BOAC
Interesting stuff. I take it then, without a working database or Nav updating you could not easily navigate a VOR based airway and you would have to fly the VOR approach or airway c/line in heading, tracking the bar, which I take it is displayed in 'ROSE VOR' - or is it an RDMI job?
Right on both counts.
Selecting VOR Switch givng you Rose VOR on the Nav Display (ND) and there is also the VOR standby VOR which gives you two needles = VOR 1 and 2 respectively, or VOR 1 and ADF 1 or VOR 2 and ADF 1 (or ADF 2 for over water ops - )
By inserting the freq into the RAD page and/or hard tuning on the RMP - keep the needles in the middle on the NAV ROSE, or in the case of the standby VOR keeping the needle on the . . . bearing on the compass card.
The bearing being the bearing to the VOR, or the NDB.
Its a magnetic bearing.
The whole thing is a DDRMI, like you said - and is a function of the ADIRS (INS effectively) all flags show if ADIRS is TU.
Although the hard tuning on the Radio Management Panel (RMP) removes the tuning from the FMGC with a 1 or 2 ADIR failure - a total failure of the ADIRS (would remove any meaningful heading info on your compass card as it is dead anyway) but would leave you without a VOR.
As far as I can gather, there is no stand alone VHF VOR back up - I may be wrong, but I think not. In retrospect, however, you may get away with tuning on VHF 3 but that would not give you any display and the tuning range of the digits may not facilitate the lower VOR freqs. . . .?
But in that case one would have bigger fish to fry and you would have to adjust heading every 10 mins if attempting to track a great circle track, calculate convergency, and so forth. Back to DR. Hello Linberg, Brown, Alcock and the like.