[QUOTE]And yes, if the ANP remains below the RNP we can continue, even for a dual GPS loss on a GNSS approach.[QUOTE]
IIRC 738 with dual GPS receiver failure, you'll get a TERRAIN POS (or some verbiage to that effect) alert on the ND long before the ANP exceeds RNP. You're left with the magenta line (INS & DME/DME referenced) but the Terrain Display is removed (both from the ND & VSD) and I believe some EGPWS functions are degraded. With ANP gradually increasing but still less than RNP, do you continue under these circumstances?
Also IIRC 738 IAN can be used on an RNP (AR) approach as long as there are no RF turns involved. Many US RNP (AR) approaches have numerous transitions to a FAF on straight-in final approach, some of the transitions with RF turns (LNAV/VNAV req'd), but some with straight-in transitions (no RFs, IAN acceptable
AFAIK).