38TH ANNUAL CONFERENCE, Santiago, Chile, 15-19 March 1999
WP No. 161
The “Free Flight Concept” – Human Factors Considerations
Prompted by concerns that the present system of enroute control of air traffic was inflexible and in the belief that there were potential economic benefits if more flexible routes can be approved, airline management and their representative organisations, ATA and IATA, have considered some fundamental changes in air traffic management.
They have proposed a “Free Flight Concept”, in which operators would have the freedom to determine aeroplane trajectories and speeds in real time (IATA, 1994; RTCA, 1995).
Relevant parts of the RTCA (The Radio Technical Commission on Aeronautics (RTCA) is a non-profit organisation sponsored largely by the FAA. It proposes standards for technology and its uses in the national aviation system) document are included in this working paper.
The subject of “Free Flight” was placed on the work programme of SC4 at the Toulouse Conference in 1998. It was requested that the Human Factors aspects of this concept were identified,albeitthatthefullproceduresforthe”Concept”hadnotbeenfullyestablished. Tothis end, Chairman SC4 and Executive Vice President Professional have discussed this matter with a view to providing an initial Working Paper for this Conference.
SC1 has presented an Information paper on “Free Flight” at the Taipei Conference – WP93/1997.
The “Free Flight Concept”
To quote from the Report of the RTCA, Board of Directors’ Select Committee, on Free Flight (1995), “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.
The RTCA document suggests that the “Free Flight Concept” can provide the needed flexibility and capacity for the foreseeable future (approximately the next 50 years). At its basis, the concept enables optimum (dynamic) flight paths for all airspace users through the application of communications, navigation, and surveillance and air traffic management (CNS/ATM) technologies and the establishment of air traffic management procedures that maximise flexibility while assuring positive separation of aircraft.
The primary difference between today’s direct route clearance and “Free Flight” will be the pilot’s ability to operate the flight without specific route, speed or altitude clearances. Restricting the flexibility of the pilot will only be necessary when:
a) potential manoeuvres may interfere with other aircraft operations [or] special use airspace;
b) traffic density at busy airports or in congested airspace precludes “Free Flight” operations;
c) unauthorised entry of a special use airspace is imminent; or
d) safety of flight restrictions are considered necessary by the air traffic controllers.
This “Concept” has already been adopted in other parts of the world, e.g. The Eurocontrol Operational Control Document (OCD) 1998. However, it is envisaged that the major objective of the “Free Flight Concept” – that is, high levels of flexibility in flying the aircraft – will still be constrained by traffic density.
The freedom for aircraft operators to operate an aircraft in the most flexible way possible does not necessarily mean “direct routing” – that is a flight straight from point “A” to point “B”. Because of the varying wind effects at altitude, it is more likely that operators will decide to adopt the most fuel-efficient route. This is generally referred to as “Optimum Flight Path” or “Minimal Time Track”. Rather than focus on specific track keeping, it is highly likely that specific tracks that take into account the most favoured upper wind component will be followed.
Another major requirement to accommodate the “Free Flight Concept” will be to re-designate existing airspace. In order to encompass the parameters of Free Flight, it is proposed that “Free Flight Airspace” will be established.
Only aircraft operating under “Free Flight” will be able to use this airspace. Other airspace directly under the control of ATC will be re-named “Managed Airspace” and uncontrolled airspace will simply be designated “Unmanaged Airspace”.
Regardless of the type or name of the airspace. It is clear that in order to contain the flexible free routing of aircraft under the “Free Flight Concept”, designated areas of airspace will have to be set aside purely for these flights to operate in. At first, it is expected that only the upper levels of airspace will be designated for “Free Flights”. However, the long-term goal is to be able to provide the “Free Flight Concept” from runway end to runway end, including movement within the Terminal Control areas. This is often referred to as “Gate to Gate”.
Another obvious factor, in the short term, will be the method by which “Free Flights” integrate to and from “Managed Airspace”. It is considered that designated “Entry/Exit Points” will have to be established to enable the safe and efficient transition of aircraft. A form of “Flow Control” is likely to still be needed in order to meet the requirements of the “Gate to Gate” philosophy and to safely match movements of aircraft into existing runway availability and occupancy times.
In the “Free Flight Concept”, a flight plan will be available to the air traffic service provider as a basis for flow management. It is possible, and highly desirable, to shift from a concept of strategic (flight path based) separation to one of tactical (position and velocity vector based) separation. There even may be instances included in the system’s design where separation assurance shifts to the cockpit. When this occurs, there will be clearly defined responsibility (pilot or controller) for traffic separation.
