Autobr4ke. Again .-.

[SkyFly]

Hello!

Numerous people have brought up complaints about the autobrake not working sometimes for appearently no reason, myself included.
After tideous testing I found out:.

When the reversers are activated before the nosewheel is on the ground, the autobrake fails to work.
If you wait with reverser deployment until the nose gear is down on the ground, the autobrake works fine.
Oddly enough, I can hear the parking brake clicker when the autobrake activates. That´s how I immediatly hear if it works or not, even without looking at datarefs.

It´s all weird. I don´t see this behaviour on any other airccraft.

Tested about 100 times.
 

[Litjan]

Ha, good find - yet I am confused that this happens only on our aircraft - we are using the default X-Plane system for both reverse thrust and the autobrake, so I would assume similiar behaviour on the default 737, for example...

I will see if I can find out what is happening.

Thanks for the hint, Jan

 

[Iain]

I've not heard any complaints about autobrake not working for no reason, usually there is an explanation for it, such as toe brakes being applied by pedals, or spoiler not armed etc.  I can say in the last few months I have landed 100 times, every time the reversers are on before the nose gear touches, and the autobrake works just fine.

I done 3 short hope last night with the latest beta (KPVD-KBED-KASH-CYQL) and all working perfect.

Here is my landing at EGPE a week ago, autobrake 3 (prob should have used max) and you can see I switch to manual braking at 1:21 (autobrake disarm light isn't visable).

Again, no manual braking, reversers active as soon as mains touch, and never any problem.

You would not get any autobrake in this situation?

 

 

Edited July 24, 2020 by Iain

[Litjan]

I still have to try - but there is one thing to consider: If the thrust levers are advanced into forward thrust, they will disarm the autobrake. So even a little bit of thrust still set at touchdown will disarm them.

Now normally the reversers will not deploy while the thrust levers are not at idle - but I don´t know how X-Plane handles that. I could see a scenario where the pilot lands with the thrust levers not completely at idle, or maybe advancing them again before the plane registers that the reverse thrust is active (the dataref needs a second to switch).

The real plane will not allow the reverse levers to be pulled back before the reverse sleeves are in the fully deployed position, while X-Plane may allow that.

So a good test would be to touch down with idle thrust, keep the nose up, deploy reversers, keeping the nose up, then adding reverse thrust when the reversers are definitely deployed (it takes 2 seconds or so). You could actually start deploying the reversers when radar altitude is below 10 feet, but that is really bad piloting technique, so I don´t even want to encourage that ;-)

Cheers, Jan

 

Edited July 24, 2020 by Litjan

[SkyFly]

Yello Yall.

 

Jan,

On 7/24/2020 at 9:18 AM, Litjan said:

I still have to try - but there is one thing to consider: If the thrust levers are advanced into forward thrust, they will disarm the autobrake. So even a little bit of thrust still set at touchdown will disarm them.

Now normally the reversers will not deploy while the thrust levers are not at idle - but I don´t know how X-Plane handles that. I could see a scenario where the pilot lands with the thrust levers not completely at idle, or maybe advancing them again before the plane registers that the reverse thrust is active (the dataref needs a second to switch).

The real plane will not allow the reverse levers to be pulled back before the reverse sleeves are in the fully deployed position, while X-Plane may allow that.

So a good test would be to touch down with idle thrust, keep the nose up, deploy reversers, keeping the nose up, then adding reverse thrust when the reversers are definitely deployed (it takes 2 seconds or so). You could actually start deploying the reversers when radar altitude is below 10 feet, but that is really bad piloting technique, so I don´t even want to encourage that ;-)

Cheers, Jan

 

this was a good hint. I´ll do some further testing within the next days

[Litjan]

Yep, I will try to test this tomorrow as well!

Cheers, Jan