There seems to be some confusion here. Yes the airbus can be flown in either heading and vertical speed mode or track and flightpath angle mode by pressing a button.
Normal navigation mode is heading and vertical speed.
For pilot interpreted non precision approaches where tracking is required from a beacon of some sort then track and flightpath angle is used (bird on mode)which simplifies the approach by automatically applying the drift correction and automatically correcting the descent angle selected for adjustments in airspeed so that if a 3 degree descent path is selected then you can vary your flap and speed selections at will and still maintain your descent angle.
This does present a problem if doing an SRA. The radar controller would like the airbus pilot to fly headings, no problem, but at the descent point the pilot would like to have the 'track and flightpath angle mode' purely for the descent angle feature because that takes out the requirement to keep on top of checking the ROD/VSI and adjust for varying speeds/configuration, but you cannot have heading mode selected along with flightpath angle.
Now, it is quite possible to fly the SRA in the basic mode of heading and vertical speed, it just needs some pilot input and a check of the required ROD versus groundspeed but it seems to contravene the airbus methodology and possibly outside the acceptable norm for some.
The SOP versus ATC requirement seems to be cropping up a lot lately!