One realisation of “Free Flight” depends on the construction (by ground and/or aircraft computers) of protected and alert zones around each aircraft in the system. Position and short- term intent information is provided to the air traffic service provider who performs separation monitoring and prediction functions. The air traffic service provider may be required to intervene to resolve any detected conflicts. Short-term restrictions are used only when two or more aircraft are in contention for the same airspace. In normal situations, aircraft manoeuvring is unrestricted. It is intended that separation assurance will be enhanced by appropriate on-board systems, but TCAS will remain an independent safety net. This system will probably be defined under the generic term of an Airborne Separation Assurance System (ASAS). The flight paths will be projected to determine if the minimum required separation can be achieved. If the projection shows the minimum required separation cannot be maintained, then the conflict resolution software will suggest an appropriate manoeuvre.
It is also intended that flight crews will use Cockpit Display of Traffic Information (CDTI) equipment to assist them for:
a) situation awareness and traffic monitoring, and
b) co-operative ATC manoeuvres for specific applications.
It is suggested that the flight crew’s situation awareness will be enhanced with the use of CDTI and to aid them in the search, acquisition and identification of a specified aircraft, or in the understanding and monitoring of the local traffic situation and to monitor the progress of the flight.
It is intended that the controller will be involved to agree with the resolution necessary to avoid conflict and these instructions will be passed to the aircraft involved. The automation and the controller then verify the required separation is assured.
Although our understanding of the cause of human errors has progressed considerably, there is no doubt that many in air traffic control look to automation as the principal way to improve ATC safety, reliability, efficiency and airspace capacity. Although system designers predicate automation on human-centred principles, it will be necessary to make a compelling case for keeping the human controller in effective command of the system once advanced ATC automation is available. The point has to be made about “effective command” because there seems little question about the controller’s continuing responsibility for traffic separation regardless of the amount of automation interposed between the controller and his traffic. The suggestion that the pilot reacts to a conflict alert and then verifies the action to be taken with the controller, seems flawed, unless the controller has a similar display and traffic projection to work to in order for agreement to be reached to ensure separation is maintained. However, the “Free Flight Concept” will enable a situation to exist where no verification with the controller is required.
It also has to be accepted that the “Free Flight Concept” is likely to enable far greater flexibility and capacity in a given airspace. To expect the human to just take over and “pick up the pieces” when something goes wrong will no longer be an appropriate or safe alternative. Serious consideration has to be applied to the role of the air traffic controller in the “Free Flight Concept”. Unless significant upgrades in technology are provided to the controller, that mirrors and supplements the airborne conflict prediction and separation assurance systems, it cannot be assumed that ATC can be both effective and “co-operative” in assisting the pilot to avoid airborne collision in the “Free Flight Concept”.
The move to improve situation awareness on the flight deck, using CDTI, has already made the pointthat”co-operativeATCmanoeuvresforspecificapplications”canbeachieved. Whereas, this may refer to enhancing the relationship between ATC and the flight deck to assist in the separation function, does it also make the point that aircrew could actually take full responsibility for the separation function if they use CDTI data ?
In the “Free Flight Concept”, it is suggested that the “Responsibility for the safe operation of aircraft remains with the pilot in command.” and that the “Responsibility for separation between controlled aircraft remains with the controller.” But, in “Free Flight” we will have the situation where the immediate intentions of aircraft are basically unknown, as aircraft are given the freedom to operate exactly as they wish, on whatever trajectory and flight level they choose. Therefore, as far as ATC are concerned, “Free Flight” is certainly not a “controlled flight” in “controlled airspace” as we presently know it.
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.
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 to provide resolutions that solve the problem. 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 maybe violated, and the controller must consider all alerts as valid.
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.
The question of de-skilling is also raised with the “Free Flight Concept”. As automated systems take over the key role of conflict alerting, and over a greater projected time interval than a controller presently considers, then the controller who issues a machine-recommended clearance may not be able to assess retrospectively whether that choice was correct, for the outcome of that clearance will often occur in a sector not under his control and not visible to him. The alternative, of course, is to revert to short-term controller-initiated conflict avoidance, as occurs routinely in the present system.
