From Conventional Navigation to PBN
Conventional Navigation is based in radio aids and is conducted mainly by indications to distances and bearings from VOR, DME and NDB equipment located on the ground and read by the on-board equipment.
The most basic form of instrument navigation involves flying a direct track between a succession of VOR or NDB beacons which are located on or close to the desired track.
The magnetic track and distance between successive beacons are measured and the calculated heading is flown, with corrections to allow for the effect of wind, until the next beacon is reached.
Whether beacon to beacon navigation is not possible or a curved trajectory must be defined, conventional navigation offers the possibility to fly radials between nav aids or constant distances.
Conventional navigation has several limitations:
Wider protection areas are required
Limited design flexibility
Area Navigation (RNAV)
RNAV is a method of navigation which permits the operation of an aircraft on any desired flight path; it allows its position to be continuously determined wherever it is rather than only along tracks between individual ground navigation aids. RNAV includes Performance Based Navigation (PBN) as well as other RNAV operations that are not within the definition of PBN.
Area navigation has several advantages:
Aircraft fly over waypoints instead of nav aids
Permits operation in any desired path within the nav aid coverage
Flight Management System estimates the position using navigation sensors and compares it to defined route
Required Navigation Performance (RNP)
Required Navigation Performance (RNP) is a family of navigation specifications under Performance Based Navigation (PBN) which permit the operation of aircraft along a precise flight path with a high level of accuracy and the ability to determine aircraft position with both accuracy and integrity.
RNP offers safety benefits by means of its precision and accuracy and it reduces the cost of operational inefficiencies such as multiple step-down non-precision and circling approaches.
The introduction of the FMS navigation system enables the estimation of the aircraft navigation error. The Total System Error (TSE) on aircraft navigation error considers the following components:
The path definition error is the difference between the desired flight path and the coded flight path in the Navigation Data Base (NDB).
The flight technical error is based on the piloting and flight guidance performance represented by the cross-track deviation (XTK).
The navigation system error is based on the aircraft position error computed by the systems
The Performance-Based Navigation (PBN) concept was created on the capability to quantify this Total System Error. On this basis, the PBN concept enables to design procedures that reduce the separation with obstacles and the separation between aircraft.
To achieve this objective, the PBN concept specifies the following basic definitions of navigation performance:
It defines the estimation of error on the computed aircraft position: The real aircraft position remains within a determined area for 95% of the flight time. The navigation accuracy is the radius of this determined area.
PBN defines a minimum navigation performance for the need of the different type of operations (RNP value). The navigation accuracy must be less than 1 x RNP value.
It ensures a high level of trust in the aircraft navigation computation: The real aircraft position remains within a determined area for 99.999 % of the flight time considering undetected navigation systems malfunctions. The navigation integrity is the radius of this determined area.
PBN defines a minimum navigation performance for the need of the different type of operations (RNP value). The navigation integrity is compared to 2 x RNP value.
It ensures the computation of navigation information all along the flight. This definition includes the Global Navigation Satellite System (GNSS) services.
Difference in tracks from Conventional Navigation to PBN