Airbus DDRMI heading supply
 

In case of IR 1+3 TOTAL FAIL shouldn't the DDRMI heading reference be lost?

Why isn't DDRMI listed in the INOP SYS list of such a failure?

I can only think because the DDRMI VOR/ADF needles still work...might it be?

1-34-30 p6

Yes, I guess DDRMI is inop in that case.

If it was an ADF only DDRMI you could still have relative bearing from the needles, I guess. But with VOR needles, indications would be totally wrong.

The DDRMI has conventional red fail flags, so there is no need for being in the INOP list. Other stuff that is lost when you have electrical failures is not in the list, either.