The FMGS assumes you will turn onto final approach abeam the Final Aproach Course Fix for the approach loaded for track miles and fuel calculations.
This will be the CF, CI, CL, CB, CD, CV, CS, CN, CQ, CM or CR in the specified aproach.
For instance, an ILS my have a position CI27R.
This is why the miles indication at the bottom of the Flight Plan page is the best indication of track miles in the descent.
Incidently this doesn't work with the A340-200 (and I am guessing a few other older FBW airbusses) if a track offset has been inserted (software problem.
Hope this makes sense and helps.
Regards
Last edited by TAVLA; 26th Jun 2005 at 13:45.