43RD ANNUAL CONFERENCE, Hong Kong, China (SAR), 22-26 March 2004WP No. 99Review of Policy on Precision Area NavigationPresented by SC1 |
Introduction
1.1 Precision Area Navigation (P-RNAV) procedures are being introduced in various regions of the world. IFATCA has previously established policy for P-RNAV. However, the last P-RNAV policy was created and adopted in 1994.
1.2 P-RNAV procedures have developed considerably since 1994. SC-1 has therefore undertaken a comprehensive review of P-RNAV procedures and existing IFATCA policy on P-RNAV.
1.3 This paper identifies new and emerging P-RNAV procedures and recommends changes, where required, to IFATCA policy.
Discussion
2.1 En-Route
2.1.1 P-RNAV applications are intended primarily for introduction into terminal airspace. Existing Basic Area Navigation (B-RNAV) procedures have been in use in En- Route airspace for numerous years and B-RNAV has been mandated in several areas. For instance, the carriage of B-RNAV equipment was mandated in ECAC airspace in 1998.
2.1.2 B-RNAV, which has an associated lateral navigation accuracy of 5 NM, is generally adequate for use in the majority of En-Route environments. The introduction of B-RNAV has enabled several benefits to ATS Providers to be realised, including improved design flexibility resulting in increased airspace flexibility. The ability to place routes where they are best suited, rather than being constrained to ground-based navigational aids, means that ATS routes can be better positioned, resulting in potential capacity increases. In non-radar environments, the introduction of B-RNAV has enabled reductions to take place in the amount of Procedural Separation Minima required between routes. It is possible that the introduction of P-RNAV in high density En-Route airspace may further improve airspace utilisation by permitting routes to be spaced closer together, as the lateral navigation accuracy of P-RNAV is 1 NM. This improved lateral navigation accuracy enables routes to be placed closer together, thereby increasing capacity for a given volume of airspace.
2.2 Terminal Areas
2.2.1 RNAV operations in Terminal Areas, where issues such as traffic density, route interaction, complex traffic flows and terrain clearance start to come to the fore, generally require a more stringent navigational accuracy than that used for the en- route environment.
2.2.2 P-RNAV offers the ability to use RNAV functionality in all phases of flight, except final approach and missed approach. This allows the routes in terminal airspace to be defined to best meet the needs of the airport, the air traffic controller and the pilot. This often means shorter, more direct routes with simple connections to the en-route structure. However, where environmental issues play a major role, the route can be designed to make best advantage of the airspace available and, where possible, by-pass densely populated areas. Careful design can also result in appropriately segregated arrival and departure streams, thereby reducing the need for radar vectors and hence the workload for both the pilot and the controller. Fewer radar vectors also means less uncertainty on the flight deck with regard to the anticipated tactical route and the distance to go.
2.2.3 In the ECAC region, action is being taken by EUROCONTROL to promote the use of improved lateral navigation accuracy below the Minimum Safety Altitude (MSA). It is generally considered that the 5 NM lateral navigation accuracy offered by B- RNAV is not sufficient below MSA. The use of B-RNAV below MSA is, therefore, effectively being prohibited and the use of a new standard, Precision Area Navigation, or P-RNAV, is being encouraged.
2.2.4 P-RNAV defines the standard for Terminal Airspace RNAV operations in the ECAC area. Aircraft operating according to the P-RNAV standard are required to satisfy a track-keeping accuracy of ±1 NM for at least 95% of the flight time.
2.2.5 P-RNAV is the aircraft and operator approval requirement that is advocated for RNAV procedures in ECAC Terminal Airspace. Terminal Airspace operations for which P-RNAV should be used include departures, arrivals, and approaches up to the point of the Final Approach Waypoint (FAWP).
2.2.6 The P-RNAV concept is spreading beyond Europe. The United States is adopting the P-RNAV standard. AC 90-96A is being developed and will both expand the current guidance and include new guidance for P-RNAV approval, and provide a logical transition from current B-RNAV approval to P-RNAV approval. AC 90-96A references JAA TGL-10 for technical requirements for P-RNAV. AC 90-96A is currently under review by the Terminal Area Operations Aviation Rulemaking Committee (TAOARC).
2.2.7 Terminal Airspace procedures that require P-RNAV approval are designed following common principles that ensure that procedure design and execution are fully compatible. Additional to the minimum performance and functional requirements appropriate for Terminal Airspace RNAV operations, P-RNAV approval also covers navigation data integrity requirements and flight crew procedures.
2.2.8 The most important aspect that P-RNAV offers is the consistency in RNAV procedure design and execution. This in itself provides a safety benefit, and is the main driver for the introduction of P-RNAV procedures in Terminal Airspace. Considering P-RNAV as the appropriate requirement for Terminal Airspace RNAV operations, it becomes the enabler for RNAV operations in Terminal Airspace providing all the associated RNAV benefits.
2.2.9 The 1 NM level of navigation accuracy required for P-RNAV can be achieved using DME/DME, GPS or VOR/DME. It can also be maintained for short periods using IRS (the length of time that a particular IRS can be used to maintain P- RNAV accuracy without external update is determined at the time of certification and varies according to aircraft and equipment type).
