This table details the different Nav Specs that are applicable in the different flight phases.
The table above details the individual navigation specifications in terms of their use in different phases of flight. Note that there are limitations and the reader should refer to the PBN Manual (ICAO Doc 9613 Edition 5) to fully understand these limitations.
As shown above, the Navigation Specifications are primarily considered to support specific phases of flight; historically, the single execption was Advanced RNP (A-RNP) which had been foreseen as an 'umbrella' specification covering all phases of flight. Today with the release of ICAO Doc 9613 (Ed 5), this specification can not be used in the Final Approach Segment (FAS).
In most phases of flight RNAV or RNP specifications can be utilised; however, when we consider the approach phase of flight and navigating inside the Final Approach Fix or Point (FAF/FAP) using only the on-board navigational capabilities, then the aircraft must have On-board Performance Monitoring and Alerting (OBPMA). Therefore, all approach specifications are RNP.
A Factsheet on RNP Approaches can be found here.