If you want button, controlling airbrake, to be depressed, try this way.
Button numbers are for example only.
Physical button 11 controls trigger. Virtual button 15 controls airbrake. But. 11 configured as toggle. #11 sets trigger = #15. After Toggle time expired #11 releases (while you still press button) but #15 stays depressed. Second toggle button is #13 resets trigger. When you release button physically, virtual #13 pulses, resetting trigger. #15 releases, closing airbrake.
Another way. Configure your button as Button Alternate. Press and release. Its virtual child stays depressed until you press button again. No triggers, direct airbrake control.
Be lucky!