Review of WC 10.2.11 – The Free Flight Concept

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Review of WC 10.2.11 – The Free Flight Concept

62ND ANNUAL CONFERENCE, Montego Bay, Jamaica, 8-12 May 2023

WP No. 162

Review of WC 10.2.11 – The Free Flight Concept

Presented by PLC



In 1999 a free flight concept policy was introduced at the International Federation of Air Traffic Controllers’ Association (IFATCA) Conference in Santiago, Chile. Although similar concepts and ideas were introduced and even became IFATCA policy, almost none of those policies which will be presented in the paper got implemented in the world. Free flight concept as presented in the IFATCA policy hasn’t developed into something useful or something that we can implement as is. This paper will review the policy and will argue if this policy should stay in the TPM or if it should be removed. The paper will also address similar policies and concepts pertaining to the free flight concept.


1.1. The free flight concept policy dates from 1999 and was never amended.

1.2. The free flight concept paper was accepted as an information paper, but following significant discussion at conference, the majority of the conclusions were adopted as Provisional Policy.

1.3. Provisional Policy defined at IFATCA 40th ANNUAL CONFERENCE, GENEVA 2001, WP 150, Report of the Executive Vice-President Professional as – Also adopted from the recommendation(s) in the relevant paper.

1.3.1. This is a policy which is thought, in the light of existing research and information, to be substantively correct, but which it is also considered may require significant amendment following a more developed study or as new information becomes available.

1.3.2. Provisional Policy should be the subject of positive action by Member Associations and can be presented by the federation’s representatives at international meetings as being “Provisional Policy”. This means that while it should normally form the basis of their position, they have discretion as to the degree to which the policy should be pressed depending on the prevailing circumstances. Provisional Policy is printed in a different font in the Manual to clearly indicate the fact that it is only provisional.

1.4. In the presented paper it was recommended that IFATCA will establish a joint task group with IFALPA to evaluate the “free flight concept” since the definition of Provisional Policy requires, such a task group was never established and no record of an attempt to establish one was found.

1.5. The reviewed policy never came to an implementable concept.

1.6. Over the years similar concepts such as FREE ROUTE AIRSPACE and different methods evolved without taking into consideration the “free flight concept”.

1.7. At the IFATCA 2022 Virtual Conference, the Professional and Legal Committee (PLC) and the Technical and Operations Committee (TOC) conducted an overhaul of the TPM and policy WC 10.2.11 was identified as needing to be reviewed.

1.8. This paper will examine if this concept is still valid, or if we have already covered this concept with other policies.


2.1. The “free flight concept” – to quote from the report of The Radio Technical Commission on Aeronautics (RTCA) Board of Directors select committee, on Free Flight (1995).

2.2. “FREE FLIGHT” is defined as:

A safe and efficient flight operating capability under instrument flight rules (IFR) in which the 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 unauthorized 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 toward free flight.

2.3. The “free flight concept” was a concept developed to take the place of the current air traffic management methods using technology. Full free flight reduces significantly the need for air traffic control (ATC) operators by transferring several responsibilities to the pilot in command. This gives the pilot the ability to change trajectory in mid-flight.

2.4. The “free flight concept” began as an effort to become less dependent on the human factor and more dependent on the growing technology of its day, using computer communication to ensure the required separation between aircraft.

2.5. A couple of the reasons for the development of the idea were the OPEC fuel crises and the Professional Air Traffic Controllers Organization (PATCO) strike of 1982 resulting in the firing of thousands of controllers by President Ronald Reagan. This showed how vulnerable air transportation was to economic forces.

2.6. These days true “free flight” applications exist only on a small scale in selected airspace operations where only the most well-equipped aircraft operate, such as at high altitude by commercial airliners. One example is the Johannesburg oceanic control which has an entry point and exit point, the pilot will file a flight plan in any route they want, and they have to stick to the route they filed, any deviation requires ATC clearance, the pilot also can’t change its altitude. Those “free flight” airspace concepts do not comply with the policy intent.

2.7. A number of similar concepts as Free Route Airspace (FRA), and Functional Blocks Airspace (FBA) give better solutions to the problem this paper is elaborating on. One example is the “Virtual Centres – Review ATS 3.15 Functional Blocks of Airspace” paper from 2017.

2.8. Free Route Airspace (FRA) (Source: EUROCONTROL ERNIP Part 1) is a specified airspace within which users may freely plan a route between a defined entry point and a defined exit point, with the possibility to route via intermediate (published or unpublished) significant points, without reference to the ATS route network, subject to airspace availability. Within this airspace, flights remain subject to air traffic control.

2.9. Even though technology has made incredible progress (systems today are very reliable) the “free flight concept” did not mature into something tangible as opposed to the Free Route Airspace.

2.10. Despite the technological leap this application of the “free flight concept” requires the use of the same technology or collaborating systems between aircraft since it is one of the main key elements for maintaining separation.

2.11. In “The ‘Free Flight Concept’ – Human Factors Considerations” paper from 1999 a crucial explanation was presented by Dr Charles Billings of Ohio State University, in his book “Aviation Automation – The Search for a Human- Centered Approach” argues that if the human remains responsible for safety, then the human must retain the authority with which to exercise that responsibility, by whatever means.

