Autobrake and parking brake interference / RTO mode unreliable

[Stephan737]

Happy new year dear developers!

When using the RTO mode of the autobrake system in version 1.5.2 and performing a rejected take-off my parking brake gets applied to simulate the RTO function. However, after the rejected take off the parking brake kicks in every time I cut back the throttles to idle which makes it hard to reach the gate for my tire inspection.

Furthermore the RTO mode does not activate when A/C is on GND, average wheel speed is more than 88 knots and the throttles get retarded to FWD idle. These are the conditions my real world training manual as mechanic tells me. I have to use max reverse within a 1sec time period (from take-off power) in addition to the conditions just mentioned to activate the RTO mode. And even then the RTO function might fail from time to time (see my 2nd attempt in the video below). Am I missing something?

I've tried to record it. At take-off rejection above 90 knots I retarded both throttles to FWD idle. Nothing happened on the autobrake system. After 2 secs I deployed the thrust reversers and still the RTO function is not armed. After full stop you can see some trouble shooting with the system. On the 2nd attempt RTO stilll doen't activate at 120 knots GND speed and instantly going to max reverse. I applied manual brakes a couple of seconds later to save some of the light poles.

Should you discover the mistake between my ears and not in your system modelling feel free to let me know. ;-)

Couldn't find anything in the known bugs section or another thread related to this topic. Log file is attached below.

https://www.youtube.com/watch?v=37ODVzFEAW8

Best regards,

Stephan

Log.txt

[Litjan]

Hi Stephan,

I have also seen weird behavior on subsequent use of the brake system after activation of the RTO mode.

We are using the default X-Plane brake system, I am hoping for better modeling of various details on different aircraft in future versions of X-Plane.

[Litjan]

@Stephan737 I did some testing with our aircraft and the default 737-8 and I see some differences that I will investigate.

It seems that the trigger for the autobrake is GS > 100 and the thrust levers must have been > 0.5 throttle angle.

But the default 737 triggers the autobrake reliably when retarding the thrust levers (no reverse thrust needed) while our 737 only triggers it when moving the thrust lever back and then forward-back AGAIN. However the default 737 will also trigger the autobrake at very low speeds...

Also the default 737 will not engage the brake again after switching the autobrake selector to OFF, while our 737 will still apply it if the thrust levers were moved > 0.5 on subsequent taxiing.

So maybe there is something that LR did to tweak this that we are not benefiting from.

Edited January 9 by Litjan

[Litjan]

@Stephan737 It turns out that we DO override the default conditions for the arming of the RTO mode. You found a bug in the way we do that, thank you!

The default RTO mode is armed when the thrust levers are > 0.5... so the default 737 will also trigger it when you reject the takeoff at 30 kts.

We override this to require a speed of > 90kts (I changed this to 88 now), but we ALSO required the thrust levers to be at < 0.2! This is the mistake, because when Nils or Tom coded this, they thought that "yeah, the lever needs to be near idle for RTO to trigger...". But we do not TRIGGER the RTO mode, we just ARM it. And to TRIGGER it, X-Plane want the levers to be at >0.5.

So effectively you have to "double pump" the thrust levers to get the RTO function on our model. Once back to "arm" the RTO, then forward and back to "trigger it".

I never noticed because on my tests because I also immediately used max reverse like I was trained - which overrides this system and triggers the RTO mode anyway.

This will be fixed in the next updat.

The secondary problem of "RTO triggering again when trying to taxi" can be avoided by not pushing the thrust levers past 0.5. If you heed the maximum N1 of 40% during taxiing, this should not happen. However I need to find out together with Tom how we can avoid the RTO mode to trigger again with the selector in OFF - it should not engage, regardless of the thrust lever angle used.

Cheers, Jan