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Free Flight - Flight Management SystemBrite/EuRam project

3FMS

FREE FLIGHT SCENARIO DEFINITION

(3FMS - FFDD)

P/N: WP 1.1

Rev: 04c

Date: September 9, 1998

Author Review

NLR - H.HuismanNLR - N. de GelderNLR - J. HoekstraNLR - M. Mesland

SXT, AS, SI, ETG, RTSN2, DERA

ApprovalsSXT AS SI ETG NLR RTSN2 DERA

3FMS FREE FLIGHT SCENARIO DEFINITION

3FMS PROJECT 2 $WPM2AF1.doc



1. INTRODUCTION .................................................................................................................... 5

2. BACKGROUND....................................................................................................................... 5

3. EXPLORATORY AND EMPIRICAL DATA ......................................................................... 5

3.1 INTRODUCTION .................................................................................................................... 53.2 HIGH FIDELITY SIMULATION EXPERIMENTS ............................................................................ 63.3 OFF LINE SIMULATION EXPERIMENTS ..................................................................................... 73.4 PRE-OPERATIONAL STUDIES .................................................................................................. 93.5 CONCEPT DOCUMENTS AND GENERAL PAPERS ........................................................................ 93.6 CONCLUDING..................................................................................................................... 10

3.6.1 Summarising the literature review ............................................................................. 103.6.2 Responsibility............................................................................................................ 103.6.3 Conflict detection ...................................................................................................... 113.6.4 Conflict resolution..................................................................................................... 113.6.5 Communication ......................................................................................................... 123.6.6 Operational procedures............................................................................................. 123.6.7 HMI issues ................................................................................................................ 133.6.8 Conclusion ................................................................................................................ 13

4. AIR TRAFFIC MANAGEMENT .......................................................................................... 13

4.1 AIRSPACE ORGANISATION & MANAGEMENT ....................................................................... 134.2 AIR TRAFFIC FLOW MANAGEMENT ..................................................................................... 144.3 SEQUENCE MANAGEMENT & OPTIMISATION........................................................................ 154.4 SEPARATION ASSURANCE ................................................................................................... 154.5 AIRCRAFT OPERATIONS ...................................................................................................... 194.6 EXTERNAL AGENCIES OPERATIONS ..................................................................................... 194.7 EATMS TARGET OPERATIONAL CONCEPT.......................................................................... 19

5. FROM RESPONSIBILITIES TO ROLES AND AIRCRAFT CAPABILITIES.................. 20

5.1 GENERAL........................................................................................................................... 205.2 OPERATIONS IN FREE FLIGHT AIRSPACE .............................................................................. 205.3 OPERATIONS IN MANAGED AIRSPACE.................................................................................. 205.4 AIRPORT OPERATIONS........................................................................................................ 215.5 TECHNOLOGY .................................................................................................................... 22

6. FROM ROLES TO TASKS FOR OPERATIONS IN FFAS................................................. 22

6.1 GENERAL........................................................................................................................... 226.2 TRAFFIC SEPARATION CONFLICT DETECTION TASK .............................................................. 226.3 TRAFFIC SEPARATION CONFLICT RESOLUTION TASK ............................................................ 226.4 ROUTE OF PREFERENCE TASK ............................................................................................. 236.5 AIR-GROUND CO-ORDINATION BEFORE RESOLUTION EXECUTION......................................... 236.6 AIR-AIR CO-ORDINATION BEFORE RESOLUTION EXECUTION ................................................ 236.7 AIR-GROUND CO-ORDINATION FOR SEQUENCE OPTIMISATION ............................................. 246.8 AIR-GROUND COMMUNICATIONS IN NON-NORMAL SITUATIONS ............................................ 24

7. FROM ROLES TO TASKS FOR OPERATIONS IN MAS.................................................. 24

7.1 GENERAL........................................................................................................................... 247.2 MAINTAINING SEPARATION ................................................................................................ 247.3 MONITORING SEPARATION ................................................................................................. 25

8. FROM ROLES TO TASKS & PROCEDURES FOR AIRPORT OPERATIONS .............. 25

8.1 GENERAL........................................................................................................................... 258.2 CONFLICT DETECTION ........................................................................................................ 258.3 CONFLICT RESOLUTION ...................................................................................................... 25

9. 3FMS OPERATIONAL SCENARIO (IN FFAS AND MAS)................................................ 25



9.1 AIRSPACE STRUCTURE........................................................................................................ 259.2 TRAFFIC DENSITIES ............................................................................................................ 269.3 TRANSITIONING BETWEEN AIRSPACE REGIMES .................................................................... 269.4 AIRCRAFT EQUIPMENT MIX (INTEROPERABILITY IN AIRSPACE REGIMES) .............................. 279.5 AIRBORNE SEPARATION ASSURANCE................................................................................... 279.6 ROUTE OF PREFERENCE TASKS............................................................................................ 309.7 OPERATIONAL PROCEDURES................................................................................................ 309.8 MODES OF OPERATION........................................................................................................ 319.9 TYPICAL FLIGHT ................................................................................................................ 31

ABBREVIATIONS ........................................................................................................................ 35

REFERENCES............................................................................................................................... 36

APPENDIX: DEFINITION OF ADS-B REPORT ........................................................................ 50



1. IntroductionThis document is written as part of work package 1.1 of the 3FMS (Free Flight Flight ManagementSystem) under contract of the European Commission, DG XII.The purpose of this document is to describe an inventory of on going research and regulations regardingfree flight or free flight related issues. Next the results of research which is relevant for the 3FMS project isidentified. Based on this a general scenario has been identified which can serve as the initial starting pointfor the 3FMS design. This scenario will proof to be subject to changes during the project because the freeflight community itself is subject to many changes and a stable situation has not been reached yet.

The document starts with some background information in chapter 2, a literature review in chapter 3,followed by a description of the ATM environment as being concluded to be most likely out of the literaturereview. Chapter 5 translates the responsibilities from the various parties (pilots or controller etc.) in ATM toroles of these parties. Chapter 6, 7 and 8 translate these roles to more detailed tasks. Chapter 9 finallydescribes the scenario which will be used as the common starting position for the design of the 3FMS.

2. BackgroundThe current growth and the future expected growth of air traffic can not be catered by the current methodof air traffic management. Being able to serve significantly more aircraft than nowadays requires a change.Such a change might be introducing decision aiding tools and/or automating processes on the ground inorder to increase the air capacity within the current framework of air traffic management. A solution whichis currently in research is the 4D trajectory negotiation via data link between the flight crew and ATC. In thismethod traffic management is regarded as strategic (longer term) control rather than tactical (short term)control.An other solution to create an increase in air capacity is now being expected from a new kind of air trafficmanagement: free flight. Free flight is a kind of air traffic management which is set up as a distributedsystem. In other words traffic management is not performed by one central point, ATC, but by allparticipants, so all aircraft.Free flight has been defined and interpreted in several ways. It reaches from free routing, in which ATC stillhas the responsibility for separation. The other extreme is the situation in which aircraft are fully selforganised for the complete flight.High level definitions or descriptions can be found amongst others in RTCA documents and Eurocontroldocuments which both served as a basis for several research projects.This document starts as a literature review of such research projects in order to define the operationalsetting of the 3FMS project. Within 3FMS a demonstrator will be build to demonstrate the feasibility of anew technology. The experimental phase of technology development can be sub-divided as follows:• exploratory part - understanding of pressing, significant problems, identification of issues or

phenomena worth studying (algorithms, HMI, flight crew procedures, air/ground co-operation, airspacemanagement, sequencing, ATCo procedures, air/air co-operation, …) (field studies or high-fidelitysimulator studies)

• theory building part - develop causal explanations for the observed phenomena, to build theories thathave solid empirical support (laboratory studies)

• generalisation part - evaluate the generalisability of these causal explanations or set of findings undermore representative conditions (part-task simulation studies)

• hypothesis part - evaluate a theory or design intervention in a representative operational setting (high-fidelity simulator or in the field)

The 3FMS project starts with reviewing the exploratory phase as performed by others and should result inan operational simulation as part of the hypothesis phase.

3. Exploratory and Empirical Data

3.1 IntroductionIn this chapter the current status of research projects in the free flight area will be described. Because theterm ‘free flight’ is rather broad and somewhat undefined, in this chapter the main focus will be on ASAS(airborne separation assurance) which is also the main subject of the reviewed studies.The ASAS will consist of the following elements:

• - Conflict detecting algorithms;



• - Conflict resolution algorithms;• - Route of preference algorithms (upon execution of conflict resolution);• - HMI:

- conflict alerting;- display of detected conflicts;- display of resolution advisories;- display of traffic situation;- execution of resolution advisories;

• - Operational procedures;• - Possibly, air-ground co-ordination;• - Possibly, air-air co-ordination.

ASAS as regarded here does not consist of last resort collision avoidance systems like TCAS, GCAS. Thelatter are assumed to form a safetynet in order to avoid collisions and should not be evoked frequently.ASAS on the other hand focuses on separation. Separation requires aircraft movements to maintainseparation but does not require immediate action in order to avoid a threat regardless of flight economicsunlike safetynet systems which do require immediate action from the crew. The ASAS systems and thesafetynet systems have for that reason fundamentally a different and complementary function and shouldnot be mixed in any sense. Safetynet systems will not be part of this document, the technology of it will beassumed to be available for application.

This ASAS can be used to operate in a free flight ATM environment.The reviewed studies have been divided in the following categories:

• high fidelity simulation experiments• off line simulation experiments• pre-operational studies• concept documents and general papers

3.2 High fidelity simulation experimentsSeveral high- or medium fidelity simulator experiments have been conducted. This covers both flightsimulators and ATC simulators. The main conceptual differences between the experiments are the usedrules of the air or, in other words, the different conflict resolution algorithms.For each the below listed research the type of simulator is indicated, the used conflict resolution algorithmand in short the conclusion of the study.

Avans, D. and Smith, K. (1997).Simulator: B757HMI: CDTI and MCDUSeparation responsibility: air crewResolution algorithm: Pilot’s discretion based on graphical conflict alert.Conclusion: high increase of pilot workload and inefficient manoeuvres were

initiated due to the fact that other aircraft movements were difficult tointerpret.

Duong, V. N. et al (1996).Simulator: A320HMI: CDTISeparation responsibility: air crewResolution algorithm: Extended VFR rulesConclusion: Results are encouraging and can not preclude the feasibility of

autonomous aircraft operations supporting free flight.

Endsley, M.C. (1997).Simulator: ATCHMI: ATCo support toolSeparation responsibility: air crew, ATCo in case of non-nominal situationsResolution algorithm: -Conclusion: The situation awareness of ATCo’s in free flight situations can be

significantly hindered. Procedural modifications should be made tosupport the free flight concept.

Gent, R.N.H.W. van, Hoekstra, J.M., Ruigrok, R.C.J. (1997).Simulator: B747HMI: CDTI



Separation responsibility: air crewResolution algorithm: Voltage potential (modified)Conclusion: Results are encouraging and do not prove the concept to be

unfeasible even under high traffic load situations.

Hansman, R.J. et al (1997).Simulator: flight sim. and ATC sim.HMI: CDTISeparation responsibility: air crewResolution algorithm:Conclusion:

Hilburn, B.G., et al (1997).Simulator: ATC simulatorHMI: ATCo positionSeparation responsibility: air crew (notifies ATCo)Resolution algorithm: Extended flight rulesConclusion: Controller workload reduces under free flight situations. Reductions

were the largest when ATC was informed of individual aircraftmovements.

