ATC Watcher:
What is more interesting is he obligation to follow certain rules to actually perform an RNAV-AR APP :you need certified aircraft, certified and trained crews , a certified airport and trained air traffic controllers . It is not because it is in the aircraft data base that you can use it . And there lies our first problem.
In the U.S. it won't be in your database unless all certification and qualifications have been met.
I would add to the experts take on RNP AR. AB's airplanes that can do RNP AR 0.30 approaches are ready and able to do RNP 0.10. If a pilot flying into VNTK is worried about being offset up to 0.30, he/she can force the FMS to use 0.10. Thus, the 5% probability maximum offset would be 608 feet. An FMS calculated exceedence in excess of RNP 0.10 would alert 'Unable RNP."
And, of course, the RNP AR pilot is always seeing a value for ANP.