RNAV and RNP Differences
RNAV airspace generally mandates a certain level of equipment and assumes you have a 95% chance of maintaining a stated level of navigation accuracy.
RNP is a part of Performance Based Navigation (PBN) which adds to the same RNAV accuracy standards a level of system monitoring and alerting.
RNAV 1 and RNP 1 both state a requirement of a 95% probability of staying within 1 nm of course. RNP will alert pilots when the probability of the aircraft staying within 2 nm of that position goes below 99.999%.
Under RNAV, the required equipment used to achieve the navigation accuracy is specified.
Under PBN, only the Required Navigation Performance is specified and it is up to the operator to achieve that performance .
The key difference with RNP: Onboard Monitoring and Crew Alerting
ONLY for Flight-Simulation!