2.2.10 The P-RNAV certification and operational approval criteria were developed with the intent of causing the least disruption and cost to the existing aircraft fleet. Many of the systems in use today are capable of track keeping accuracies far better than ± 1NM and the requirements were developed with the intent of satisfying the majority of the existing RNAV systems in order that full benefit can be derived from their features.
2.2.11 The P-RNAV concept offers the opportunity to provide harmonisation of standards, which should be encouraged and supported.
2.2.12 IFATCA policy states:
| “Where the introduction of Precision RNAV procedures entail closely spaced parallel tracks, suitable procedures should be established for the case of loss of navigational accuracy, taking into account such factors as ground equipment capability and controller training.” |
This policy remains valid. One of the main safety requirements highlighted in various studies is the need for the ability to be able to fall back to conventional procedures and techniques in the event of an RNAV system failure. Such a system failure can refer to a variety of equipment, such as airborne equipment upon individual aircraft to the failure of ground based equipment, such as DMEs, which are critical for a particular procedure. In either of these examples, failure of the equipment resulting in the loss of navigational accuracy would require intervention by the controller using conventional techniques.
2.2.13
| “Any introduction of Precision RNAV routes should ensure that these routes are spaced at such a distance from each other that the required separation minima are not likely to be infringed if an aircraft on one of the routes deviates from its cleared path.” |
The policy above continues to be valid. However, ICAO Annex 11 is now in accordance with IFATCA policy. This policy is therefore no longer required.
2.3 Approach
2.3.1 RNAV operations from the Final Approach Waypoint (FAWP) to the Missed Approach Point or Threshold require a very stringent set of criteria. P-RNAV is not considered as suitable for use on the final approach segment. RNP RNAV is being promoted as the industry standard for approach operations.
2.3.2 Details of RNP RNAV for the approach phase of flight can be found in agenda item B.5.11 or B.5.14.
Conclusions
3.1 The P-RNAV concept offers Terminal Airspace RNAV operations that are consistent on a global basis, based on a common set of design and operation principles, ensuring consistent levels of flight safety. This is in contrast to the recent situation, where variations in RNAV approval requirements, variations in procedure design and procedure publication / charting, and the variations in navigation data integrity, have been recognised to have adverse safety implications.
3.2 There are numerous varieties of RNAV in use at a multitude of locations around the world. Attempts have been made, and are continuing to be made, to introduce a degree of harmonization for RNAV standards. IFATCA supports the harmonization of RNAV standards and requirements.
3.3 The introduction of P-RNAV procedures around the world will require that policy be developed and reviewed on a regular basis to ensure that such procedures are introduced in a manner that will be beneficial to controllers.
3.4 IFATCA should actively participate in ongoing discussions about the use of P- RNAV and the formulation of policy regarding the use of P-RNAV procedures.
3.5 IFATCA policy should be developed to support the deployment of P-RNAV where operational and environmental benefits can be obtained. At present there is limited policy available for P-RNAV operations. Some of the existing policy continues to be valid. However, as P-RNAV is introduced on a more widespread basis, there will be a need to introduce new policy to ensure that P-RNAV routes and procedures are introduced in a standardised manner that will ultimately be beneficial to controllers.
3.6 There are no ICAO standards available for the deployment of P-RNAV procedures. This issue is perhaps the single largest problem stopping the widespread introduction of P-RNAV procedures. ICAO SARPS for use for P- RNAV need to be developed as a matter of priority.
Recommendations
It is recommended that:
4.1 IFATCA policy on page 3 2 3 10 in the IFATCA manual:
“Any introduction of Precision RNAV routes should ensure that these routes are spaced at such a distance from each other that the required separation minima are not likely to be infringed if an aircraft on one of the routes deviates from its cleared path”
be deleted.
References
IFATCA Christchurch 1993, WP88 – RNAV: Monitoring the Implementation.
IFATCA Ottawa 1994, WP91 – Amendment to Current Policy on RNAV Procedural Separation Minima.
IFATCA Ottawa 1994, WP99 – RNP for Approach and Landing.
ICAO Manual of RNAV Operations (Doc 9573).
ICAO Annex 11 – “Air Traffic Services”, 1994.
ICAO Doc. 9613-AN/937 Manual on Required Navigation Performance (RNP), First Edition – 1994.
ICAO PANS-RAC Doc 4444 – “Rules of the Air and Air Traffic Services”, 1985.
ICAO Doc 7030 – “Regional Supplementary Procedures”, 1987.
ICAO Doc 8168 – “Procedures for Air Traffic Services – Aircraft Operations (PANS-OPS).
EUROCONTROL Doc 003-93 – Area Navigation Equipment – Operational Requirements and Functional Requirements.
RTCA Do236/EUROCAE ED75 – Minimum Aviation System Performance Standards: Required Navigation Performance for Area Navigation, 1996.
JAA TGL-10 – Airworthiness and Operational Approval for Precision RNAV Operations in Designated European Airspace.
JAA TGL-10 – Frequently Asked Questions.
AC 120.29A – Approval Guidance for Approach and Landing.
Notice of Proposed Rulemaking for RNAV Routes.
PANS-RAC 1-4.
Last Update: September 29, 2020