What is performance based navigation (PBN)?

Performance Based Navigation, or PBN, is navigation that uses global navigation satellite systems (GNSS) and computerised on-board systems. This is in contrast with traditional sensor-specific navigation based largely on fixed ground-based beacons guiding aircraft along published routes via waypoints defined by these beacons.

PBN defines aircraft navigation requirements in terms of the accuracy, integrity, continuity and functionality required for the proposed operations.

Navigation using legacy ground aids is ‘relative navigation’ since aircraft are always operating relative to the navaids — whether tracking to or from aids, or flying to a point defined by a VOR radial and DME distance from a ground station. PBN, on the other hand, is ‘absolute navigation’ — the aircraft operates by first determining its present position in terms of latitude and longitude, and then where this position is in relation to the intended flight path.

This has the major advantage of flexibility: providing the aircraft has a means of determining its current position, it can operate anywhere that positioning system will operate.

PBN encompasses two types of navigation specifications:

  • RNAV (aRea NAVigation), and
  • RNP (Required Navigation Performance).

The difference between the RNAV and RNP navigation specifications is that on-board performance monitoring and alerting is required for RNP but not for RNAV operations.

In an aircraft utilising a stand-alone GNSS, RNP is achieved through the use of Receiver Autonomous Integrity Monitoring (RAIM). Area navigation systems often integrate several sources of navigation information e.g. inertial and GNSS, to provide highly accurate navigation solutions.

These systems may use alternate means of aircraft autonomous integrity monitoring systems that are the equivalent of RAIM.

The on-board performance monitoring and alerting function ensures the integrity of the navigation solution i.e. the system is meeting the required accuracy.

Information from the GNSS calculates its position from the satellites in view. A timely warning is provided when the accuracy of that position falls outside an acceptable limit, alerting the pilot of the need to discontinue the approach.

For example, setting an RNP value of 0.3 NM means the on-board performance monitoring will alert the pilot if it estimates the error of the navigation system exceeds 0.3 NM.

The following diagrams show how ICAO navigation specifications have been adopted by CASA to contribute to global harmonisation of aviation safety regulations.

rnp_diagram

 

pbn2-navigation

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