You would if you were flying into a runway without a published RNAV-AR or RNAV-GNSS approach... such as the MEL 16 Twin NDB I mentioned (which has now been remedied). There may still be some airports available for diversions or emergency that do not have published RNAV approaches - I haven't checked lately.
QF have a CASA instrument allowing RNAV overlay approaches of NDB or VOR approaches without the navaids being serviceable or even installed on the aircraft. Doing this requires a CASA approval, which QF has (for it's GPS enabled aircraft).
Interestingly enough, as I indicated earlier, QF requires GPWS for RNAV-AR and RNAV-GNSS, but they do not require GPWS for NDB overlay approaches. GPWS doesn't fail every day but that's just an obscure example.
Last edited by HF3000; 3rd Dec 2012 at 13:39.