For each control surface, the letter in the box shows which hydraulic service is used and the number underneath on the architecture diagram shows which computer controls it.
So for example, the left (port) elevator is normally controlled by ELAC 2, using Green hydraulics. If ELAC 2 fails, OR Green hydraulics fail; control will be passed to ELAC 1 which will control the surface using Blue hydraulics.
If Both ELACs fail, control passes to SEC 2, using Green hydraulics. If both ELACS AND SEC 2, OR Green hydraulics fail; control passes to SEC 1 using Blue hydraulics.
The arrows show the sequence of the reconfiguration.
So there is a lot of redundancy !
Hope this helps.
Last edited by Uplinker; 24th December 2020 at 13:16.