2.12. Automation must be a tool over which the human must have full authority. Since detecting conflicts for aircraft on random routes is more difficult than if the traffic were structured on airways, the controller will have to rely on the automated system to detect problems and provide resolutions that solve the problem.

2.13. Alerts may be given in situations where later information reveals that separation standards would not be violated (this is due to uncertainty in trajectory estimation). Therefore, alerts must be given when there is the possibility that separation may be violated, and the controller must consider all alerts as valid.

2.14. Dr Billings also notes, that if a controller accepts a computer decision and it turns out to be faulty, the controller is responsible. If the controller rejects a computer decision and substitutes one that is faulty, the controller is also responsible. This sort of dilemma represents a classic “no-win” solution for the controller.

2.15. The amount of traffic has increased significantly since the days when this paper was written, and different ways have been found to deal with capacity.

2.16. Over the years there has been impressive progress in managing the growing traffic and the tendency to approve direct routings, point-to-point or approved requested headings has ignificantly increased.

2.17. At present, controllers build up a “picture” of the traffic situation from various sources. In monitoring the traffic situation, they are considering what is actually happening and what is likely to happen. This is based on a great deal of confidence because the controller has “active” control over the traffic situation. Unless there are considerations established to maintain that active participation, far from having a “cooperative” relationship with the flight deck for the separation function, controllers will become “passive” monitors and will find themselves in a position where they are likely to “lose the picture”.

2.18. According to a NASA-initiated study from 2015 which suggests that monitoring tasks should be done by robots. The study paired NASA’s research psychologist, Steve Casner, with Jonathan Schooler, a professor at the University of California, Santa Barbara, to examine why monitoring failures happen even among experienced and highly trained airline pilots. Their results indicate that humans may be inherently bad at watching computers work – and we are unlikely to get any better, no matter how careful the selection or training.

2.19. “Our study really does suggest that vigilance is a very difficult task for people,” said Schooler. “Extended uninterrupted monitoring can be draining. The antidote to that is interruptions that break up the monotony, but we also found that the interruptions themselves contributed to lapses,” said Schooler.

2.20. “And people will spontaneously mind-wander, and that can also contribute to monitoring difficulties,” all in all, the researchers found, pilots missed 25 per cent of all altitude crossings they were charged with monitoring. “This task of watching a computer system while it works is incredibly trying, if not impossible, for a human to do well,” Casner said.

2.21. In a paper presented at the Human Factors and Ergonomics Society 41st Annual Meeting in 1997, it was suggested that “Free Flight” could cause significant new demands on a controllers’ workload, while at the same time degrading their situation awareness.

The paper concluded:

“…In addition, the predictability of aircraft movement will likely decrease under free flight. In today’s system, controllers gain information about how aircraft are going to behave from knowledge of assigned flight paths and destinations. There are a limited number of ways that aircraft will proceed through a given airspace.

Today, the controller can usually detect deviations from these norms. With free flight, aircraft may come from almost any direction into a sector, change paths without controller action or approval, and depart the sector in almost any direction. With this loss of aircraft predictability, the controller will not be able to project ahead to determine potential separation problems.

Projecting the future actions of aircraft (the highest form of situation awareness) is critical to the controller’s responsibility to make timely control actions. Thus, there is a concern as to the controller’s ability to understand the significance of aircraft actions and adequately predict impending problems in order to be able to manage traffic effectively”.

2.22. Several issues that remain unanswered and must be addressed are:

2.22.1. What should be done in an emergency “Is the ATCO expected to just jump into an uncontrolled situation and rescue the day?”

2.22.2. Weather avoidance and sudden decisions to change the route without ATCO ‘s approval or permission.

2.22.3. Equipment malfunction in the middle of “free flight” airspace (the aircraft will be flying blind).

2.22.4. Busy cockpit, who is responsible for separating the aircraft and are they able to take this responsibility?

2.23. IFATCA Provisional Policy is:



The situational awareness of the controller shall be a key element to enable that controller to maintain active monitoring of flights conducted in “Free Flight Airspace” and to enable them to interact co-operatively with aircrew.


2.26. This policy is stating the obvious, no need to describe our everyday job.


Due to the unpredictable nature of aircraft manoeuvres in “Free Flight Airspace”, the responsibility for conflict detection and resolution, and the maintenance of the safe separation function, should rest with the pilot in command of that flight.


2.28. Stating the obvious, if the pilot flies on his/her own headings ATCO can’t and shall not be responsible for the pilot’s actions. This basically means that the pilot will do the ATCOs job with no training or proper qualifications.


Procedures shall be established to safely integrate any aircraft into a “Managed Airspace” environment when no longer able to meet the requirements of the “Free Flight Concept”.


2.30. Free Route Airspace covers this paragraph.


Clear guidelines and procedures shall be established to resolve any differences of aircraft and ATC conflict alerting systems and the reactions that pilots and controllers will be required to take when conflict alerts are indicated.