Lozito, S. et al (1997).Simulator: flight sim.HMI: CDTISeparation responsibility: air crewResolution algorithm: VFR rulesConclusion: Intention was to set up a base line experiment. Human factors

become important both on the ground and in the air. Air-aircommunication and alerting will be critical.

Mundra, A. et al (1997).Simulator: mid fidelity flight sim.HMI: CDTISeparation responsibility: partially delegated from ATC to air crewResolution algorithm: VFR for parallel runway approachesConclusion: CDTI use does not necessarily require a transfer of separation

responsibility from ATC to the air crew. CDTI in current situationalready useful in the cockpit to support current practice.

Pritchett, A.R. and Hansman, R.J. (1996).Simulator: flight sim.HMI: CDTISeparation responsibility: air crewResolution algorithm: pilot’s discretion (parallel runway approaches)Conclusion: automatic alerting required above human alerting of the operator

based on presented information only.

Scallen, S., Smith, K. and Hancock, P. (1996).Simulator: B 757 sim.HMI: displaySeparation responsibility: air crewResolution algorithm: VFR rulesConclusion: no results yet

3.3 Off line simulation experimentsMost of the off line simulation experiments focus on the conflict detection and conflict resolution algorithms.The various algorithms used can be divided in he following categories:

Alliott, J.M., Gruber, H. and Schoenauer, M. (1993).Separation responsibility: ATCResolution algorithm: genetic algorithms



Conclusion: genetic algorithms seems promising for solving complex problemssuch as a traffic situation from an ATC point of view. No referencemade to use the algorithm in the airborne system.

Brudnicki, D.J. and McFarland, A.L. (1996).Separation responsibility: ATCResolution algorithm: ground based conflict probing combined with ATCo decision aiding

toolsConclusion: ATCo decision aiding tool for planning and clearance decision making

seems promising for ATCo support.

Durand, N. et al (1994).Separation responsibility: ATC based algorithms with possible application for the air crewResolution algorithm: classical genetic algorithmsConclusion: genetic algorithms are capable or solving complex traffic situations to

be solved by ATC. No reference made to use the algorithm in theairborne system.

Eby, M.S. (1994).Separation responsibility: air crewResolution algorithm: modified potential field theoryConclusion: self organisational ATC seem very promising. Self organisational

means in this way: each individual participant acts rather than onemaster element taking the action.

Hoekstra, J.M., Gent, R.N.H.W. van and Ruigrok, R.CJ. (1998)Separation responsibility: air crewResolution algorithm: SeveralConclusion: Out of several conflict resolution algorithms the modified voltage

potential theory was found as most promising.

Krozel, J., Mueller, T. and Hunter, G. (1996).Separation responsibility: air crew until conflict is detected, then ATC takes overResolution algorithm: Euler Lagrange equations used by ATCConclusion: for conflict detection use can be made of a protected zone and an

alerting zone around each aircraft.

Paielli, R.A. and Erzberger, H. (1997).Separation responsibility: ATCResolution algorithm: pairwise resolutions (algorithm not known)Conclusion: probability of a detected conflict can be useful for conflict resolution

algorithms.

Pujet, N. and Feron, E. (1996).Separation responsibility: ATC and crew for tactical, AOC for strategicResolution algorithm: n.a.Conclusion: User preferred route optimisations defined. Taking into account

congested areas, weather, ATC constraints and tactical amendments.

Warren, A. (1997a).Separation responsibility: ATCResolution algorithm: ATC based conflict resolutionConclusion: a useful basic methodology is developed for medium term conflict

probing by ATC. The need for CNS/ATM subsystems has beenidentified.

Yang, L.C. and Kuchar, J.K. (1997).Separation responsibility: air crew if time allows this, otherwise ATCResolution algorithm: resolutions co-ordinated between crewsConclusion: conflict alerting in 4 levels has been examined, however no ATC was

assumed and returning to the initially planned route has been ignored.Alerting thresholds were defined, not satisfactory, neural networksmight become useful.

Zeghal, K. (1997).



Separation responsibility: air crewResolution algorithm: potential field force combined with sliding force theoryConclusion: potential and sliding forces form a powerful framework for airborne

conflict detection and resolution.

3.4 Pre-operational studiesVermeij, J. et al (1997a).Contribution to ASAS: specified 4D RNP values which can be adopted in a free flight

situation.

3.5 Concept documents and general papersAveneau, C. et al (1997).Separation responsibility: Temporarily delegated from ATC to air crewResolution algorithm: proceduresConclusion: based on procedures some separation tasks can be delegated to the

air crew, for example station keeping and parallel approaches.

Casaux, F. and Hasquenoph, B. (1997).Separation responsibility: Temporarily delegated from ATC to air crewResolution algorithm: proceduresConclusion: standard description method required for ASAS functions, both

technically and procedural.

EUROCONTROL (1997).Separation responsibility: air crewResolution algorithm: not described, TBDConclusion: final goal is full ASAS, migration path from now until the final goal is

required allowing mix of airspace and a mix of ASAS and non-ASASequipped traffic.

FANG (1996).Separation responsibility: delegated to air crew in defined circumstancesResolution algorithm: not applicableConclusion: Mainly ground based separation using 4D trajectories in ETMA and

user preferred routing en route. In oceanic (pair wise) off set passingsupported. Relative guidance en route and in TMA and monitoring alimited number of aircraft in the vicinity.

Krella, F. et al (1989).Separation responsibility: ground based system (human out of the loop)Resolution algorithm: not described (ground based)Conclusion: automatic managed airspace can be useful in low traffic situation, eg

at night time.

RTCA (1997).Separation responsibility: air crew eventuallyResolution algorithm: not described, TBDConclusion: a definition of free flight is given.

SAE (1997).Separation responsibility: air crewResolution algorithm: not applicable for this doc.Conclusion: full fidelity simulation experiments are required with real pilots and real

ATCo’s in order to be able to evaluate a possible free flight solution.Mental workload of pilot’s and ATCo’s should be measured, notcomputer simulated.

Sharkey, S. (1997).Separation responsibility: Temporarily delegated from ATC to air crewResolution algorithm: procedural (station keeping based)



Conclusion: simple longitudinal ASAS already feasible in mixed equipage trafficsituation, although controller and pilot workload should be considered.

3.6 Concluding

3.6.1 Summarising the literature reviewFrom the previous sections it is clear that exploratory research has been conducted on almost every areawhich is required for ASAS i.e:

• responsibility• conflict detection• conflict resolution• air-air information exchange• air-ground information exchange• operational procedures• HMI issues.

Areas which will be covered by 3FMS and which are hardly covered in the previously mentioneddocuments are:

• terrain separation, including airspace structure constraints ( in the planning and executionphase)

• weather separation (in the planning and execution phase)• free flight ground movements

3.6.2 ResponsibilityBasically three different distributions of responsibility can be distinguished between ATC and the cockpitregarding the separation with other traffic:

• ATC is responsible• cockpit is responsible• responsibility is temporarily delegated to the cockpit

All three options can be found in the literature known as free flight. The full ATC controlled version of freeflight can be regarded as a new type of ATM allowing user preferred routing, in some cases even freedomof user to select altitude and speed. But in the event of a conflict or potential conflict, ATC takes actionsand redirects one or both aircraft being in conflict. The advantages of such an environment is to createmore freedom for the airspace users without requiring major aircraft equipment adaptation. The amount ofautomation tools required to allow the ATCo to perform his task is really major. Doubtful is the airspacecapacity under such circumstances. The current ATM structure is not sufficient to allow for the expected airtraffic growth over the next coming decade(s). It is also doubtful whether it is to be expected to have world-wide the same airspace organisation. Because of the required automation for the ATCo it is evident that theATC support will heavily depend per region.

Leaving the separation responsibility fully for the cockpit will require (major) adaptation of the on boardequipment. Enabling the crew to perform the task of self separation immediately requires communicationmeans to provide the crew with information about the surrounding traffic. Presenting this traffic situation tothe crew is a naturally following requirement. Alerting the crew about conflicts and most likely aiding toolsfor conflict resolution completes the requirements.Based on the research conducted in this area it is very clear that the success of transferring the separationresponsibility from ATC to the crew depends heavily on the procedures defined in the concept.Procedures regarding the conflict resolutions are probably the most important part for a free flight conceptto become promising. Until now the following conflict resolution methods have been examined:

• VFR rules• Extended VFR rules• Cross product of speed vectors• Potential forces (modified)• Potential forces and sliding forces

The pro’s and con’s of these will be discussed in the section ‘conflict resolution’.

In case of the temporarily delegated responsibility from ATC it will be required to have a limited upgrade offlight deck functionality compared to current day practice. In this scenario ATC leaves the crew with somebasic ASAS functions as station keeping, in trail descent or climb, crossings etc. This increases the



freedom of aircraft to some extent and will increase the airspace capacity and also an increase of runwaycapacity. Increasing runway capacity is comparable to VFR approach operation in current day situations.The advantage is that it allows a mix of ASAS and non-ASAS equipped aircraft and for that reasonintroduction in the near future seems feasible. The bottom line is basically that ATC does not manage eachindividual aircraft but it manages a stream of aircraft as one entity. Still ATC manages the air traffic and thecapacity growth and freedom growth will be limited.In order to create an increase of airspace capacity and runway capacity it seems required to have ATCodecision aiding tools on the ground as well as new tools on board of aircraft. For the long term this seemsto be inefficient and less effective than the autonomous aircraft solution as described above.

3.6.3 Conflict detectionConflict detection can be roughly divided into:

• ground based• airborne• both ground based and airborne

When ground based, it is only logical to have a ground based conflict resolution as well. This means tohave ATC responsible for the separation assurance, possible temporary delegated to the cockpit.When conflict detection is airborne the conflict detection algorithm complexity highly depends on the typeof conflict resolution algorithm. Most of the airborne conflict detection algorithms described in literature arevery easy. Based on the velocity vector (with or without intent information) the minimum distance betweenthe own aircraft and the other aircraft is determined, if this distance drops below a certain minimal value, itis regarded as a potential conflict and should be taken care of by the conflict resolution function.A more complex conflict detection algorithm which could be foreseen indicates the probability of a conflictreally to occur as well. The conflict resolution function can use this probability for providing a resolution.This more complex conflict detection algorithms are mainly found in literature concerning ground basedconflict detection algorithms.Having both a conflict detection function ground based as well as airborne is foreseen to be used in ascenario in which the ground based conflict detection is a safety net for failures of the airborne conflictdetection.

3.6.4 Conflict resolutionIn case of airborne conflict detection and having the separation assurance responsibility in the cockpit, thefollowing conflict resolution methods can be found in literature:

• VFR rules• Extended VFR rules• Cross product of speed vectors• Potential forces (modified)• Potential forces and sliding forces• Genetic algorithms

The main differences found in the different simulation experiments conducted with the various resolutionmethods are found in flight safety, flight efficiency, passenger comfort, pilot workload and ATCo workload(being an arbiter, ready to take control in case of a non nominal case).

The VFR or extended VFR rules seem a logical step from standard VFR towards electronic VFR in whichavionics provides the images of surrounding traffic. However, it is found necessary to have a co-ordinationbetween the crew of the two aircraft being in conflict with each other. This co-ordination is required to letthe crew, who has priority, know that the second crew really is going to give them right of way. This co-ordination takes time and requires a long look ahead time to anticipate to a conflict. A long look ahead timemight decrease flight economy and decrease passenger comfort.

