Most FMCs already give the RNP against ANP (Required Nav Performance versus Actual Nav Performance). There is always a RNP. On the North Atlantic it is 12 (I think). Over most of Europe it is 5. But his is to change to 2 on 1 Nov 04. One of the difference is that you have to have a graphic display of Nav track dispalcement which does not mean an HSI swithced to INS instead of Nav. My company is going to have to fit glass Nav displys in it's classic jets as will all operators who want to use RNP2 airspace.
PS: I'm willing to be corrected on any of the figure above.