Part 1: PBN – Performance Based Navigation

PBN concept represents the shift from sensor based navigation to performance based navigation. PBN primarily identifies navigation requirements irrespective of the means by which these are met. These navigation performance requirements are identified as navigation specifications which also identify the choice of navigation sensors and equipment that may be used to meet the performance requirements.

PBN needs two fundamental aspects:

  • Navigation Specification
  • NAVAID infrastructure – can be ground and/or space-based
Navigation Specification

It is the set of aircraft and pilots’ requirements needed to support a navigation application within a defined airspace concept. Navigation Specification defines the performance required by RNAV or RNP system as well as any functional requirement such as ability to conduct curved path procedures or to fly parallel offset routes.

PBN Navigation Specifications

RNAV or RNP systems : They are fundamentally similar area navigation system with key difference of requirement for on-board performance monitoring and alerting in RNP system. Navigation specification requiring on board navigation performance monitoring and alerting is referred to as RNP specification and one which don’t have such requirements are referred as RNAV specification.

Note:

  • Specific performance requirements are defined for each navigation specification and for this reason aircraft approved for particular navigation specification is not automatically approved for any other navigation specification.
  • No comparison in form of GOOD or BAD can be made between these navigation specifications. Simple is to understand that they are just different.
NAVAID Infrastructure
As stated above, PBN primarily identifies navigation requirements irrespective of the means by which these are met. Accordingly NAVAID infrastructure can be ground based (VOR, DME, etc), aircraft based (IRS, INS etc) or space based (GNSS) or any combination thereoff.

Key Points on PBN:

  1. ICAO DOC 9613 is manual on PBN
  2. It is expected taht all future RNAV applications will identify the navigation requirements through the use of performance specifications rather than defining the equipage of specific navigation sensors
  3. Transition to PBN may not be necessary where procedures are already established but future area navigation procedures should use the process and description established in ICAO DOC 9613
  4. Concept of RNP is fundamentally same as RNAV but more stringent as it demands on board performance monitoring and alerting facility.
  5. Not all but most of the modern systems developed after 1990 provide on board performance monitoring and alerting so there can be airspace which allows only RNP operations and also airspace where both RNP and RNAV coexist.

Advantages of PBN:

  • reduce the need to maintain ground based sensor and associated cost
  • call for more efficient use of airspace
  • provide more flexibility with better accuracy
  • clarifies the way in which RNAV and RNP systems are used

Scope of Performance Based Navigation

Lateral Performance Vertical Performance
PBN is limited to operations with linear lateral performance requirements and time constraints due to legacy reason associated with previous RNP concept. In approach phases of the flight PBN accommodates both linear and angular laterally guided operations. Some approaches include requirements for vertical guidance (using augmented GNSS or Barometric VNAV). However, these requirements do not constitute vertical RNP which is neither defined nor included in the PBN Concept.

On-board performance monitoring and alerting

This is the main element that determines if navigation system complies with the necessary safety level associated to an RNP application. It relates to both lateral and longitudinal navigation performance and also allows the crew to detect any issue with navigation system. Because of said issue, navigation system may not be achieving or may not guarantee with 10-5 integrity, the navigation performance required for the operation.

Functional requirements of RNAV and RNP specifications

  • continuous indication of aircraft position w.r.t to track on navigation display
  • display of distance and bearing to active way-point
  • display ground speed or time to active way-point
  • navigation data storage function
  • failure indications for RNAV or RNP system
  • there may also be requirement for navigation database and capability to execute database procedures

RNAV and RNP designations

  • navigation accuracy is the only one of the functional and performance requirements included in navigation specification
  • functional and performance requirements are defined for each navigation specification and an aircraft approved for one specification is not automatically approved for other specification (e.g. RNP 0.3 specification is not automatically approved for navigation specification having a less stringent accuracy requirement e.g. RNP 4)
  • these navigation specifications are simply different, there is no good or bad comparison
  • navigation application (e.g. SID/STAR) is designed using the navigation specification (e.g. RNAV 1) based upon a specific NAVAID infrastructure (e.g. GNSS); which may be different in another state (e.g. RNAV 1 SID in one state my call for GNSS mandatory while in other state there may not be GNSS requirement)

 

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