The cross product of speed vectors method uses the two speed vectors of the two aircraft and calculatesthe cross product. This cross product vector is used as the resolution manoeuvre for both aircraft. So bothaircraft will initiate a resolution manoeuvre. The magnitude of the heading, vertical speed and /or speedadjustments of the resolution manoeuvre depends on the distances from the aircraft to the predicted pointof conflict, the size of the protected zones and the current airspeeds and not on the result of the crossproduct. The advantage of this method is the co-operative manoeuvre and the transparency to the pilot.Disadvantage of this method is that it does not always yield the most cost-effective solution to a conflict.The potential forces, or voltage potential, theory is an analogy which compares traffic with electricallycharged particles. Suppose all aircraft would be regarded as negatively charged particles and thedestination would be positively charged. Summing all the repulsive forces of the traffic and the attractingforce of the destination is a way to determine a vector, which maintains separation with other aircraft and



will bring the aircraft to its destination. The potential forces has the same advantage as the cross productmethod, both aircraft are initiating a resolution manoeuvre. So even if one of the two is not acting, the otherstill is capable of solving the conflict on its own. The resolution manoeuvres are more efficient than wasfound for the cross product method. There are however situations in which a conflict is solved but bothaircraft will deviate significantly from their planned route. Enhancing the potential forces theory with the socalled sliding forces makes sure that not only the conflict is solved but both aircraft can return to theirinitially planned route in an efficient manner.

Both the cross product theory and the potential forces theory are based on easily understandableprocesses which are easy to interpret by pilots. Above that, both aircraft initiate a resolution manoeuvre.These two reasons give that it is not required to co-ordinate between aircraft which is a time savingcharacteristic of these methods which may lead to increase of safety and decrease of fuel consumption.Independent from each other the resolution can be understood and initiated.

The genetic algorithms based conflict resolution might provide an optimal solution for the aircraftconcerning safety, flight economics and passenger comfort. These methods however are based oncomplex algorithms which can not be easily understood by the human operator and for this reason maylead to loss of awareness by the flight crew. In addition it might be required to co-ordinate betweenconflicting aircraft because the unpredictability of the resulting resolution.

3.6.5 CommunicationFree flight will require communication. It depends however heavily who is responsible for the separationassurance, who is performing the conflict detection and which procedures are used and by whom initiatedto assure the separation.The possible combinations will be discussed here.-Ground based conflict detection, ground based conflict resolution, ATC responsible.

Air- ground: position report (ADS)Ground-air: resolution manoeuvre (CPDLC, R/T)Air-air: none.

-Ground based conflict detection, ground based conflict resolution, ATC delegates to cockpit, limitedairborne conflict detection.

Air-ground: position report (ADS)Ground-air: delegation authority acknowledge (CPDLC, R/T)

non nominal situation information/commands (CPDLC, R/T)Air-air: position report(ADS-B)

-Airborne conflict detection, airborne conflict resolution, cockpit responsible.Air-ground: authority transfer messagesGround-air: non nominal situation information/commands (CPDLC, R/T)

position report of non-ASAS equipped aircraft (CPDLC, R/T)constraints for entering managed airspace (CPDLC, R/T)

Air-air: position report (ADS-B)depending on algorithm: manoeuvre co-ordination info (R/T)

3.6.6 Operational proceduresProcedures are there to support the infrastructure in a way that each user of the system (i.e. the ATMsystem in this case) knows what to do in each situation and knows what to expect from the other users.

Procedures in free flight are again heavily dependent on the scenario which is used. The differences inproposed procedures are mainly introduced by the locus of responsibility. When ATC has the separationassurance responsibility, the procedures are quite similar to current day practice: ATC tells the aircraft whatto do. The situation changes when ATC delegates a part of the separation assurance responsibility to theaircraft. ATC has to indicate what is delegated to the aircraft and in relation to which other aircraft(delegated responsibility is mainly foreseen for pairwise separation) and when control is taken back. Alsoair-air procedures might be required when ATC delegated separation responsibility to a pair of aircraft tosolve a conflict or to perform a manoeuvre (for example an in trail climb/descent).

Again more possible procedures might become in use when separation assurance is the responsibility ofthe aircraft. In some scenarios the procedures are quite simple: conflict detection and resolution isperformed by both crew having a conflict with each other, both knowing what to expect from the other crewwithout direct communication between them. In other scenarios both crews have to co-ordinate in order toagree upon a certain resolution manoeuvre for one (or both) aircraft.



3.6.7 HMI issuesBoth on the ground and In the cockpit, the HMI will be required to be modified in order to support a certainfree flight scenario. The ATCo working position will not be discussed here. Cockpit HMI implication for freeflight will depend on the used free flight scenario. Depending on the locus of the separation assuranceresponsibility the cockpit requires more or less new functionality. Looking at the most demanding scenariopossible for the cockpit, ie the cockpit has the separation responsibility, there would be a need for:

• traffic information presentation• data link with ATC, display and control• alerting, for conflict detection• conflict resolution presentation• conflict resolution execution

This could be amended with weather and terrain/airspace structure presentation to be used in the flightplanning.

3.6.8 ConclusionSince the aim of free flight is to increase the airspace capacity and also more freedom for the airspaceusers to allow them to reduce operating costs assuming to maintain at least the same level of safety, thebest chances are subscribed to the free flight scenario in which the cockpit has the separation assuranceresponsibility. Airborne separation assurance guarantees a more flexible system since a distributed systemprovides fundamentally a higher flexibility than a centrally organised system.

Reviewing the potential solutions for the airborne separation assurance, the potential forces (or voltagepotential) theory with sliding forces (or similar modification) or the cross product theory, both fed by ADS-B,seems to be very promising. These two theories seem very promising regarding safety (both aircraft initiatean evasive manoeuvre), efficiency (the manoeuvre can be initiated quickly after a conflict has beenidentified without co-ordination with the counterpart aircraft. In an early stage initiating an evasivemanoeuvre will reduce the magnitude of the manoeuvre), passenger comfort (because a manoeuvre canbe initiated well in advance and the limited magnitude of the manoeuvre, passenger comfort should notsuffer), pilot workload (because the logic is easy to understand, no surprising situations have to occur),ease of understanding (closely related to the pilot workload). The ATCo workload is still an open issuebecause the role of the ATCo is nil during standard operation but might become important in case of nonnominal situations. This sudden involvement of the ATCo might be only possible when providing supporttools for the ATCo.

Summarising:

Requirements VFR rules Extended VFRrules

Cross product Voltage potential GeneticAlgorithms

Safety (requiredtime to take action,un-ambiguity ofaction)

+/- + ++ ++ +

Efficiency (flighttime and fuel burn)

- - ++ ++ ++

Comfort(magnitude ofaircraftmovements)

- - ++ ++ ++

Workload +/- +/- + + -Ease ofunderstanding

+ + ++ ++ --

(+ means advantageous for algorithms, - means, disadvantageous for algorithm)

4. Air Traffic Management

4.1 Airspace Organisation & ManagementIn the previous chapter mainly everything was discussed regarding operating in free flight airspace (FFAS).It will however be highly unlikely that aircraft will perform their flights from take off runway to landing runway



in FFAS. A more likely scenario will be that around airfields an area of managed airspace is defined inwhich ATC manages the aircraft in the proximity of runway. This means that the airspace consists of twotypes of airspace: FFAS and MAS. In addition special airspace can be foreseen, but will not be furtherdiscussed here.Aircraft flying from A to B will start in MAS, enter FFAS and close to B will enter MAS again. The result isthat the aircraft and its crew should be capable of handling three kinds of operation: operating in FFAS,operating in MAS and entering MAS coming from FFAS. The latter will require some kind of sequencing.This sequencing however has an upper limit which is dictated by the runway capacity. So entering MASwith a number of aircraft larger than the runway capacity will result in holding situations. So in addition toATC for MAS also ATFM (air traffic flow management) is required in order to make sure that the amount ofaircraft entering MAS can be handled without delay.Summarising: we need ATFM, ATC for control in MAS and ATC for arbitration in FFAS in case of non-nominal situations.

In addition to different types of airspace also different classes of users will exist. This applies certainly in thetransition from the current ATM environment towards the free flight situation. These classes of airspaceusers can be divided by their level of equipage. The main classification will be ASAS equipped aircraft andnon-ASAS equipped aircraft.Since ASAS equipped aircraft are regarded as aircraft with extended capabilities, ASAS equipped aircraftcan operate both in FFAS and MAS. Non-ASAS equipped aircraft however do not have the capability tooperate autonomously in FFAS and for this reason will need ATC support in FFAS. In order to allow non-ASAS equipped aircraft to fly from A to B two solutions can be foreseen. One solution is to have eachairport connected to other airport by at least a corridor of MAS. A second solution is to allow non-ASASequipped aircraft in FFAS which are supported by ATC for separation based on FFAS rules. Acombination of the two is also a possibility.

MAS(extensive delegated ASAS)

Country A

MAS (TMA only)

FFAS(full ASAS)

MAS entry point

Figure 1 Airspace organisation with MAS and FFAS

4.2 Air Traffic Flow ManagementAir Traffic Flow Management will have more or less the same role as in the current situation. It shouldbalance the amount of traffic from and to main airports. As explained in the introduction of the chapter,around (probably) each airport a piece of MAS will exist in order to handle the approach phase for allincoming aircraft and departure phase of all departing aircraft. ATFM should balance the traffic over the dayin a way that at each time of the day the amount of arriving and departing traffic does not exceed the MAScapacity and the runway capacity. The runway capacity is expected to be the most limiting factor.Balancing the amount of traffic in the FFAS is not regarded as required. Since all aircraft will have freedomof manoeuvring, it is expected that the FFAS capacity will not be the limiting factor of the airspace as awhole.



A possible extension of the function of ATFM is to intervene in the airspace structure itself. Airspace willconsist of FFAS and MAS. At a certain moment it might be possible to make MAS free and transfer it intoFFAS. It might also be required to transfer FFAS into MAS in certain circumstances. Transparency towardsall airspace users is of course essential in this dynamic airspace model.

4.3 Sequence Management & OptimisationSequence management and optimisation merges traffic flows from various directions (any direction intheory for free flight) and orders it into one traffic flow. This ordered and well spaced traffic flow is to beestablished to enter MAS in order to land ,mainly.This sequence management will be required on each transfer from FFAS to MAS. The location of theboundary between the two classes of airspace has to be determined yet. Possible locations are the TMAentry point, extended TMA entry point, final approach fix, etc. For the aircraft it will be preferable to havethis point as close as possible to the runway, however ATC should have the possibility to sequence thetraffic entering from the FFAS in an effective way.

This sequencing before entering MAS leads however to an ambiguous situation. Before entering the MAS,the incoming traffic stream should be sequenced already. In other words, this sequencing executed byATC happens when the aircraft are still in FFAS. It is however a more theoretical problem than a practicalproblem. The situation can be regarded as putting an extra, virtual, transition zone around the MAS inwhich ATC prepares aircraft for entering MAS while still operating in FFAS.

The sequencing process will be co-ordinated by ATC. The basic idea is that ATC provides to all incomingaircraft an RTA (required time of arrival) at the entry point. Individual aircraft may be given the responsibilityto arrive at that location at the RTA. It may also be possible for ATC to provide heading and speed vectorsto an aircraft in order to insure it arrives at the entry point at the RTA.CTAS (Center TRACON Automation System) has been indicated in free flight literature (FANG 1996, Ball1997, Krozel et al. 1996) to serve well for the sequencing problem.

