Investigate a Possible Future Air Traffic Management Concept

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Investigate a Possible Future Air Traffic Management Concept

35TH ANNUAL CONFERENCE, Tunis, Tunisia, 15-19 April 1996

WP No. 95

Investigate a Possible Future Air Traffic Management Concept


The purpose of this paper is to investigate a possible future Air Traffic management concept and its implications for Air Traffic Controllers.

Current separation standards are based on fixed tolerances that are necessarily worst case conditions. With the evolution of CNS/ATM systems, we are seeing a degree of automation of the communications and ATC functions that will allow this constraint to be removed.

The concept under investigation recognises the fact that the provision of a separation service by ATC depends on a controllers real time information about an aircraft’s position and intent, and the degree of confidence that can be placed on the accuracy of that information. In essence, there is always a “Volume of Uncertainty” surrounding an aircraft’s position that must be considered by the ATC system in maintaining separation with other traffic.

The size of this volume depends on each of the system elements of the CNS/ATM concept, and is likely to remain a dynamic variable. It is also likely that, to obtain maximum efficiency, it will be necessary to recognise and accommodate this variability in airspace design and management methodologies of the near future.

The most fundamental shortcoming of the present airspace system is inflexibility. This in part is caused by segmented airspace, differing standards, political and military considerations and many other related reasons, that are not related to traffic needs.

Future ATM systems will be on high speed data links handling all routine aeronautical communications, with position information being derived from ADS and other “real Time” tracking systems. Future aircraft navigational capabilities will be based on highly accurate satellite signals with space, or ground augmentation as necessary.

To successfully utilise these advanced systems in an efficient manner will require less stringent traffic management rules and techniques, with a more dynamic approach required to each circumstance.

For this to succeed , a global system of standardised equipment and consistent procedures needs to be developed.

This evolutionary process will result in a shift from “Air Traffic Control” to “Air Traffic Management”, with controllers intervening in aircraft trajectories only when necessary.

Basic functionality for the application of dynamic separation standards are already in place in some parts of the world, with automated systems designed to use the actual navigational capabilities of individual aircraft.

The functional specifications for any dynamic separation standard (DSS) development should incorporate the basic functionality to develop and trial DSS concepts using actual navigation capabilities of aircraft, whether FANS equipped or not.

This is achieved by alerting controllers to changes in aircraft navigation ability (RNP required Navigation Performance, FOM , Figure of Merit), cueing changes in display parameters associated with conflict assessment tools, such as tolerance boxes ( providing graphic display of protected volume of airspace) and route leader lines.

Graphic display concepts support existing standards as well as those under development for use in a mixed RNP environment. As this concept matures, controllers will be able to graphically display protected volumes of airspace for both RNP and ANP (Actual Navigation Performance), currently reported as FOM.

Protected volumes equate to the navigation tolerances applicable to each aircraft, as used in the existing separation standards.

Typically, the navigational capability of existing RNAV equipment equates to a circle of protected airspace with a radii of between 30 and 50 nm (Currently under discussion) , which would be displayed as elongated oval shape tolerance area centred on the actual aircraft position computed by the automated system, based on extrapolation from the latest position report. By invoking a look ahead or fast forward function, while the tolerance boxes are displayed, future conflicts may be graphically assessed. Level filtering, when invoked during conflict assessment will act to reduce display clutter. Changes to tolerance boxes (RNP) would then show the effect of changes in conflict.

Changing Environments

Possible areas of environment change that would result in differing standards being applied would include :

  • IMC/VMC;
  • RNP/FOM (ANP);
  • Free Flight;
  • Weight Classification.

Free Flight Concept

A recent (January 95) report by the US RTCA Select Committee on Free Flight defined Free Flight as:

“A safe and efficient flight operating under IFR in which operators have the freedom to select their path and speed in real time. Air traffic restrictions are only imposed to ensure separation, to preclude exceeding airport capacity, to prevent unauthorised flight through special use airspace, and to ensure safety of flight. Restrictions are limited in extent and duration to correct the identified problem. Any activity which removes restrictions represents a move towards free flight”.


The key to free flight is the automation of the ATM system, with the primary tool being the Conflict Probe. This probe will monitor the proposed trajectories and assess any conflict between the alert zones of traffic within designated airspace.

Resolution of conflict will be achieved by the changes to separation standard being applied or reversion to aircraft being assigned linear positions on separated tracks, as they are today.

Factors affecting an aircraft’s ability to conform with a differing separation standard include its’ navigation system ( standard hardware) and communication ability (data link capability), while pilots status (training) will also be a contributing factor.


With a change to the prime arbiter of the proposed flight trajectory shifting from the ground to the cockpit, consideration must be given to the need for situational awareness in the cockpit in the form on an in flight situational display, allowing the pilot to be more involved in the course of action required to resolve a conflict situation.

Future Work

Future work on this subject will need to consider a range of important related issues including

International acceptance that Dynamic Separation Standards should be established by ICAO and implemented on a global basis.

Military Integration – a better integration of military operations and airspace requirements is another ideal that will be difficult to achieve.

Human Factors – A growing but very much inexact science with critical application in the area of ATC automation.

Program Integration (CNS/ATM, ADS) – A carefully planned integration policy needs to be developed so that a harmonious inception policy is established and adhered to.

Transition Procedures – Dynamic separation standard development, and their method of use, may be one way to approach the difficult question of transition between conventional ATM and CNS/ATM.

Minimum Equipage (ground/airborne) – The question of aircraft certification does not greatly concern ATC, however we are greatly concerned if certification standards diverge to the extent that our function is complicated excessively. Ground equipment should be designed to take full advantage of the airborne system ability to provide vital information to an efficient ATM system.

Controller Authority – Who retains control? It is in the controllers interest, and that of the travelling public, that control over any ATM system remains centralised and on the ground.

Separation Standards – Development of reducing separation standards , resulting from new technology, needs to be carefully considered, with accurate testing in conjunction with acceptable target levels of safety.

Limitations – Largely a transitional issue, but we are already starting to see airspace priority being demanded by operators who have made considerable investment in new CNS/ATM technology. This situation has the potential to cause significant problems for controllers.

Use of improved dynamic separation standards would allow the provision of a ATM system able to accommodate the traffic demand, make more efficient use of airspace and airport capacity, and permit the harmonious treatment of flight transiting all airspace, all in a more cost effective and uniform manner.

The use of DSS may be seen as an important tool in the accommodation of user preferred three dimensional and four dimensional flight trajectories.

DSS have a potential to provide significant cost optimisation for the airlines and the provision of ATS generally.

The utilisation of this concept would present a significant change in the way ATC’s perform their task. This paper in no way seeks to champion the concept. Its primary purpose is to stimulate discussion with a view to developing a pro-active and co-ordinated approach to the evolution of ATM systems.

This paper should be the basis for continued research.

Last Update: September 28, 2020  

February 12, 2020   212   Jean-Francois Lepage    1996    

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