At the 31st. IFATCA Conference in Bournemouth SC 1 was given the task of continuing to monitor the application of RNAV and, additionally, to investigate the aspects of policy of implementation which need to be addressed from an ATC viewpoint.

Last years WP 75 on this subject described and defined the 2 levels of RNAV capability – Basic and Precision and it is considered unnecessary to repeat those definitions in this paper.

As Basic RNAV capability compares with the standards achieved by conventional VOR or DME equipped aircraft, it is considered that initially its more widespread application will probably be the use of RNAV equipment within a defined ATS route structure. This should cause no major difficulties to ATC. It is possible that routes could be established across regions which have been unable to support ground-based aids. However, such routes would necessarily be restricted to aircraft fitted with appropriate equipment. It will therefore be necessary for controllers to be aware of the navigational capability of aircraft under their control. This information will be required on the flight plan and will be relayed to the controller in a suitable format. In some countries this already happens. In some areas, where traffic density is light, it should be possible to establish RNAV routes without radar surveillance or Automatic Dependent Surveillance (ADS). Only where Basic RNAV is used for direct routeing – outside the established route network – is it likely that new procedures and associated training will be required.

Precision RNAV, with its much more accurate navigational capabilities, requires more detailed procedures to ensure that such capabilities can be used safely, and to the advantage of airlines and ATC. Adequate training for controllers must be provided.

In many parts of the world, where the use of Precision RNAV could make a significant contribution to an increase in capacity, it will be of the utmost importance that different manufacturer’s equipment produce the same end results with regard to turn performance, etc. The aircraft’s interpretation must be homogenous within the system as a whole.

The increase in system capacity mentioned above will be achieved only by reducing current separation standards. The question arises, “What happens in areas where aircraft change from current separation standards to the new reduced distances?” It would seem sensible to establish transition areas where changes can be managed, both in the entry and exit phases.

When aircraft are operating closer together, any deviation – either laterally or vertically assumes much greater importance. The “Future European Air Traffic Systems” (FEATS) group suggested in its report that RNAV routes should not be so close together that monitoring deviations becomes a problem. However, the question still has to be asked, “Are ATC radar’s accurate enough to monitor deviations in time to take remedial action?” should it become necessary. Perhaps the answer lies in automation; should the system be capable of monitoring itself to detect deviations from the cleared route, and alert the controller to such events in sufficient time for remedial action to be taken? However, it could be argued that, in the first instance, any warning should be generated on the flight deck to indicate to the crew that the aircraft is deviating from the required flight profile. This would leave the navigation on the flight deck where it properly belongs. The problem described in para. 2.5 would remain if such an airborne warning failed to operate.

There is a direct comparison here between Precision RNAV and advanced MLS procedures. Disregarding, for the moment, problems such as vortex wake separation standards a question of philosophy arises. This is whether or not aircraft which have a capability to fly a very accurate flight profile should need to be vectored by controllers at all. This question will need to be answered as it is fundamental to the development of procedures based on the use of Precision RNAV, although it is probable that before such an advanced air traffic system is available an interim stage, stages, will be necessary.

As far as implementation of RNAV routes is concerned, no MA’s have indicated that problems have arisen in their country as a result of implementation of, or development of already established RNAV routes during the last year.

Within Europe, the ICAO European Air Navigation Planning Group (EANPG) confirmed in 1990 the urgent need for an evolutionary development of RNAV installation and operations throughout the European Region.

The scope of the “Strategy for Implementation” in the EUR Region covers:

a) an agreed timetable for implementation;

b) operational applications;

c) RNAV operating procedures;

d) airborne systems;

e) reference systems;

f) approval of RNAV operations/systems;

g) training requirements;

h) ATC systems.

The main objectives of the implementation strategy are:

a) by January 1, 1993, States are to complete and publish legislation on RNAV equipment certification and operational approval;

b) from 1995 onwards, States are encouraged to establish random RNAV areas where appropriate;

c) By 1998 States are to complete the optimisation of ATS routes and procedures to meet the mandatory carriage of RNAV equipment within the notified airspace.

The target dates set out above have been recognised by civil aviation providers and users of the EUR region as a pre-requisite to any significant improvement of the air traffic management system in Europe.

Full details of the strategy for the implementation are set out in the 4th edition of ICAO EUR Doc. 001, RNAV/4, published in 1992.

To Conclude

Work continues internationally to bring the benefits of RNAV operations into use. Many countries now offer RNAV routes as part of their ATS structure, and some make use of aircraft’s’ Precision RNAV capabilities and/or offer random RNAV routeings.

Where such operations are permitted, controllers must be informed of the aircraft’s’ navigational performance capability.

Consideration will need to be given to the method(s) by which aircraft enter and leave areas of current standard separation when taking advantage of reduced separation possible with RNAV.

In the case of random RNAV routes, ATS systems should be capable of processing flight plan data concerning random RNAV routeings. Air traffic controllers should be able to amend/update the relevant information in the computer system.

Prediction and display of potential conflicts should be provided at the planning stage.

Short term conflict alert and assistance with conflict resolution should be provided on radar displays.

Random RNAV routeing may require the ability to display predicted tracks so that crossing points of sector or FIR boundaries can be anticipated.

Where Precision RNAV is used to introduce closely spaced parallel ATS routes, controllers should be given additional training and adequate procedures should be established for the case of loss of navigational accuracy by aircraft. Training will also be required where random RNAV routeings are introduced – such as RT phraseology, co-ordination procedures, or identifying conflicts which could occur anywhere in the airspace.

Where RNAV is used to define SID’s/STAR’s/holding or approach procedures, controllers should be given specific training to exploit these navigation capabilities.

It is recommended that

Controllers should be presented with information, by any suitable means, concerning navigational capability of aircraft under their control.

In airspace where random RNAV routeings are permitted, the ATS system should be capable of processing random RNAV plans and controllers should be able to amen/update such information.

Track prediction vectors should be available on radar displays used to control airspace where random RNAV procedures are permitted.

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.

Adequate training must be provided for controllers managing RNAV operations – such items as RT phraseology, co-ordination procedures and conflict identification need to be considered.

IFATCA should ensure that controllers’ expertise is used in the deliberations taking place to provide appropriate specifications for the use of RNAV.