4.4 Separation AssuranceSeparation assurance is the function (irrespective by whom or what it is executed) which ensures theseparation between aircraft and separation from hazards other than aircraft in FFAS, in MAS and on theground. Other hazards are terrain and weather mainly.

Separation assurance in MAS.ATC is responsible for traffic and terrain separation while operating in MAS. Weather separation will beassured by ATC only in case of severe weather.To perform this task, a communication means should be available between the ATCo and the crew.Standard R/T might be used, a more advanced solution will be CPDLC (Controller Pilot Data LinkCommunication) via ATN (Aeronautical Telecommunication Network).It is not foreseen to use full 4D trajectory exchange via data link between ATC and the aircraft whileoperating in MAS. The MAS areas should be as small as operationally feasible. Once the aircraft aresequenced by crossing specified location at a specified time with a specified speed, it should be possibleto fly through MAS towards the runway without too much extra commands from ATC. CPDLC should beable to cater for this, possibly even R/T could be sufficient.Operating in MAS does not mean that on board functionality used for operation in FFAS could not be usedin MAS. While operating MAS and sequenced by ATC, basic airborne separation functions could be usedfor procedures such as station keeping, crossing, passing, merging and parallel approaches. Stationkeeping means to follow the preceding aircraft at a certain distance with equal speed. Station keepingrelieves the ATCo from managing each single aircraft and will most likely increase the capacity by allowingsmaller separation distances (or times). Station keeping, crossing, passing and merging procedures havein common that ATC temporarily delegates executive responsibility to (or instructs) the aircraft to maintainseparation with another aircraft. ATC remains responsible for separation assurance, initiates and ends theprocedure and sets the separation standards.

Separation assurance in FFAS.In FFAS the separation assurance for traffic, terrain (including airspace structure constraints) and weatheris fully the responsibility of the crew for an ASAS equipped aircraft.For traffic separation most of the separation algorithms use the RTCA described protected zone and alertzone around each aircraft.



Protected

Zone

Alert

Zone

Figure 2 Protected and Alert Zones (RTCA definition)

Regarding the traffic separation algorithms, many possible algorithms are available as can be seen in theliterature overview in chapter 3. To give an example of an algorithm which complies with the requirementsstated the conclusion section of chapter 3, the coupled forces or voltage potential theory is described brieflyhere. This example shows how use can be made of, the so called, protected zones of aircraft. This doescertainly not mean that this is the only algorithm which complies to the requirements and which uses theprotected zones definition.The coupled forces or voltage potential is an analogy, which compares traffic with electrically chargedparticles. Suppose all aircraft would be regarded as negatively charged particles and the destination wouldbe positively charged. Summing all the repulsive forces of the traffic and the attracting force of thedestination is a way to determine a vector, which maintains separation with other aircraft and will bring theaircraft to its destination. See figure 3.

Figure 3 Simplistic view of voltage potential

This resolution method is much too simplistic to be used in free flight. For example no minimum separationis guaranteed and attraction to destination varies with distance to destination. It is also quite impractical tosum the repulsive forces of all aircraft even the ones with which no conflict currently is predicted. At theLincoln Laboratory (MIT, MA, USA) an algorithm has been developed which retains the basic repulsionfeature of the voltage potential but has a more pragmatic approach to solving conflicts (see fig. 4). Thismethod has been slightly modified for use in the resolution module.



Figure 4 Geometry of resolution method

When a predicted conflict with traffic has been detected by the conflict detection module, the resolutionmodule uses the predicted future position of the subject aircraft (called the ownship) and the traffic orobstacle aircraft (called the intruder) at the moment of minimum distance. The minimum distance vector isthe vector from the predicted position of the intruder to the predicted position of the own ship. Theseparation vector is calculated as the vector starting at the future position of the own ship and ending at theedge of the intruder's protected zone, in the direction of the minimum distance vector. The length of theseparation vector is the amount of intrusion of the own ship in the intruder's protected zone and reflects theseverity of our conflict. It is also the shortest way out of the protected zone. Therefore the own ship shouldtry to accomplish this displacement in the time left till the conflict. Dividing the separation vector by the timeleft yields a speed vector which should be summed to the current speed vector to determine the advisedspeed vector. The result is an advised track and a ground speed. Using the three-dimensional vector alsoan advised vertical speed is calculated. In case of multiple conflicts within the look-ahead time, theseparation vectors are summed.

This resolution method assumes the intruder does not manoeuvre to avoid the conflict. However in thenormal situation the intruder aircraft does manoeuvre which leads to relatively small resolution manoeuvresto be executed by both aircraft. In case the intruder aircraft does not manoeuvre, the conflict is still beingsolved however. This is part of the fail safe principle of this particular concept but could be applicable toother resolution algorithms as well providing a safety benefit worthwhile explaining here. Two differentphilosophies are possible with respect to the behaviour or the intruder aircraft, either the intruder does notperform a separation manoeuvre (in this case priority rules have to be applied to determine who has to giveway and who not) or the intruder also manoeuvres to resolve the separation conflict.In this second case using the same resolution algorithm will always result in a separation vector in theopposite direction because of the geometry of the conflict (compare the future positions with the chargedparticles). Therefore an effective co-operation is achieved without negotiation or additional communication.This also means the initially calculated advised heading and/or speed changes will normally not berequired. As soon as the conflict disappears, the current heading, speed and/or vertical speed can bemaintained. This means both aircraft 'suffer' equally due to the conflict.Both aircraft can choose whether they solve the conflict horizontally or vertically and they initially calculatethe resolution advisory as if the other aircraft does not avoid the conflict. This means a total of fourmanoeuvres is available, which all are able to solve the conflict independently. Performance limits, weather,restricted airspace will sometimes inhibit one or two manoeuvres but rarely all four. When this wouldhappen, the backup modes like TCAS could become critical. Using a look-ahead time of five minutesensures there is time enough to identify the problem and solve it.

An example of priority rules is taken from FREER. Six rules are used to determine which aircraft must makethe evasive action when an encounter occurs and when the action must be taken. To identify which aircraftmust manoeuvre or give way the priority assignment considers the aptitude to manoeuvre of each aircraftinvolved, navigation constraints associated to the trajectory of each aircraft and distance to the separationconflict of each aircraft. The first two considerations are taken into account through weights factorassociated with different phases and sub-phases of flight.The rules proposed by FREER are:1. When an encounter situation occurs between aircraft operating in normal operation, and which are in

the same phase and sub-phase of flight, the aircraft further to the crossing of the tracks must give wayto the one closer to the crossing.



2. When an encounter situation occurs between aircraft operating in normal operation, and which are indifferent phase and sub-phase of flight, priority is assigned according to the combination of phase andsub-phase of the aircraft involved.

3. The general rule to identify priority for encounter involving more than two aircraft is as follows:• aircraft which has higher manoeuvrability should give way to the one(s) which has (have) lower

manoeuvrability• if the manoeuvrability of all aircraft is equal then the aircraft which has a lower level of navigation

constraints should give way to the one(s) which has (have) a higher level of navigation constraints• if the manoeuvrability and level of navigation constraints of all aircraft are equal then the aircraft in

normal cruise has priority over the one(s) in pre-descent cruise and final climb; the aircraft in pre-descent cruise has priority over the one(s) in final climb; and the aircraft in initial descent has priorityover the one(s) in intermediate climb.

• otherwise the one that is further to the encounter should give way to those closer to the encounter.4. When a lower category of operation encounters a flight of higher priority of operation it should give way

to that flight (e.g. normal operation should give way to lifeguard/medical operations)5. The minimum distances to the acknowledgement of the encounter, priority assignment, and to the

execution of the manoeuvre are as follows:• encounter acknowledge: 70 NM to encounter• priority identified: 60 NM to encounter• manoeuvre started: 50 NM to encounter

6. Responsibility for solving encounters between different equipped aircraft (e.g. IFR, VFR, EFR, Military)is assigned according to the equipment combination of the aircraft involved.

Terrain, airspace structure constraints and weather separation will not be described here in detail, but aremark must be made that both terrain and weather separation concerns strategic separation. So noimmediate avoidance manoeuvres as result of, for example, GPWS is meant here.Terrain, airspace structure constraints, weather and traffic separation basically differ in look ahead times.Terrain has an infinite look ahead time because of its stationary character, weather and traffic are notstationary, but to some extent predictable.

Separation assurance on the ground.Currently ground traffic is monitored from the tower visually, sometimes assisted by a ground radar, andR/T communication is used by both controllers and flightcrew for position confirmation. The flightcrew isresponsible for separation assurance however. Ground radar is not widely used and has specific problemsregarding signal blocking and multipath. The flightcrew is not (yet) provided with this radar information.Airport markings, lights and signs and a paper map are used to navigate on the airport surface. Traffic andobstacles are picked up via visual scan of the outside scene. The flightcrew is therefore very dependent ofground support, especially under bad visibility conditions, and consequently the (drastic) reduction of taxispeed will be used to avoid conflicts with other traffic and ensure safety. Reductions in taxi speed alsooccur in cases when aircraft become spatially disoriented, and must engage in time-consuming interactionswith ground controllers. This decreases the capacity on the ground dramatically, especially in low visibilityoperations.

Although ground movements are part of the defined MAS in the future ATM environment, the flightcrew isfrom touch down until parking at arrival or from starting to taxi until take-off at departure responsible for theseparation assurance. ATC provides the flightcrew with the prescribed route on the ground, taking intoaccount the traffic situation on the ground, the flight plans, airspace occupancy and flightcrew requests.Although the flightcrew is responsible for separation, ATC will monitor the traffic situation on the groundand provide the flightcrew with directives to prevent conflicts and to smoothen the taxi phase. For exampleaircraft may be directed to stop at a certain position and wait until another aircraft has passed or to increaseor reduce speed to smoothly prevent a conflict from happening without having to stop. Under bad visibilityconditions ATC will increase separation distances, which also contributes to a reduction of airport capacity.

Enhancement of the flightcrews situational awareness concerning traffic may enable a reduction ofseparation distances and a higher taxi speed under bad visibility conditions while maintaining safety. Heretotraffic information (other a/c and ground vehicles) and an airport map could be presented to the flightcrew.To present the flightcrew with traffic information use can be made of the broadcasted data of ADS-Bequipped vehicles.Ground-to-ground ADS-B for airport surface surveillance, making use of DGPS, is currently feasible andprovides accurate position and identification of aircraft and other equipped vehicles. This wasdemonstrated by FAA trials using ground-to-ground ADS-B at Boston's Logan International Airport in early1994 which indicated excellent ground surveillance coverage (one hundred percent coverage wasachieved with 1 second update rates out to 10 nm from the ground stations).



Future surveillance may be exclusively based on ADS-B, but currently the air traffic system is occupied withnon ADS-B equipped vehicles. Ground radar systems may be used to let ATC provide (by datalink) theinformation regarding non-ADS-B equipped vehicles. Hereto new systems are under development, like theFAA ATIDS (Airport Surface Target Identification System), that combine identification data with groundradar technology to provide reliable tracking information. However transponder (Mode A/C or S) equipagewill still be necessary.

Non-transponder equipped aircraft and vehicles are not able to be "seen" by others and the number ofairports equipped with advanced surveillance systems is still limited. Therefore improvement of bad visibilityoperations is only feasible in distinct situations and is very dependent on the equipage level of the presenttraffic mix.

