More confusion - there are several standards of RNAV!
Apart from the Basic RNAV there are precision RNP10/RNP5 standards and the not yet introduced RNP1/3 that will be combined with ADSB. I suppose it is the basic RNAV that eagle737 noticed marked on the charts, but I know that some airports - Frankfurt for example - have some PRNAV approach options for aircraft equipped for precision RNAV.
Notwithstanding the physical aircraft fit, within EuroControl, each individual aircraft is required to carry a certificate issued by the airworthiness authority in the country of registration, stating the compliance standards of the navigation equipment carried, including with ACAS/TCAS II Ch 7, RVSM and RNAV. Obtaining the certificate is generally a paperwork exercise but it includes proving that the company Operations Manual includes procedures for using the equipment to operate in the designated airspace.
Unless the navigation fit is certified for RNAV you should not fly designated RNAV flight paths, regardless of one's opinion of the equipment carried. It is easy to discover the certified installation of the aircraft you are flying as the navigation performance certificate is carried on the flight deck, along with the certificate of airworthiness, radio station licence, certificate of insurance etc.