On the EFIS of Airbus you can see 1FD2 on the autopilot section of the FMA. what does it mean?
It means that both Flight Directors are engaged:
Flight Director (FD) Engagement
The FDs are engaged automatically whenever the FMGC powers up.
- The symbol "1FD2" appears on both PFDs.
- No FD bars appear on the PFDs. The PFD displays FD orders when a mode is active on the corresponding axis.
- The FCU windows display dashes.
(A320 FCOM Autoflight - Flight Guidance)
It will look something like this:
The pilots can disengage one or both FDs. In this case -FD2, 1FD- or nothing will be displayed.
Manual Flight Director Disengagement
One FD off:
- The FD bars no longer appear on the associated PFD.
- The corresponding FD is disengaged.
Both FDs off:
- The FD bars disappear on both PFDs.
- If no AP was engaged, lateral and vertical modes disengage. The A/THR, if active, automatically reverts to (or remains in) SPEED/MACH mode.
- If one AP was engaged when the FDs are switched OFF, this AP remains engaged in the active modes but the FDs are no longer displayed.
If one FD fails, the other one will be used to provide guidance on both PFDs. In this case 1FD1 or 2FD2 will be displayed.
Automatic Flight Director Disengagement
If one FD fails or one FMGC is not valid, both PFDs display the remaining FD.