In the near future it is foreseen that when a number of ASAS equipped aircraft sequentially operate on theground, use can be made of station keeping techniques. The required traffic information, the statusinformation of the taxi route (e.g. stop bar lighting) could then be presented in the cockpit e.g. throughdatalink. The benefits of the use of this kind of operation are that they are possible under bad weatherconditions, R/T communication (and the resulting misunderstandings and congestion) is reduced, theflightcrews situational awareness is increased, which leads to better predictable taxi times and possibly toshorter taxi times, which in turn allow for a reduction of delays due to ground operations and an increase ofairport capacity.

4.5 Aircraft OperationsThe aircraft operations described in the previous sections mainly concern separation with respect to traffic,terrain and weather in the various classes of airspace. These issues all concern the safety to the flight. Inaddition to safety, efficiency is important. In current day practice a route is planned from A to B via a SID,structured airway routes and a STAR. Using an FMS, the FMS calculates the most efficient way to reach Bgiven all the constraints implied by ATC and given all the setting implied by the company. In a free flightsituation the SID and STAR will still exist as part of the MAS. Between the SID and STAR the flight willmainly (totally) be performed in FFAS. The FMS should be able to plan the most efficient route between theend of the SID and the start of the STAR taking into account company policy, weather constraints andterrain separation. The resulting route is the route of preference. This all still concerns the planning phaseof the flight.During the flight it will be unlikely that this route of preference can be flown without any deviation due totraffic or weather. After being deviated from the route of preference due to traffic (unexpected weather, etc)the aircraft should or return to this route of preference, or a new route of preference should be defined fromthe present position of the aircraft. Returning to the route of preference (updated or not) ensures theaircraft to arrive indeed at B, having departed from A. This route of preference is basically not part of thefree flight scenario, but is still a requirement to make sure that free flight is operationally acceptable.

4.6 External Agencies OperationsAgencies required for safe and efficient operations in FFAS, not yet covered until now, are for instanceAOC and ATS services. AOC will interact with the aircraft at least in a similar way as nowadays usingACARS but most likely more intensively. AOC will take care of strategic planning for the aircraft based oncompany related decisions like RTA modification due to gate assignments, connecting flights etc. Theseissues will not be discussed here in more detail.ATS services other than ATFM and ATC will be automatic services, FIS (Flight Information Services). Thismight be non free flight related services, like ATIS uplink and meteo services. A free flight related servicewhich becomes important in traffic mix situations will be the position report uplink of non-ADS-B equippedaircraft by ATS in order to allow the self separating aircraft to have position knowledge of all aircraft, notonly the ADS-B equipped aircraft.

4.7 EATMS Target Operational ConceptHow does all the previous compare to the European vision of future ATM? For this we refer to theOperational Concept Document (OCD) from EATCHIP (EUROCONTROL) as a proposed target conceptfor EATMS (European Air Traffic Management System), EUROCONTROL and European Commission.This target concept description includes a transition scheme from 2000 to 2015 and beyond. It foreseesintroduction of free routing in European upper airspace in 2003 and airborne separation starts in 2009.Free flight in its full extend is foreseen to be introduced between 2010 and 2015.The OCD defines MAS, FFAS and UAS (Unmanaged Airspace):

MAS: Managed airspace is airspace where the responsibility for aircraft separation is primarilyground based.



FFAS: Free flight airspace is airspace where the use of free flight mode (FFM= operationsmode comprises both free routing and autonomous separation) is the normal mode ofoperation.

UAS: Unmanaged airspace is, in essence, subject to the rules currently applied outside ofcontrolled airspace.

The OCD further states that SIDs and STARs will continue to exist and that probably during peak traffichours, large parts should be MAS to ensure sufficient capacity.

Entering FFAS is only permitted for well equipped aircraft, or in case of non-ASAS equipped aircraft,explicit permission from ATC is required because non-ASAS equipped aircraft need ATC support.

The aim will be to adjust the FFAS size in a way that the ASAS equipped aircraft gain the highest benefitsoperating in the future EATMS.

In what way aircraft have to be autonomous however has not yet been defined and is still an open issue.

5. From Responsibilities to Roles and Aircraft Capabilities

5.1 GeneralBased on the airspace organisation in MAS and FFAS with each their own distribution of responsibilities,the roles of the various users and the required aircraft capabilities can be determined.

5.2 Operations in Free Flight AirspaceRole of the flight crew.The flight crew is responsible for the traffic, weather and terrain, including airspace structure constraints,separation. Traffic separation means to detect conflicts (most likely to be alerted by cockpit automation)and to execute a resolution manoeuvre complying with the rules of the air (possibly/probably proposed bycockpit automation). Concerning weather and terrain (including airspace structure) separation, the crew isrequired to check the planned route (also after a resolution manoeuvre has been initiated)against theweather and terrain hazards (possibly/probably supported by cockpit automation).Apart from this role the crew has to obey ATC constraints before entering MAS coming from FFAS.

Role of the ATCo.The ATCo performs the role of an arbiter. In the nominal situation with 100% equipped aircraft the ATCohas no active function other than monitoring. In case an aircraft does not obey the rules, in case of anaircraft equipment failure or in an emergency, ATC will intervene in order to ensure no loss of separation.An other role of ATC is to support non-ASAS equipped aircraft while crossing FFAS. Non-ASAS equippedaircraft should only enter FFAS by exception and after explicit permission of ATC. This is probably onlypossible in low traffic situations, i.e. ATCo workload permitting situations. ATC will perform the conflictdetection and resolution for the non-ASAS equipped aircraft in such a way that ASAS equipped aircraft inthe surrounding experience this non-ASAS aircraft like any other aircraft.Furthermore the role of the ATCo for traffic in the FFAS is to prepare them for entering MAS again. Thismeans to guide an individual into its place in the sequence of aircraft entering the MAS.

Aircraft capabilities.To support the crew in order to be able to assure separation to other traffic, weather and terrain thefollowing system or capabilities should be available to the crew:

• ASAS: conflict detection, conflict resolution, HMI• 3D RNAV• RNP X• ADS-B• Air-ground data link• RTA (ETA probably not sufficient)• data base (terrain, weather, airspace structure etc.)

5.3 Operations in Managed AirspaceRole of the flight crew.



In MAS the separation is assured by ATC, with possibly temporarily delegation to the crew. This means thatthe role of the crew is to execute directives from ATC like in the current ATM structure. These directivescan be provided by R/T or by data link (CPDLC). In case the ATCo decides to delegate traffic separationresponsibility to the crew, the crew will be asked to perform some kind of spacing. This can be for instancefollowing the aircraft in front of them at a certain distance or to monitor/perform a parallel runway approach.

Role of the ATCo.In MAS the ATCo has the responsibility for the separation. This means that the ATCo will provide directivesto the crew via R/T or data link. Spacing techniques like station keeping can be used by the ATCo in orderto manage one set of aircraft as one entity rather than a set of aircraft as individual entities. This might leadto smaller separation distances and thus to an increase in airspace capacity.

Aircraft capabilities.Aircraft operating in MAS can be either ASAS equipped aircraft or non-ASAS equipped aircraft. Theamount of required aircraft capabilities is for this reason not too high. When operational ASAS proceduressuch as station keeping, passing, crossing and merging are required this changes.

Operating in MAS without ASAS procedures requires:• 3D RNAV, RNP X, R/T in other words, the current day practice requirements• Air-ground data link (optional)

Operating in MAS with ASAS procedures requires:• 3D RNAV, RNP X• ADS-B• TIS-B: Air-ground data link for position report uplink of non ADS-B aircraft• Air-ground data link for CPDLC (optional)• ASAS: separation manoeuvre techniques, HMI

5.4 Airport OperationsRole of the flight crew.On the airport surface the separation assurance is the flightcrews responsibility. However ATC provides theflightcrew with the route to be followed and directives that have to be executed. The flightcrew has to detectconflicts and execute resolutions (supported by cockpit (alerting) automation). On ground resolutions willbe limited to speed changes since the taxi route is pre-determined.

Role of the ATCo.During on ground operations, ATC is responsible for the provision of routings from gate to runway and viceversa that can be met by the aircraft. ATC will hereto take into account the on ground traffic situation ofarriving and departing aircraft, the flightplans of the individual aircraft (e.g. planned time of departure,planned route to take into account airspace congestion along the route) and aircraft requests (e.g. whenan aircraft declares itself ready for engine start, push-back, or taxi start, permission may be granted eventhough another aircraft that has not yet declared itself ready may have an earlier planned take-off time).ATC will monitor the on ground traffic and provides directives.Dependant on the traffic mix, the ATCo may use station keeping techniques to manage a set of ASASaircraft as one entity when they are sequenced properly and conflicts with non-equipped aircraft or vehiclesare not foreseen. In this case ATC has to keep the ASAS flightcrews updated on the positions of relevantnon-equipped aircraft or vehicles and ATC has to provide proper directives to the non-equipped vehicles.

Aircraft capabilities.The aircraft operating on the airport surface can be either equipped with ADS-B or Mode A/C or Stransponders or not. The surveillance capabilities at the airport determines the level of equipage necessaryto be "seen" by others. Therefore only at specific operational circumstances (weather, traffic mix)improvement of taxi operations is foreseen. In order to improve bad weather operations (reducingseparation and increasing taxi speed) the aircraft should have the following capabilities:• ASAS conflict detection, conflict resolution, HMI• RNP X, required on ground navigational accuracy• ADS-B• Station Keeping functionality (optional)• Air-ground datalink for position uplink of non ADS-B aircraft• Air-ground datalink for CPDLC (optional)



5.5 TechnologyIn the previous sections requirements are stated regarding required equipment on board forcommunication, navigation and surveillance (CNS) for operation in free flight with ASAS. How do theserequirements relate to the current state of CNS technology as reflected in FANS A and FANS 1 and howdo they relate to future developments in CNS as reflected in FANS B and FANS 2?With respect to Communication, data link is foreseen for communication to AOC, ATC and other aircraft.Current developments in the area of FANS B foresee the use of ATN between the aircraft, ATC and AOC.So the only one which is not yet covered is the aircraft to aircraft data link. Whether aircraft to aircraftcommunication requires data link or whether R/T is sufficient can not be identified here yet. With respect tocommunication between the crew and the ATCo, a subset of the CPDLC message set DO 219 couldserve as a basis, however extensions are foreseen.With respect to Navigation, FANS A/1 supports navigation accuracy expressed in an RNP value (see DO236). FANS B/2 will continue in this area. The exact value of the required RNP is to be defined yet, but forthe moment the FANS developments are in line.With respect to Surveillance, ADS is required as well as ADS-B. ADS is part of FANS A/1 (see DO 212).ADS-B however is not covered in FANS A/1 but might be introduced in FANS B/2 although the decisionhas not been taken yet.Conclusion is that the requirements regarding available technology for free flight with ASAS are to a verylarge extend already covered in FANS developments. Specific items, like communication specific related toconflict resolution methods, conflict detection methods, transfer of authority, taxi procedures, crew-crew co-ordination procedures and FIS is obviously not covered. These specific items however require most likelyno extra technology, just specific use of the existing or planned technology.

6. From Roles to Tasks for Operations in FFAS

6.1 GeneralIn the previous chapter the role of the flight crew and ATC has been identified. Now stepping one leveldeeper into detail, the tasks for the crew and ATCo can be determined. Based on these tasks it should bepossible to define functions for both man (the crew) and machine (cockpit automation tools) which make itpossible to perform the identified tasks. This chapter focuses on the tasks in FFAS.

