Here is the procedure for performing an RNAV approach in the A300:
You cannot be in a profile mode. Must be in LVL CHG or V/S
You descend to the platform altitude of the approach
Go to TO/APPR page and type in the MDA
Then a prompt will appear saying 'Final X.X'
Execute that prompt and the glide will appear
Most usually 3.00 degrees.
Once activated, you will see a top of descent arrow at the final approach fix.
You need to be level at your platform altitude before your final approach fix.
Once in ALT HOLD (at this altitude) press PROFILE
You will see on the FMA P.DES appear armed in blue
30 seconds before the descent it start to flash to signal descent will appear. It will descend on the glide as soon as it receives glide path signal. NO NEED TO LAND OR V/L.
Hope this is helpful.