RNP, RNAV and ANP
Required Navigation Performance (RNP) is a type of performance-based navigation (PBN) that allows an aircraft to fly a specific path between two 3-dimensionally defined points in space. RNAV and RNP systems are fundamentally similar. The key difference between them is the requirement for on-board performance monitoring and alerting. A navigation specification that includes a requirement for on-board navigation performance monitoring and alerting is referred to as an RNP specification. One not having such a requirement is referred to as an RNAV specification.
RNP also refers to the level of performance required for a specific procedure or a specific block of airspace. A related term is ANP which stands for “actual navigation performance”. ANP refers to the current performance of a navigation system while “RNP” refers to the accuracy required for a given block of airspace or a specific instrument procedure.