PENKO
There is no function to extend the centre line in Airbus FMGS except if you select the RW only. This is a radial in function. It extends the radial. On some NPAs the RW heading and inbound final approach track is different and you need to extend the inbound track. Extend centre line is a misleading term. Some tend to think that it is done to help turn inbound and not to get NAV during GA. No Airbus document uses this term.