Attitude/Direction Indicator Flag
 

Hi all,

I've been trying to figure out the operation of the 3 axis ADI fitted as a standby instrument to the later Harriers (a Ferranti FSI100 I think). I see that there are 2 warning flags on it. The "Power" one seems pretty self explanatory to me but I can't figure out the "DG" (Directional Gyro) flag. I appreciate that on this type of instrument, the pilot must manually align the direction indicator with the magnetic compass (at worst - I realise more sophisticated data is normally available) but I don't really understand what the DG flag would be telling the pilot. Surely if the gyro is still running then it would provide as good a heading as it would pitch & bank angle, so does this mean that somehow directional indication is being maintained from some other source?

Many thanks in advance.

EDIT: I'm wondering if I should have posted this to the military forum. I figured it was a pretty generic question but perhaps I'm wrong. Are any of the moderators able to move this to a better place? Ta.
EDIT: Anyone?