The “Free Flight Concept” envisions that flight paths would be selected by pilots, or more likely dispatchers working in air carrier operations centres (AOCs), and implemented by the pilots with notification to, but without a requirement for concurrence by, the air traffic management system. This concept envisions the entry of a third, more or less equal, authority into the control process—the AOC—and it thus raises many questions about diffusion of authority and responsibility for air traffic movements. The air traffic management subsystem would be relegated to an oversight role unless a conflict was detected. It appears that the ATM system would function in somewhat the way that airborne collision avoidance systems now function: by using aircraft data and extrapolated trajectories to develop time, or distance-based, separation zones around aircraft, which are used to determine a need for alerting or conflict resolution in real time.
These uncertainties would pose problems for controllers (and for the ATM system) similar to but more acute than those they now face when TCAS issues a resolution advisory to pilots, who respond prior to notifying ATC that they are doing so. Yet controllers are expected to intervene, or supervise the computer that will intervene, on a “by exception” basis, only when there is a high probability of conflict. The likelihood that controllers will be able to detect and diagnose probable conflicts under a high level of uncertainty is low, and the proposal recognises this by stating that computers will accomplish this task and suggest appropriate resolution tactics.
The computer, of course, will also have periods of uncertainty during aircraft manoeuvres, before it is able to re-establish a stable trajectory prediction and project it forward in time to evaluate whether the manoeuvre has created a potential conflict. Yet the IATA (1994) proposal also states that the purpose of automation is to assist humans and not to replace human reasoning.
Regarding human factors, the RTCA (1995) report says only that “technology will not replace humans or replace their reasoning process but will allow them to do their job better”. The compressed times within which the humans would have to apply such reasoning and take action, perhaps given only retrospective notification of aircraft manoeuvres, appear to have received rather less attention than they deserve in the development of the concept.
The “Free Flight Concept” does not explicitly mention significant additional requirements on pilots. Nonetheless, the lack of “assured separation” that is provided by the present, admittedly cumbersome system would actually require higher cockpit vigilance with increased workload on aircrew to identify and resolve perceived and actual flight conflicts. With so many aircraft operating on a random basis, in relatively ‘open’ skies and with little ATC interaction, it will effectively be the aircrew who will assume the initial ‘burden’ of separation, albeit inside “controlled airspace”, managed and “controlled” by an ATC Authority.
Given that the workload of pilots is likely to increase substantially, maintaining vigilance with their airborne separation assurance systems and to ensure conflict resolution compliance, and, given the nature of their existing workload, especially in busy terminal areas, it may be necessary to establish new qualifications for dealing with this new “electronic” environment. The term “EFR” – for Electronic Flight Rules – has already been suggested to reflect the new operating techniques and environment that aircrew will find themselves in. Given the existing requirements for IFR flight, it follows that suitable qualifications should be adopted by those pilots prepared to operate in “Free Flight Airspace” and to prove their ability to meet the demands and responsibilities that operating in this new airspace environment will force upon them.
There is also a suggestion that changes to flight paths, effectively revising the routes and trajectories of aircraft already in the air can be accomplished from airline operations rooms using data-link. This has additional concerns for aircrew and controllers alike. Especially with regard to monitoring and situational awareness of what the aircraft is now “planned” to do. With the greater use of computers to judge and balance environmental and aircraft operating factors, the likelihood and temptation to “tinker” with existing “Free Flight” routes may become a standard operating procedure for airline operations staff. Effectively, “control” over the flight will be delegated to the Airline Operations room with aircrew and controllers attempting to deal with the enroute crisis of conflict alert and resolution. What then, if in the middle of a conflict resolution, the Airline Operations room feeds in a revised routing ? Who has control – who has responsibility ?
We therefore enter a “nightmare” scenario. It appears that little thought has been given to whether humans can operate and manage such a complex system. Rather, new technology will operate the system and humans will supervise its operation, but not necessarily with advance knowledge of how it is going to behave.
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 “co-operative” 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”.
The term “situation awareness” needs clarifying at this point. Knowing what is going on at a particular time can provide situation awareness. But, this does not necessarily mean that you will have situation awareness in 5 minutes time. When a controller has the “picture”, he is taking into account what is happening now and what is anticipated ahead. Therefore, any use of the term “situation awareness” must be accompanied by a clear definition as to what particular “situation” anyone involved, is actually aware of.
Dr Mica Endsley, Texas University, defined “situation awareness” as:
“the perception of the elements in the environment within a volume of time and space, the comprehension of their meaning, and the projection of their status in the near future”.