2.32. Covered by IFATCA policy ATS 3.33 – Relay of Flight Information from Air Traffic Service To Aircraft,

IFATCA encourages the development of technologies to automate the provision of Flight Information Service.

When flight information is provided through automatic data transmission systems, clear procedures shall be established, and the allocation of tasks and responsibilities shall be clearly determined.



The question of de-skilling of ATC personnel shall be considered when effectively delegating conflict alert and resolution action to automated systems.


2.34. Covered by Transfer of Separation Functions to Pilots – Human Factors Aspects, WP 154 38th ANNUAL CONFERENCE, Santiago, Chile 1999:

“If separation functions are transferred to the cockpit the situation awareness and skills base of the ATCO will be degraded to the point when intervention will not be possible.”

2.35. The importance of a human-centred approach to the “Free Flight Concept” should be a priority and one that recognises the limitations of both human and automated systems and the interaction that results.

2.36. Covered by Transfer of Separation Functions to Pilots – Human Factors Aspects, WP 154 38th ANNUAL CONFERENCE, Santiago, Chile 1999:

“Aircrew workload will increase by fulfilling additional tasks, which are currently carried out by ATC. This might lead to overload situations in cockpit workload when other, higher priority, tasks have to be taken care of by the crew.”

2.37. It cannot be assumed that ground-based, human-centred systems (Air Traffic Control) can simply take over the responsibility for the control and separation assurance of flights operating within Free Flight Airspace in the event of a failure of airborne systems. The limits of human-centred control shall be clearly established when considering ATC as a back-up to the “Free Flight Concept”. This is especially important when considering significant airspace capacity increases using the “Free Flight Concept”.

2.38. Eurocontrol in the Free Route Airspace protocol and As Network Manager, provide support to ANSPs in the form of airspace design, the concept of operations, advice on aeronautical publication and the pre-validation of each new FRA environment to ensure that airspace users are able to plan flights in line with the concept.


Ground-based conflict alert systems and ASAS shall be proven in all circumstances before the “Free Flight Concept” is adopted.


2.40. Covered by Surveillance Application Policy – ASAS WP No.93 46th ANNUAL CONFERENCE Istanbul, Turkey 2007:

“Before ASAS applications are put in place it should be proven that they maintain or improve system safety while providing net cost benefits.”


The dispersion of workload from the ground to the cockpit needs to be reviewed carefully. The “Free Flight Concept” appears to accept that the transfer of responsibility for separation and associated workload can be safely accommodated by aircrew.


2.42. Free Route Airspace covers that paragraph, and even more since ICAO studies also show a slight decrease in controllers’ workload as a result of free route airspace implementation, mainly coming from a decrease in radio transmissions, monitoring and coordination tasks. In addition, IFATCA TPM (2022), LM 7.1.3 – Transfer of Control Functions – Legal Aspects.

States shall have in place regulations detailing procedures to be followed before Separation assurance can be transferred to the cockpit.

The Initial and final points at which Separation Assurance are transferred from ATC to the pilot shall be accurately defined in all cases.

The responsibility for providing separation between the intercepting aircraft and all other aircraft shall be clearly defined. ATCOs should not be held liable for incidents or accidents resulting from an interception.


2.43. Consideration should be given to the establishment of suitable qualifications for aircrew operating in Free Flight airspace. The term “EFR” already seems to be accepted as a suitable acronym for “Electronic Flight Rules”.

2.44. Not an acceptable acronym or known.


3.1.  The original policy never became something applicable even after 23 years.

3.2.  As time went on, similar and better concepts such as FAB and FRA developed into applicable working methods.


4.1. It is recommended that WC 10.2.11 THE “FREE FLIGHT CONCEPT” HUMAN FACTORS CONSIDERATIONS is deleted as provisional policy from the IFATCA TPM.


IFATCA Technical and Professional Manual, Version 6.5 2022, Montreal, Canada: IFATCA.

IFATCA 40th Annual Conference Geneva 2001, working paper 150 “Report of the Executive Vice-President Professional”.

RTCA: Board of Directors’ Select Committee on Free Flight (1995).

Mogford and Earl Stein, Proceedings of Human Factors and Ergonomic Society 41st Annual Meeting.

Aviation Automation: The Search for a Human-Centered Approach. 1997. Charles E Billings.

Situational Awareness in ATC – a Model, Bert Ruitenberg, IFATCA Human Factors Specialist, The Controller Magazine, Volume 36, 1st Quarter 1997.

International Symposium on Aviation Psychology, Columbus, Ohio, April 1997 (reprinted in Controller magazine edition 3/97).

The Future of ATC – Human Factors and Automation, Panel on Human Factors in ATC Automation, National Research Council, 1998.

Final report of the RTCA Task Force 3, Free Flight Implementation. RTCA, Inc., Washington, DC, Oct 26, 1995.

IFATCA. (1999). Working paper 161 The “FREE FLIGHT CONCEPT” – Human factors considerations.

Humans bad at monitoring tasks required of pilots | Business Standard News (

Last Update: September 26, 2023  

September 17, 2023   122   Jean-Francois Lepage    2023    

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