I was reading in the Airbus A320 FCTM regarding the dual engine failure procedure. The ECAM tells us to recycle FAC 1 OFF THEN ON. Why do we have to recycle FAC 1 specifically? I opened the QRH and it shows this also.
- Resetting FAC 1 enables the recovery of characteristics speed displayed on the PFD.
- Resetting FAC 1 also enables rudder trim recovery, even if no indication is available.
- When the hydraulic power is lost, the right aileron is lost, and is in the upfloat position.
- Rudder trim may be used to compensate for this upfloating aileron.
This is from the QRH under 'ENG DUAL FAILURE'. That answers why FAC 1 is reset.
FAC 2 on the other hand (unlike FAC 1) is not powered by the emergency electric system, see § Flight Control System - Electrical Supply. And that's why you don't cycle FAC 2.
From the same section FAC 1 is not on a hot (stand by) supply, so after a power interruption it requires a reboot (my interpretation).
Do not use for flight.