6.2 Traffic Separation Conflict Detection taskIn FFAS, the role of the flight crew is amongst others to assure traffic separation. Detection of a conflictwith other traffic is the basis for this. The conflict detection task will consist of finding the minimum closuredistance between the own aircraft and all other traffic with the surrounding. It is immediately clear that ‘thesurrounding’ needs to be defined in order to be sure that those aircraft are surveyed which are of interest.Next a threshold should be defined for the minimum closure distance which defines whether a certainclosure distance is called a conflict or whether it’s not.More complex conflict detection algorithms can be used. For example determining the probability of aconflict to really becomes a threat to the own aircraft. It is however not foreseen to use this kind ofadvanced conflict detection algorithms because the advantages do not seem to pay off to thedisadvantages.

The conflict detection task will be allocated to the automated system rather than to the flight crew. A systemdetected conflict will be presented, and alerted, to the crew on the HMI.

6.3 Traffic Separation Conflict Resolution taskAfter having detected a conflict the conflict resolution task acts on it, using the protected zones of theaircraft involved and the conflict resolution algorithm.

The conflict resolution task might be allocated fully to the crew, assuming the resolution algorithms to beeasily applied by a human operator. More likely, this task is to be allocated to a cockpit system. For theexecution of the resolution manoeuvre again a choice has to be made for the allocation between the crewor the system. Making such a design choice, it should be guaranteed that this allocation does not decreasethe safety nor should it result in a loss of crew awareness by over-automating it. In other words theresolution should be easy to comprehend and should fit in the pilot’s mental model. In a well designedsolution, a pilot should be able to predict what the system will propose, rather than that a pilot is surprisedof how the system intends to solve a conflict.



6.4 Route of Preference TaskThe route of preference task should be performed in order to make sure that the destination will bereached in an efficient manner, allowing for the required resolution manoeuvres for traffic separation. Inaddition terrain, airspace structure and weather separation constraints should be included.The choice for allocation between the crew and the system requires again a careful decision. The systemwill be involved in order to be able to calculate a route of preference using detailed information which isimpossible for a human being to handle. On the other hand the crew should be kept in the loop to reducethe risk of loss of awareness.A change in the route of preference, possibly due to a conflict, should not result in a (new) conflict.

6.5 Air-Ground Co-ordination before Resolution ExecutionA major issue in free flight is to keep ATC involved in the traffic situation. Expecting ATC to take care ofnon-ASAS equipped aircraft, only in by exception though, to take care of aircraft with degraded ASASsystems due to system failures and also to act as arbiter in the field will require ATC to be really involved.For this arbiter function, ATC should be kept informed about airborne detected conflicts to allow the ATCoto detect whether an aircraft is taking action or not.Air-ground co-ordination can be explicit or implicit. Explicit would require the crew to contact ATC andreport what the intended resolution manoeuvre will be in case of a conflict. Experiments with ATCo’s hasfound that keeping ATC informed about what the aircraft are going to do decreases ATCo’s workload andkeeps the situation more clear. The price to be paid however is a decrease of flexibility. Flexibility meansthat an airspace user can change his direction (in one or more of the four dimensions) in any way at anymoment without co-ordination with any one. The opposite is inflexibility, meaning that an airspace user hasto co-ordinate a preferred change in direction with one or more of the other airspace parties (pilots,ATCo’s, etc.) and wait for an approval from one or more of the airspace users before actually initiating itsmanoeuvre. The first is optimal for the airspace user with the desire to change its direction while the secondis optimal for the airspace users other than the one desiring to change its direction. In other words, withdefining co-ordination before manoeuvring, the flexibility of the system is defined as well.The practical implication of requiring co-ordination and reducing the flexibility in some way will lead to alonger time between conflict detection and conflict resolution. This time can be created in two ways. First tolook more in advance, so trying to detect a conflict as early as possible with a possible consequence ofmore false alarms. The second possibility to create this time is manoeuvre later. Initiating the evasivemanoeuvre later means that a larger rate of manoeuvre (i.e. rate of turn or rate of climb/descent) will berequired which has a negative effect on passenger comfort and flight economics. Concluded can be thatflexibility is advantageous and should be kept high.

Implicit co-ordination might be automatic downlinking the intended manoeuvre without crew interaction.This would not affect the flexibility, but the question is whether is would be sufficient for the ATCo.

Since the air-ground co-ordination depends probably highly on the rules of the air and not much researchhas been performed in this area it is difficult to say at forehand whether air ground co-ordination is requiredand how it should be implemented.

6.6 Air-Air Co-ordination before Resolution ExecutionAir-air co-ordination is required mainly when in a conflict situation it is not evident to the crew what the crewof the conflicting aircraft is supposed to do or can do. If on the other hand it is predictable what theconflicting aircraft will do, then air-air co-ordination is superfluous and undesirable because it takes moretime to resolve a conflict.For example, looking at the voltage potential theory or the cross product theory, these are in essence notcomplicated and resolutions are easily understood by the human operator. In addition, the initial resolutionmanoeuvre is based on the assumption that the conflicting aircraft does not take any action. These twocharacteristics of these algorithms lead to the assumption that no air-air co-ordination is required. Using aresolution method which does not require air-air co-ordination has large advantages regarding the time tosolve a conflict and has for that reason a safety advantage.However it is found in experiments that having knowledge of the destination and the target flight level of theconflicting aircraft might become useful to choose for the most efficient resolution rather than anyresolution.

An other application of air-air co-ordination is to avoid ‘false alarms’. This is more part of the conflictdetection rather than conflict resolution.



6.7 Air-Ground Co-ordination for Sequence OptimisationAir-ground co-ordination for sequencing will be required. This is basically a kind of traffic co-ordination byATC by giving constraints to aircraft in FFAS. Sequencing is assumed to be the process of sequencing astream of aircraft, each individual aircraft will have to cross a certain point with a certain altitude at a certaintime with a certain speed. The ground will have to define the position, the altitude, the time and the speedto enable this. ATC will have to provide the required altitude, required time and required speed at the fix.For aircraft not having ASAS capabilities, ATC will have to vector them to the fix in order to create abalanced incoming traffic stream.This air-ground co-ordination might be performed by using data link (CPDLC) or standard R/T.

6.8 Air-Ground Communications in non-normal situationsAlthough data link will be very likely to be available it is not foreseen to use data link in abnormal oremergency situations for the aircraft having the non-normal situation. Such a non-normal situation requiresa fast response time from the ATCo and a clear feedback of the ATCo. R/T provides fast response timefrom the ATCo and gives immediate feedback in what way ATC can assist in the non-normal situation. Inaddition, R/T provides the advantage of the so called party line effect which allows aircraft In thesurrounding to be informed directly.Data link however might become useful to notify other traffic in the surrounding that a specific aircraft is in anon-normal situation and that this particular aircraft has priority to all traffic and will not initiate a separationmanoeuvre in order to reach the closest airport as soon as possible. The crew of the aircraft with the non-normal situation can now concentrate fully on the situation they are in.

7. From Roles to Tasks for Operations in MAS

7.1 GeneralOperating in MAS will be very similar to current day operations with ATC in control providing clearances toall aircraft. This kind of operation will require no more than standard equipment. However ASAS equippedaircraft can make beneficial use of its ASAS functionality, even in MAS.In MAS, ATC has the separation responsibility, so conflict detection and resolution functionality is notrequired nor useful. It is however possible to delegate responsibility from ATC to the flight crew to maintainseparation to one or two other aircraft. This separation was already accomplished by ATC control.Maintaining already established separation be used in new ASAS procedures such as station keeping,crossing, passing, merging and parallel approaches. Two classes of procedures can be identified: a) theflight crew only monitors (e.g. parallel approaches) and b) the flight crew actively controls to maintainseparation. Only these two will be further discussed here.

7.2 Maintaining SeparationAfter entering MAS and being fully under ATC control again, ATC can partially delegate separationresponsibility to the crew: station keeping, passing, crossing, merging. While station keeping, the crewfollows exactly the same lateral route as the preceding aircraft. It is tasked (by ATC) to follow this aircraft ata distance of X NM at the same altitude, or possibly at a slightly different altitude.The aircraft which has to be followed is preferably an ASAS equipped aircraft which ensures the bestposition (and intent possibly) information. But this is not a requirement. If a TIS-B service exists whichuplinks position information of non ASAS equipped aircraft via data link to ASAS equipped aircraft, theneven non ASAS equipped aircraft can be followed using station keeping.While passing, crossing or merging, the crew is instructed by ATC to perform a separation manoeuvre inrelation to one or perhaps two other aircraft. It is tasked to pass left or right, cross ahead or behind, mergeafter or before and simultaneously to respect the separation distance (set by ATC) to the aircraft involved.Station keeping, passing and so forth are basically digitised versions of what currently is used in VMC: theATCo asks the crew to keep visual separation to a preceding aircraft during the arrival. This increases therunway capacity and reduces controller workload. For this reason these ASAS procedures are expected tobe beneficial.



7.3 Monitoring SeparationMonitoring parallel runway approaches is comparable to station keeping. Also in this case the ATCodelegate partial responsibility to the flight crew. The crew is tasked to monitor traffic which is approachingthe other runway (i.e. the runway parallel to the one which is being approached by the ownship. Thismonitoring is mainly meant to react early when traffic for the other runway is deviating from their approachpath and forming a threat to the ownship. Leaving this monitoring to ATC will require larger separationminima because the reaction times will be larger.Parallel runway approach monitoring will, like the above-mentioned ASAS procedures, be a likely candidateto increase airport capacity.

8. From Roles to Tasks & Procedures for Airport Operations

8.1 GeneralIt has already been identified that airport operations are part of MAS operations. This, together with the factthat the freedom of movement on the ground are far less than in the air, ATC involvement will be required.The freedom of movement on the ground has basically 2 degrees of freedom (direction of taxi lane andtime) while in the air 4 degrees of freedom (3D position and time) exist.The practical implication of this is that ATC defines the required taxi route to follow. The crew is thentasked to follow this route. Until so far nothing has changed compared to the current situation.Airport operations for ASAS equipped aircraft can be enhanced by presenting the taxi route on a displaytogether with other traffic on the airport surface, aircraft and other vehicles.

The main benefit is expected to be gained in operations on complex airport by increasing the crew’ssituation awareness. A second benefit is expected from low visibility operations.

8.2 Conflict detectionConflict detection during taxiing can be performed either by the crew itself using a display (most likely) onwhich surrounding traffic is displayed or by an automated system. Automatic conflict detection is notregarded as mandatory because presenting traffic on a display and leaving the conflict detection to thecrew is very similar to current days practice. The only real difference is that the crew uses a display ratherthan outside vision to detect a conflict.Constraint for being able to perform this is however is that position reports are received from all traffic in thesurrounding. Since both ASAS equipped and non-ASAS equipped aircraft are in operation on an airportthe position reports from non ASAS equipped aircraft has to be provided by TIS.

8.3 Conflict ResolutionFor conflict resolution the same applies as for conflict detection. The crew is capable of finding a solution tothe traffic conflict very similar to current days practice. The problem is easy to comprehend and also asolution to the problem is similar to current days practice.Station keeping functionality in the sense of following a preceding aircraft like it has been described forMAS operation will be beneficial. The merging and perhaps crossing functions might bring additionalbenefits.