Our own Human Factors Specialist, Bert Ruitenberg, has described how situation awareness applies to the task of an air traffic controller. This was printed in Volume 36 of “the Controller” magazine. Some 11 elements of information sourcing contribute to a controller’s situation awareness. One of the most significant is the “picture”, the overview of the traffic situation, its development, its patterns and its flow. In recognising the ability of a controller to establish and maintain his own situation awareness, it is imperative that he remains an active participant in the process of “controlling” the air traffic situation, in order that he can continue to be resourced by these essential 11 elements.
In a paper presented to the 9th International Symposium on Aviation Psychology in 1997, Smith et al suggested that the key area of co-operative ATC management of Free Flight airspace by controllers would be the availability of “intent information”. In other words, clear indications of what different aircraft were going to do is essential for the controller to interact with the system and provide a co-operative response. Not only is this information absolutely necessary for the controller to make suitable airspace management decisions, it is obviously necessary to provide a co-operative response to aircrew for conflict detection and resolution.
It was also suggested that the handling of such information would be very complex, especially with the transmission and interpretation of such varying data.
Without the availability of “intent information”, the “Free Flight Concept” would be unworkable from an ATC point of view.
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 may 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”.
Regrettably, the question of maintaining safe control over the “Free Flight” airspace in these circumstances was not evaluated or challenged.
As proposed, the airborne systems may not inform the ATM system of their intent in advance; the ATM system and its supervisory controllers will not predictably be involved in air traffic movements, and may not have advance knowledge of any individual aircraft’s future trajectory. For these reasons among others, the likelihood that pilots and controllers will be able to remain in command of such a system is very low, for the system will not be predictable. The likelihood that those humans will not be held accountable for the results, however, is negligible.
Wiener (1993) pointed out (with respect to aircraft automation) that “Many in the aviation industry have assumed that automation would remove human error, replacing the fallible human with unerring devices. The research of Wiener and Curry suggests that this may be overly optimistic, and that automation merely changes the nature of error, and possibly increases the severity of its consequences.”
In an earlier paper (1987) Wiener said, “The experience from commercial aviation shows that it is unwise to dream of automating human fallibility out of a system. Automation essentially relocates and changes the nature and consequences of human error, rather than removing it, and, on balance, the human operator provides an irreplaceable check on the system. The search should be directed toward the management of human caprice, not the elimination of its source”.
There is no reason to believe that automation in air traffic control and management will be a panacea, any more than it has been in the cockpit. Any tool, including automation, shapes human behaviour. The human errors expected in a highly automated system would be expected to be different, and indeed they are different. But automation does not, and cannot, eliminate human error (although if properly designed, it can sometimes mitigate the consequences of human error).
Automation, of course, is not infallible either. The literature abounds with failures of automation to perform as expected. These failures are among the reasons why humans must be an integral part of the system. They are there to compensate for the imperfections of the automation. They are also there, as noted earlier, to accept responsibility for system safety. If they are to remain in command, they must be involved in system operation. Not only when the automation fails, but during normal operations as well, in order to be in the loop when the inevitable failures occur. The human operator is the final line of defence in automated systems, and the new systems proposed for air traffic management, such as the “Free Flight Concept” are no exception. Existing IFATCA Policy on the use of automation is as follows:
“Automation must improve and enhance the data exchange for controllers. Automated systems must be fail-safe and provide accurate and incorruptible data. These systems must be built with an integrity factor to review and crosscheck the information being received.
Automation must assist and support ATCOs in the execution of their duties, to improve performance and reduce workload, to remove non-essential tasks, to increase efficiency, to enhance not only the job satisfaction of the controller, but also the safety element of the controller’s task .”
The Human Factors aspects of Automation must be fully considered when developing Automated systems and should include the maintenance of essential manual skills and controller awareness.
The Controller must remain the key element of the ATC system and must retain the overall control function of the system. Safeguards must be established to ensure that the controller remains an active, rather than a passive, user of an automated system.
The legal aspects of a controller’s responsibilities must be clearly identified when working with automated systems.
If the controller is to remain in command, and if automation is responsible for conflict detection and resolution, it must inform the controller of what it is doing and how. We know from previous studies in aircraft, nuclear power plants, and elsewhere that complex automation tends to be opaque to its observers. Controllers must be informed, not only of the traffic situation, but also of the processes that are being invoked to modify that situation, if they are to remain controllers rather than simply machine monitors. If the controller is not to remain in command, then system architects must state most clearly who or what is to replace the controller, and how. Responsibility for an adverse outcome will be placed at some human’s door.
