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Safety Argument for PRNAV in Terminal Airspace

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The main aim of this Safety Argument is to provide a coherent structure and sufficient evidence to support the claim that P-RNAV in Terminal Airspace will be acceptably safe.


This document addresses the specification stage of the P-RNAV concept only.

Top Level Claim

P-RNAV in Terminal Airspace will be acceptably safe.

General Assumptions

The document refers to a series of assumptions made during the Safety Assessment and also to those made by JAA TGL 10.

Safety Assessment Assumptions

  1. It is assumed that the current level of risk presented by conventional approaches and departures is tolerable.
  2. The current separation minima between aircraft, in the horizontal and vertical dimensions, will apply under P-RNAV operations and that route spacing will not change.
  3. The requirements for obstacle and terrain clearance under P-RNAV will be as specified currently in ICAO Doc 8168 (PANS-OPS).
  4. The airborne equipment fit is capable of P-RNAV performance in accordance with the defined standard for the area(s) in which operations are intended. This includes achieving lateral track keeping accuracy of better than +/-1NM for 95% of the flight time.
  5. The navigation infrastructure, both ground and space elements, meets with defined standards.
  6. Controllers will exercise similar levels of deviation detection performance as for that achieved using current techniques.
  7. P-RNAV procedures will be flown using GNSS or DME-DME.
  8. Where adequate GNSS or DME coverage is available it is assumed that the effect of any VOR source has a negligible adverse impact on position determination.
  9. Before any VOR/DMEs are removed from Terminal areas there will be a safety assessment of the impact on RNAV procedures (i.e. contingency arrangements in case of loss of RNAV capability, cross checking capabilities etc.)

The following assumptions are declared in TGL10, section 4.

  1. All terminal P-RNAV procedures:
    • are consistent with the relevant parts of ICAO Doc 8168 PANS OPS ;
    • are designed following the guidelines of EUROCONTROL document NAV.ET1.ST10 “Guidance Material for the Design of Procedures for DME/DME and GNSS Area Navigation’ , as amended, or equivalent material;
    • take account of the functional and performance capabilities of RNAV systems and their safety levels as detailed in TGL10;
    Particular attention should be given to the constraints implied by the certification objectives of TGL10 paragraph 6.
    • take account of the lack of a mandate for vertical navigation by ensuring that traditional means of vertical navigation can continue to be used;
    • support integrity checking by the flight crew by including, on the charts, fix data (e.g. range and bearing to navigational aids) from selected waypoints.
  2. All routes/procedures are based upon WGS 84 coordinates and its realisation in ETRS 89 or equivalent.
  3. The design of a procedure and the supporting navigation infrastructure (including consideration for the need of redundant aids) have been assessed and validated to the satisfaction of the responsible airspace authority demonstrating aircraft compatibility and adequate performance for the entire procedure. This assessment includes flight checking where appropriate.
  4. If the procedure allows a choice of navigation infrastructure, e.g. DME/DME, VOR/DME or GNSS, the obstacle clearance assessment has been based upon the infrastructure giving the poorest precision.
  5. The required navigation aids critical to the operation of a specific procedure, if any, i.e. those which must be available for the required performance, are identified in the AIP and on the relevant charts. Navigation aids that must be excluded from the operation of a specific procedure, if any, are identified in the AIP and on the relevant charts.
  6. Barometric altitude compensation for temperature effects is accounted for in accordance with current approved operating practices. (Temperature compensation is not addressed as a special P-RNAV consideration in this leaflet).
  7. The supporting navigation infrastructure, including the GNSS space segment, is monitored and maintained and timely warnings (NOTAM) are issued for non-availability of a P-RNAV procedure, if navigational aids, identified in the AIP as critical for a specific P-RNAV procedure, are not available.
  8. For procedures which allow aircraft to rely only on GNSS, (see paragraph 5.1), the acceptability of the risk of loss of PRNAV capability for multiple aircraft due to satellite failure or RAIM holes, has been considered by the responsible airspace authority. Similarly, the risk is considered where a single DME supports multiple P-RNAV procedures.
  9. The particular hazards of a terminal area and the feasibility of contingency procedures following loss of P-RNAV capability are assessed and, where considered necessary, a requirement for the carriage of dual P-RNAV systems is addressed in the operational approval for the aircraft and, if appropriate, identified in the AIP for specific terminal P-RNAV procedures, e.g. procedures effective below the applicable minimum obstacle clearance altitude where RNAV is required for the safe recovery of the aircraft or where radar cannot be used for the purposes of providing guidance to an aircraft with a failed RNAV system.
  10. Where reliance is placed on the use of radar to assist contingency procedures, its performance has been shown to be adequate for that purpose, and the requirement for a radar service is identified in the AIP.
  11. RT phraseology appropriate to P-RNAV operations has been promulgated.
  12. Navigation aids, including TACAN, not compliant with ICAO Annex 10, are excluded from the AIP.

Please refer to Paragraph 8.4 of the document for details.

Associated Hazards

Related Regulations and Standards

  • JAA Temporary Guidance Leaflet, TGL 10 - Airworthiness and Operational Approval for Precision RNAV Operations in Designated European Airspace, Rev. 1
  • ICAO Doc. 8168 “Aircraft Operations, PANS-OPS”, Vol. II, March 2007, Edition 5
  • ICAO Regional Supplementary Procedures, EUR Region (Doc 7030/4).
  • EUROCAE/ RTCA ED76/ DO200A “Standards for Processing Aeronautical Information”
  • EUROCONTROL (2007): “Integrity of Aeronautical Information - Aeronautical Data Origination”, May 2007, version 3.1, ANT 43
  • EUROCONTROL Standard 003-93 - Operational Requirements and Functional Requirements for Area Navigation Equipment
  • EUROCAE/ RTCA ED-75A/ DO-236A “Minimum Aviation System Performance Standards: Required Navigation Performance for Area Navigation”
  • EUROCONTROL (2001): “ESARR4 Risk Assessment and Mitigation in ATM”, Edition 1.0

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