RNAV systems use navigation signals from various ground and space-based NAVAIDs. Then they are able to define any location on the map in terms of latitude and longitude and display it as a waypoint. The airborne RNAV computer determines the present airplane position and calculates bearing and distance to or from any waypoint.
While conventional routes are paths between ground NAVAIDs, RNAV routes use waypoints. In this way, RNAV overcomes a major limitation of conventional navigation techniques, which require ground NAVAIDs overflying.
Required Navigation Performance (RNP) is the latest advancement in terms of RNAV systems. It defines the navigation performance required to operate in a particular airspace or on a designated route. RNP-approved systems provide the same onboard capability to conduct traditional RNAV operations. However, RNP systems enable on-board navigation performance monitoring and alerting.
According to the ICAO PBN concept, the RNAV 1 and RNAV 2 navigation specifications were primarily developed for operations in radar environments. RNAV1 is a harmonization between the European Precision RNAV (P-RNAV) and the U.S. Type B RNAV definition, while RNAV 2 corresponds to the previous U.S. Type A RNAV definition.
The RNAV 1 specification is similar to the European P-RNAV specification. However, although RNAV 1 requires the same navigation accuracy as P-RNAV (±1 NM, Table 02), P-RNAV does not satisfy all the requirements of RNAV 1.
For example, in Europe, P-RNAV permits the use of VOR/DME as the only input for position determination in limited circumstances. For more information on the differences between RNAV 1 and P-RNAV, refer to ICAO Doc 9613, Volume II, Part B, Chapter 3, section 3.3.2.4.
The RNP 1 specification was originally published as Basic-RNP 1 to distinguish from a specification named Advanced-RNP 1, which was initially planned. But Advanced-RNP 1 evolved into Advanced-RNP and the prefix “Basic“ was no longer necessary. For this reason, ICAO adopted the term RNP 1 instead of Basic-RNP 1. Existing approvals granted under the original nomenclature remain valid.
RNP 1 allows the development of routes to connect Enroute and terminal airspaces with no or limited ATS surveillance and with low to medium density traffic.
The RNP 1 specification relies on GNSS. Some RNAV systems based on DME/DME are also able to achieve the RNP 1 accuracy. However, RNP 1 is primarily intended for environments where the DME infrastructure is not able to support DME/DME area navigation with the required performance.