Thanx alot guys for the answers and the help! So I guess that most of the time the system informs the pilot about the switching from green to yellow by an ecam warning and the wheel page ALTN BRK message. But not in the case that I am trying to understand. I'll share it with you: autobrake not selected ( manual braking ), after touch down and an ecam BRAKES : AUTO BRK FAULT, PF starts braking and there is no braking. PNF notices in the triple indicator the yellow pressure rising on both sides while the PF is pressing the pedals. But there is still no braking. So we have here two weird things : 1) The system shifted from green to yellow without notification to the crew. 2) Pressure from yellow system did not reach the brakes, it surely reached the alternate servovalve ( antiskid ) as indicated by the triple indicator.
This is what I'm trying to figure out.
Thanx for any help.