what ever) then auto brakes will disconnect and manual braking applies.

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1 hour ago, bill3810 said:

check your axis for brakes.  If there is any kind of braking being applied (improperly calibrated axis or what ever) then auto brakes will disconnect and manual braking applies.

 

I’m using a single button for brakes. No pedals here, nor differential braking.

 

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22 hours ago, Joan Alonso said:

 

 

I’m using a single button for brakes. No pedals here, nor differential braking.

 

I would also recommend looking at every single device you have hooked up and make sure the brakes aren't double assigned by accident.  I don't know of any other issues like this with the Autobrakes.

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19 minutes ago, bill3810 said:

I would also recommend looking at every single device you have hooked up and make sure the brakes aren't double assigned by accident.  I don't know of any other issues like this with the Autobrakes.

 

Thanks! But as I said I double checked and I made sure there were no button/hardware conflicts. It was the first thing I looked at when I realized this was happening.

 

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Ok. After more tests, not touching any key or button until touchdown: before dissarming the DECEL appears for just half a second, then the autobrakes dissarms completely. This is what confuses me, the only one condition I can think of triggering the dissarm is that the aircraft thinks that there’s been a bounce and disconnects itself? Obviously it does not happen bouncing, even occurs in very soft landings.

I really do not know what more to do, I tried some xml tweaks with no luck. Went back to the original again, waiting for some bright idea.

 

 

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Ok. I waited several flights to be sure but seems that the problem is gone.

I had to modify the ABRK.xml in order to force the ABRK system not to disengage before two premises: the aircraft must be on ground (seems that on some landings the system felt a non-existent bounce and disconnected itself) and half pressure of toe brakes is applied.

The last one works only with LOW brake mode.

With MED the system still applies the first premise, so I deduce that is the one that makes the system reliable now. Toe brakes pressure is just a reinforcement just in case you press the button/key unintentionally on rollout.

 

Anyway, solved finally.

Thanks.

 

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