The key element of automation supporting the human cannot be over-emphasised. Unless the automation is proved totally fail-safe in operation and without the need for any human intervention, then restraints must be applied to the automated task. Far from running ahead of whatever the human can do to keep up with it, an automated system may run so far ahead that it proves impossible for the human to retrieve it should the system fail or be unable to provide the safety critical solutions that are needed. It is essential that any application of the “Free Flight Concept”, especially with regard to significant airspace capacity increases, ensures that the level of human ability to recover from any failure of automated systems is fully recognised and appropriate safeguards employed.
Although the “Free Flight Concept” envisions very important economic benefits for air carriers, and perhaps increased ATC system productivity (if fewer controllers were to be needed), it would require that a full ATM infrastructure remain in place to deal with exceptions, such as aircraft emergencies, failure of airborne systems, etc. However, assuming that the “Free Flight Concept” will permit higher volumes of traffic to be accommodated in a given piece of airspace than today, and assuming that air traffic controllers are still expected to be able to take over instantly in case of system-failure, it follows that the “Free Flight Concept” may require MORE controllers to be employed.
Further, much newer and more complex ATM automation would be required to deal with conflict prediction in a less orderly system involving random, unpredictable flight paths. This factor would also decrease the amount of time available to human managers, who would be expected to exercise flexibility in the resolution of conflicts. The new automation could potentially bring with it more problems than can reasonably be expected to be overcome.
Dr. Hugh Patrick Ruffell Smith, a very wise human factors expert, observed in 1949 that “Man is not as good as a black box for certain specific things; however, he is more flexible and reliable. He is easily maintained and can be manufactured by relatively unskilled labour.”
We should think carefully about this observation as we contemplate the shape of the future ATC system and consider the impact of the “Free Flight Concept”.
Finally, perhaps we should re-examine the definition of the “Free Flight Concept” that was originally put forward by the RTCA:
“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”.
If this definition is taken in context of the existing freedoms that air traffic controllers have in controlling aircraft, and acknowledging their abilities to provide direct routings whenever the traffic, airspace and procedures allow, then the concept of “Free Flight” is not a proposal.
We already have it!
The situation awareness of the controller must 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.
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, must rest with the pilot in command of that flight.
Procedures must 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”.
Clear guidelines and procedures must 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.
The question of de-skilling of ATC personnel must be considered when effectively delegating conflict alert and resolution action to automated systems.
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.
Computers have been proved good at detecting problems but are not necessarily good problem solvers.
The “Free Flight Concept” appears to put the human as a back-up to automation. This flies in the face of proven knowledge and existing IFATCA policy.
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 must 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”.
The “Free Flight Concept” appears linked with Airborne Separation Assurance System (ASAS). There is a marked change of direction to put the tools in the cockpit to undertake the ATC function, rather than provide those tools on the ground.
Ground based conflict alert systems and ASAS must be proven in all circumstances before the “Free Flight Concept” is adopted.
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.
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”.
It is recommended to Conference;
That this working paper be accepted as Information Material.
That IFATCA establish a Task Group to evaluate the “Free Flight Concept” with a view to determine an IFATCA Concept Document on the future of ATC.
NOTE: Following significant discussion at Conference, the majority of Conclusions were adopted as Provisional Policy, as shown at the beginning of this Chapter.
Aviation Automation: The Search for a Human-Centered Approach. 1997. Charles E Billings.
Controller Situation Awareness in Free Flight, Mica R Endsley, Richard H Mogford and Earl Stein, Proceedings of Human Factors and Ergonomic Society 41st Annual Meeting.
Free Flight and the Pilot, Capt. Peter M Foreman, IFALPA, SMi: Air Traffic Management 11, Prospects for Free Flight Conference, London, 1998.
RTCA: Board of Directors’ Select Committee on Free Flight (1995).
Situational Awareness in ATC – a Model, Bert Ruitenberg, IFATCA Human Factors Specialist, The Controller Magazine, Volume 36, 1st Quarter 1997.
Smith et al, “Can Automation enable a cooperative future ATM system ?”, 9th 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.
Working Paper 93/1997, IFATCA Conference, Taipei 1997 Working Paper 84/1998, IFATCA Conference, Toulouse 1998.
Working Paper 74/1991, Automation and the ATCO – Human Factors Consideration, IFATCA Conference, Port of Spain 1991.
Last Update: September 28, 2020