9. 3FMS Operational Scenario (in FFAS and MAS)

9.1 Airspace StructureWithin 3FMS the airspace will consist of three types of airspace: Free Flight airspace FFAS, Managedairspace MAS and Special airspace which can not be used. Only the first two, FFAS and MAS, will beconsidered here. MAS will exist at least around each airport. A first estimate will be to use the TMAboundaries. MAS corridors will connect MAS areas around airports allowing non ASAS equipped aircraft tofly from airport to airport without the need to cross FFAS. The existence and the size of the MAS corridors



between airports will vary through time with one main driving factor: the amount of ASAS equipped aircraft.The basic idea is to keep the ASAS and non ASAS traffic separated by airspace type. This means thatwhen the majority of the traffic consists of non ASAS aircraft the amount of MAS will be relatively large.However, ASAS equipped should be able to operate in beneficial circumstances compared to non ASASequipped aircraft.In MAS the use of structured airways is foreseen. Especially in the TMA MAS, the use of standarddeparture and arrival routes is foreseen mainly for environmental reasons. In low traffic density situationsand in case ATC has the availability of ATCo supporting tools, free routing is supported in MAS.In FFAS free routing and free flight are implemented by means of full delegation of the separationresponsibility to the flight crew by means of ASAS.

Summarising the airspace structure:In MAS, ATC is responsible for the separation assurance, in FFAS the flight crew is responsible for theseparation assurance.

9.2 Traffic DensitiesATFM (Air Traffic Flow Management) is assumed to be available and operational. This means that theamount of traffic is spread out in the planning and a peak at a certain time of the day can be limited, mainlywith respect to airport capacity.Changing from the current ATM system towards the free flight ATM system has two major driving factors:to reduce operating costs and to increase the airspace capacity allowing for a traffic growth. Within 3FMS,the peak traffic situation above Europe will be the experimental baseline situation although the 3FMS will bedeveloped for world wide application. Next the double or tripled amount of traffic will be used in order toevaluate the feasibility of the concept. In addition a traffic situation of merging or crossing traffic streams willbe used. This applies for operation in FFAS only. For operating in MAS, the amount of traffic will allow for asmaller increase than doubling or tripling the highest peak currently experienced.

Although as explained earlier it is intended traffic to be divided in airspace based on their equipment level:ASAS or non ASAS, within FFAS non ASAS aircraft are only allowed by exception. These non ASASequipped aircraft rely on ATCo support for separation from other traffic. This means that for these nonASAS equipped aircraft the ATCo performs the conflict detection and resolution role of the pilot as in theASAS aircraft.

9.3 Transitioning between Airspace RegimesSince airspace is divided in FFAS and MAS and each airport is surrounded by MAS, it is obvious thataircraft will transit from the one to the other. From MAS to FFAS during the climb out after take off will notcause any problem and will not be covered here for that reason. Vice versa, entering MAS coming fromFFAS does cause a problem. In MAS an ATCo is responsible for the separation but to be able to do thisthe ATCo shall also need to control the position and the time of aircraft entering ‘his’ airspace. As alreadyindicated before, it is assumed that fixed arrival routes will be used in the TMA MAS. This determines theposition at which the ATCo can expect aircraft to enter the MAS at a defined position, leaving the timeopen. This simplifies the problem already and brings it back to a sequencing problem. Aircraft wanting toenter the MAS should be sequenced in a way they can all follow the same arrival route from the MAS entrypoint towards the runway with sufficient separation. An example of a system which has been designed tosequence aircraft coming from different directions for an approach to the same runway is CTAS (CenterTRACON Automation System). CTAS assumes aircraft to cross a pre defined fix and detects possibleconflicts between aircraft wanting to cross the fix. Subsequently ATC will solve the problem by assigningtime constraints to individual aircraft which will result in a well sequenced queue of aircraft when actuallycrossing the fix. Although CTAS is a development to be used in the current ATM environment, it has greatpotential to be used for the FFAS-MAS transition.

CTAS will be described here in some more detail to provide an example of how the sequencing problembetween FFAS and MAS might be solved. Other solutions can be foreseen as well however.CTAS consists of a set of tools. The one tool of CTAS which is of main interest to solve the problem oftransition between FFAS and MAS is the TMA tool (Traffic Manager Advisor). The TMA tool sequencesand schedules aircraft over a certain fix (metering fix, approach fix, runway threshold, etc…). In this casethe entry point of MAS. First the sequencing process of the TMA tool is active and will construct asequenced list of arriving aircraft. Aircraft are sequenced in this list in first come first served order based ontheir ETA (Expected Time of Arrival) on the fix and based on the aircraft class. A second, more advanced,sequencing method supported by the TMA tool uses not only the ETA but also an earliest feasible ETA(also indicated as minimum time to landing). After the sequence has been established, the schedulingprocess of the TMA tool will start. This scheduling process will maintain the sequence but will assign anSTA (Scheduled Time of Arrival) to each individual aircraft in order to maintain the separation minima within



the sequence of aircraft by the time they cross the fix. An assigned STA for an aircraft will never be earlierthan the ETA (either normal or earliest ETA) of the aircraft, it will always be later. The time between twoaircraft in the sequence depends on the class of both aircraft.The TMA tool will be used normally when the aircraft are between 150 and 200 NM from the runway.

Within CTAS, a second tool, the Descent Advisor (DA) is used to advise the controller to generateclearances for individual aircraft to assure that they meet the STA at the fix and that separation ismaintained while flying to the fix. In the free flight situation however, the aircraft are still in FFAS and forthat reason the aircraft are responsible for the separation while assuring to meet the fix at the STA usingtheir 4D capabilities. For this reason the DA is not required to solve the sequencing problem within a freeflight situation.

After crossing the MAS entry point, ATC has full responsibility and a full mix of ASAS equipped and non-ASAS equipped aircraft exists. Control will proceed as described in chapter 7: MAS operations.

CTAS describes the use data link for communicating between the controller and the pilot. The toolscontained by CTAS provide clearances which can be directly used by the controller. Since only the TMAtool of CTAS is foreseen to be useful for free flight and since the TMA tool basically only defines an STA foreach aircraft out of the ETA’s of the arriving aircraft, data link (CPDLC, possibly extended with change ofauthority between FFAS and MAS messages) can be used but is not required as such.

9.4 Aircraft Equipment Mix (Interoperability in Airspace Regimes)As described earlier a number of non ASAS equipped aircraft might operate in FFAS, this however shouldbe seen as exceptions to the rule. At least the traffic density and ATC equipage must allow for it. Thissituation leads for the ASAS equipped aircraft to two problems: non ASAS aircraft are assumed to be nonADS-B equipped as well, so the position reporting of those aircraft has to be solved via a ground based TISservice. This TIS will uplink information about non-ASAS aircraft via data link to ASAS equipped aircraft,typically 3D position and 3D velocity vector, in order to allow ASAS equipped aircraft to perform theirconflict detection. As a consequence the quality of the information provided by the ground-based TIS hasto be adequate (for example, only information gathered through SSR mode A/C or SSR mode S mighthave the required quality). If the ground is unable to determine the position and velocity vector of non-ASAS equipped aircraft or can not determine it with the required quality then those aircraft are not allowedto operate in FFAS. The second problem will be the fact that these non ASAS equipped aircraft will behavein a different way than ASAS equipped aircraft. ATC will control the non ASAS equipped aircraft in order toensure separation. This means probably mainly that the reaction times of these aircraft are significantlylarger than the ASAS equipped aircraft. There are ways to simplify this problem by introducing procedures.For example, non ASAS equipped aircraft following a predefined airway will have priority over ASASequipped aircraft. In other words the ATCo has no task to separate the non equipped aircraft as long asthey are cleared for this airway. The ASAS equipped aircraft will assure separation with aircraft ‘in’ theairway. If the ATCo on the other hand cleares a non equipped aircraft outside this airway, the ATCo isobliged to support this aircraft such that it behaves like as if it was ASAS equipped from the point of view ofthe surrounding ASAS equipped aircraft. The latter situation is only feasible in low density traffic situations.

Operating in a mix of ASAS and non ASAS equipped aircraft in MAS will provide less problems than in theFFAS. The problem of non ADS-B equipped aircraft being invisible without having a TIS service stillremains, but since ATC is in control the separation problem as in the FFAS does not exist.ASAS equipped aircraft can be partially delegated with the responsibility of maintaining the alreadyestablished separation. Basically ASAS equipped aircraft should be able to follow a preceding aircraft. Thispreceding aircraft can be an ASAS equipped aircraft of which all information is directly available via ADS-B.Following a non ASAS equipped aircraft will mean that following the preceding aircraft will have to bebased on information uplinked by TIS.

9.5 Airborne Separation AssuranceAirborne separation will consist of three separation functions: traffic separation, weather separation andterrain/airspace separation. For all three, the term separation is used to indicate that no avoidance ismeant. Avoidance of traffic and terrain is regarded as being taken care by other aircraft systems forming asafetynet in case of non-nominal situations. In nominal situations, separation functions are used. Thesafetynet functions for avoidance will not be covered here but assumed to be available in the aircraft.The separation functions are all three, traffic, weather and geographic, divided in two parts: first the conflictdetection part will be activated and secondly the conflict resolution function will act upon the detectedconflicts. The resolutions for traffic, weather and geographical separation will be combined with the route ofpreference in order to define the ‘new’ trajectory.



Although the detection algorithms might differ for traffic, weather, airspace and terrain, the resolutionalgorithm will be the same for the three. Chapter 4.4 already describes a possible resolution algorithm, themodified voltage potential theory, for traffic resolution. The basic idea behind it is that all aircraft areregarded as repulsive, negatively charged, particles while the destination is an attracting, positively charged,particle. Extending the theory for weather and terrain/airspace will require to make distinctions in thequantity of charge for the various threats. Terrain will be a more negatively charged item than athunderstorm for example. Weather can consist of positively and negatively charged items. A tailwind areawill have, like the destination, a positive charge while thunderstorms, icing areas, clear air turbulence areaswill be negatively charged. So the voltage potential theory can be extended for weather and geographicalseparation. The same applies for the cross product theory, which can be used as one general resolutionmethod for the three separation functions with respect to separation. Making use of advantageous weatherphenomena like tailwind is not obvious however. Other, earlier discussed resolution algorithms have similardifficulties. For example, the extended VFR rules can be used for traffic but are not applicable for weatherand terrain. The extended VFR rules give priority to one aircraft over the other depending on the directionon which the two aircraft are closing in on each other. Priority rules, obviously, do not apply to weather,airspace and terrain. So, for weather, airspace and terrain a different separation algorithm has to bechosen. Having different separation algorithms might lead to a reduction of the crew awareness.

Detected conflicts with either traffic, weather, airspace or terrain will be alerted to the crew depending onthe level of urgency of the conflict. Urgency in this respect will depend on the time to occurrence of theconflict and the criticality of the conflict. The graphical presentation of these detected conflicts will bepresented in a display together with the threat. By presenting this it should be obvious whether this conflictis with traffic, weather, airspace or terrain.

