Many times the terms RNP and RNAV are used interchangeably but Performance Based Navigation concept is one which marks clear distinction between both. Area Navigation (RNAV) is a method of navigation which allows aircraft to fly on any desired path within coverage of ground based, aircraft self-contained or air based navigation aids coverage. For the purpose of area navigation specified RNAV accuracy must meet 95% of the flight time.
With the further improvement of navigation systems method of navigation is shifting from sensor based to performance based. Performance Based Navigation system demands monitoring system performance and alert triggering in addition of RNAV accuracy.
RNP(Required Navigation Performance) is the index of performance requirement to operate in a given airspace in terms of accuracy, monitoring and alerting.
RNAV Airspaces and desired accuracy
- Basic Area Navigataion (B-RNAV)
+/- 5 nm for 95% of flight time
- Minimum Navigation Performance Specification (MNPS)
lateral deviation standard of 6.3 nm used in north Atlantic and few other regions
- Precision Area Navigation (P-RNAV)
+/- 1 nm for 95% of flight time
- Required Navigation Performance (RNAV-10 or RNP-10)
+/- 10 nm for 95% of flight time and requires no alerting. ICAO adopted RNAV-10 and RNP-10 same because of many areas adopted RNP-10 before the specifications were made and it was costly to change all manuals and charts.
- RNAV 1 and RNAV 2
+/-1 nm and +/-2 nm respectively for 95% of flight time
RNP Airspaces and requirements
- Required Navigation Performance-4 (RNP 4): +/- 4 nm for 95% of flight time with integrity, continuity, performance and alerting requirements. Used for oceanic and remote operations.
- Required Navigation Performance-2 (RNP 2): +/- 2 nm for 95% of flight time with integrity, continuity, performance and alerting requirements. Used for oceanic operations.
- Required Navigation Performance – 10 (RNP 10): same as RNAV-10
[ICAO Doc 9613, pg. I-(iii)] RNAV systems evolved in a manner similar to conventional ground-based routes and procedures. A specific RNAV system was identified and its performance was evaluated through a combination of analysis and flight testing. For domestic operations, the initial systems used very high frequency omnidirectional radio range (VOR) and distance measuring equipment (DME) for estimating their position; for oceanic operations, inertial navigation systems (INS) were employed. These “new” systems were developed, evaluated and certified. Airspace and obstacle clearance criteria were developed based on the performance of available equipment; and specifications for requirements were based on available capabilities. In some cases, it was necessary to identify the individual models of equipment that could be operated within the airspace concerned. Such prescriptive requirements resulted in delays to the introduction of new RNAV system capabilities and higher costs for maintaining appropriate certification.
[ICAO Doc 9613, pg. I-(iii)] Performance-based navigation (PBN). The PBN concept specifies that aircraft RNAV system performance requirements be defined in terms of the accuracy, integrity, availability, continuity and functionality, which are needed for the proposed operations in the context of a particular airspace concept. The PBN concept represents a shift from sensor-based to performance-based navigation. Performance requirements are identified in navigation specifications, which also identify the choice of navigation sensors and equipment that may be used to meet the performance requirements. These navigation specifications are defined at a sufficient level of detail to facilitate global harmonization by providing specific implementation guidance for States and operators.
Under PBN, generic navigation requirements are defined based on operational requirements. Operators then evaluate options in respect of available technology and navigation services, which could allow the requirements to be met. An operator thereby has the opportunity to select a more cost-effective option, rather than a solution being imposed as part of the operational requirements. Technology can evolve over time without requiring the operation itself to be reviewed, as long as the expected performance is provided by the RNAV system. As part of the future work of ICAO, it is anticipated that other means for meeting the requirements of the navigation specifications will be evaluated and may be included in the applicable navigation specifications, as appropriate.