Generally speaking, a resolution function will provide a resolution vector which will resolve the conflict usingthe separation algorithm rules. This resolution vector can be either lateral, vertical, in speed or acombination of these. For each of the resolutions apply that one is optimal, but other resolutions arepossible as well. The figures below present respectively the optimal and non-optimal lateral resolutions andvertical resolutions. For speed resolutions the same could be envisaged. In these figures, the optimalresolution is only optimal for traffic separation but taking weather and terrain into account as well, the non-optimal resolution might be the overall optimal resolution. This means that the separate resolution functionsshould provide not only the optimal resolution but one or more sub-optimal resolutions as well in order tobe capable of finding the overall optimal resolution, see figure 5 and 6. This process of finding the optimalresolution is a process in which all possible, resolutions are used for traffic, weather, airspace and terrainand together with the route of preference, the optimal resolution will be the result.Resolution algorithms regarding traffic which use strict rules allowing only one resolution for a certainconflict reduces the number of options and will most probably also result in less optimal overall resolution.

Figure 5 Lateral resolution in a single conflict situation: optimal solution and non-optimal



Figure 6 Vertical resolution in a single conflict situation: optimal solution and non-optimal solution

One overall condition has to be met however. A resolution manoeuvre should be easily understood by thehuman operator, the pilot. A graphical presentation of the manoeuvre in combination with the threats, eithertraffic, weather, airspace or terrain, will be helpful, but gives no guarantee. Given one or more threats, apilot should be able to predict roughly what the system will come up with as a solution of the problem. Itshould be avoided to present a solution to a certain situation which can hardly be understood by the pilot.Combining several resolutions under which non optimal ones might already lead to a confusing situationwhile combining several resolutions with a route of preference could result in even more complexresolutions. The latter should be omitted as much as possible when designing a new generation FMS. Adifficult to understand resolution leads to a loss of situation awareness and has a safety risk in it.

An example of a multi conflict situation is presented below with a combined lateral and vertical resolution.

Intruder aircraft

Storm cell

Terrain

Own aircraft

Lateral

Vertical

aircraft

terrainweather

Resolution

Resolution

Figure 7 multiple conflict situation with resolution

While operating in MAS, an ASAS equipped aircraft can be given responsibility to maintain separation withanother aircraft or to an aircraft approaching on a parallel runway. Only maintaining is foreseen, so de-conflicting and initial separating has already been done by ATC and the crew has the responsibility to carryout the instructed ASAS procedures (i.e. separation manoeuvre with a required separation performance, aperformance criterion the aircraft has to comply with).For station keeping procedures the complexity of the crew task depends on whether the route and/orprofile is pre-defined, for example as a 3D SID or STAR, or whether the preceding aircraft follows vectorsfrom ATC. In case the preceding aircraft follows the 3D SID or STAR, the crew task is to monitor deviations



from this 3D route by the preceding aircraft and to control their own speed so that the distance to thepreceding aircraft remains constant, or at least does not drop below the minimum value. In case thepreceding aircraft deviates from this 3D route, or is vectored by ATC, the crew task increases in complexity.Not only the longitudinal distance should be controlled now, but also the 3D path.The ASAS procedures, in which the aircraft has to maintain an ATC specified separation distance, mightbenefit from a separation manoeuvre function, for example in order to comply with ATC instructions forstation keeping, crossing, passing and merging procedures the aircraft automation could make use of afloating waypoint (a dynamic trajectory concept) defined by the separation zone of the other aircraft.

While approaching an airport with parallel runways which are both in use, the crew can be tasked tomonitor the traffic approaching on the runway parallel to the own runway. Monitoring in this sense is mainlyto detect deviation from other traffic in the direction of the own approach path. In case other traffic deviatestoo much and comes too near a go around should be initiated.

9.6 Route of Preference TasksIn the figure of section 9.5 two threats and one possible threat is indicated together with a combinedresolution. This resolution however has to be matched with the route of preference. Whether this matchbetween the possible resolutions and the route of preference is a parallel or sequential process will dependon the variations of the resolutions and the definition of the route of preference.The route of preference will most probably be based on a cost index, optimum vertical profile, multiplerequired time of arrival but more parameters can be foreseen.

9.7 Operational proceduresWhile operating in FFAS, two basic concepts for airborne co-operation are foreseen. Firstly, aircraft do notexplicitly co-ordinate to resolve the separation conflict, neither priority information nor intent information isco-ordinated. Both aircraft will manoeuvre according to the resolution algorithm. Any rule will beincorporated in the logical operations associated with these algorithms, for example both aircraft shall turnright in case of a head-on encounter when flying at exactly the same altitude.The operational procedure consist of the following rules (or equivalent ones):• no pilot-pilot communication• no pilot-controller communication• flight crew has to adhere to (one of the) resolutions generated by ASAS• flight crew has to react to separation cautions by means of executing resolution advisories within 2

minutes (between 5 and 3 minutes before predicted separation conflict)• flight crew has to react to separation warnings by means of executing resolution advisories immediately

(less than 3 minutes before predicted separation conflict)

Secondly, conflicting aircraft will explicitly co-ordinate who has priority, or in other words who has toperform the evasive manoeuvre and who has to adhere to the original plan of flight. So only one aircraftdeviates from its flight plan. The flight crew who has to give way may decide to follow the resolutionadvisories or may perform any other evasive manoeuvre as long as the conflict will be resolved.The operational procedure consists of the following rules (or equivalent ones)• priority of the own aircraft is determined according to the priority rules (e.g. FREER rules)• priority is co-ordinated between flight crews involved in the separation conflict (pilot-pilot

communication), the priority shall be agreed upon within 2 minutes.• flight crew who has priority must not change its flight plan until the separation conflict is resolved,

therefore must not manoeuvre in response to either separation cautions or separation warnings• flight crew who has to give way must react to separation cautions by executing a separation

manoeuvre within 4 minutes (between 7 and 3 minutes before predicted separation conflict)• flight crew who has to give way must react to separation warnings by executing a separation

manoeuvre immediately (less than 3 minutes before predicted separation conflict)• flight crew who has to give way must inform the other flight crews about the intended separation

manoeuvre.• flight crew who has to give way must inform the other flight crews when the conflict is resolved,

thereafter all flight crews regain the freedom to effect trajectory changes in any dimension.

While in MAS, the flight crew will have to comply with ATC instructions like in todays environment. Theadditional ASAS procedures in MAS do not fundamentally change the current working procedures.



The operational procedures for maintaining separation consist of the following events and actions (orequivalent ones):• receive ATC instruction (for example “PASS KLM602 LEFT AND MAINTAIN 04 NM SEPARATION”

or “FOLLOW KLM602 AND REDUCE SEPARATION TO 03 NM”)• respond to ATC instruction (“WILCO” or “UNABLE”)• activate applicable ASAS function and perform instructed manoeuvre• report, if applicable, when manoeuvre is completed (“BACK ON ROUTE”)

The operational procedure for monitoring separation is even simpler:• receive ATC request (for example “MONITOR KLM602 ON PARALLEL APPROACH”)• respond (“ROGER” or “NEGATIVE”)• inform ATC when other aircraft does not behave properly and, if deemed necessary, take safest course

of actions (e.g. go-around)

9.8 Modes of operationOperating in FFAS requires information from surrounding aircraft. Logical consequence is that surroundingtraffic requires information from its own aircraft. The amount of information which is required depends to alarge extend on the conflict resolution algorithm. The various algorithms require different information setsfrom surrounding traffic.

When ADS-B is used, it can be assumed that aircraft broadcast a/c state data and trajectory intent data1.The status of the trajectory intent data is included in the broadcasted a/c state data. A number of states ofthe trajectory intent data have been identified, the most important ones are lateral and vertical compliance.

In FFAS five different situations can be envisaged depending on crew selected FMS controlled autoflightmodes (LNAV, VNAV).a. Some aircraft do not broadcast ADS-B data; it is assumed that the ground will provide the a/c state

data set for these aircraft via TIS-B (note that the ground is responsible for separation assurance ofthese aircraft, being aircraft without ASAS/ADS-B)

b. Some aircraft do broadcast ADS-B data with trajectory intent status showing both lateral and verticalcompliance; indicating that the a/c adheres to both lateral and vertical FMS flight plan. (Expectednormal mode of operation).

c. Some aircraft do broadcast ADS-B data with trajectory intent status showing lateral compliance and novertical compliance; indicating that the a/c only adheres to the lateral FMS flight plan. (Temporarydeviation from FMS flight plan due to traffic or weather).

d. Some aircraft do broadcast ADS-B data with trajectory intent status showing neither lateral nor verticalcompliance; indicating that the a/c does not adhere to the FMS flight plan. (Temporary deviation fromFMS flight plan due to traffic or weather).

e. Some aircraft do broadcast ADS-B data without trajectory intent data, indicating that the trajectory isnot computed. Trajectory intent data can therefore not be broadcasted and the a/c is not adhering toan FMS flight plan. (Degraded mode of operation).

In FFAS it shall in principal be possible to operate aircraft with any of the five above-mentioned ADS-Bsituations. The allowable mix of the five is an open research issue. This operational requirement oninteroperability in FFAS and the availability of a common data set for each ADS-B situation results in thefollowing requirement: the basic ASAS functions should only depend on a/c state data as defined by RTCASC-186, possibly amended with other non-trajectory-intent data as required by the separation conflictdetection and resolution algorithms or the HMI. The baseline airborne separation functions should beadequate for normal operation.The availability of trajectory intent data may enhance or even optimise the ASAS functions. However, if thisdata is not available (from either ownship or other aircraft) then it should not result in a degraded airborneseparation function unsuitable for normal operation.Also for the own aircraft the mode of operation (i.e. LNAV and/or VNAV coupled operations) should notinfluence the functioning of the conflict detection nor conflict resolution advisory function.

1. For the moment the RTCA SC186 (MASPS for ADS-B, draft version 6.2) definitions of a/c state and trajectory intent data havebeen selected because they represent the initial data set that might be broadcasted by the aircraft.

9.9 Typical Flight



In this section an overview is given how a typical flight will be executed with an ASAS equipped aircraft inan environment existing of a combination of MAS and FFAS. Gate to gate operation will be considered.

Pre-flight phaseThe flight to be executed has been planned well in advance by the Airline Operations Control Centre (AOC)and Air Traffic Flow Management (ATFM) like in the current situation.AOC will provide the ATFM with an initial flight plan, this initial flight plan generated and optimised by AOCtakes account of expected congested areas, weather, terrain, airspace structure and company policies onfuel, connecting flights and other cost and time related issues.

ATFM plans a number of flights which will not exceed runway capacity on the departure airport, airspacecapacity between departure, destination and alternate airport and runway capacity on the destinationairport.ATFM will provide to AOC an initial departure time (i.e. take-off slot) and, if capacity problems are notsolved through the take-off slot, they also might provide a required time of arrival (for example landing slotor flow management slot at MAS entry point). In a process of negotiation AOC and ATFM will come to anagreement and an ATC flight plan will be the result. (AOC and ATFM would benefit from the RoPalgorithms developed in 3FMS (these are currently made available to AOCs)).

One hour (for European flights) before push back the flight crew will be briefed by AOC. The dispatcher willbrief the flight crew on the planned flight, this includes the ATC flight plan, airspace structure andrestrictions, weather forecast, NOTAMs, a/c loading, fuel planning, company policies, etc.

The aircraft has arrived at its parking position at the assigned gate following completion of the previousflight.The data required for FMS flight planning, including airspace structure and significant weather data will betransmitted by the flight crew from Airline Operations Control Centre to the aircraft via data link.Ground engineers will, if necessary, take care of the on-board loading of the navigation and terrain databases.

Preparation phase35 minutes before push back the flight crew will enter the cockpit and as part of the cockpit preparationthey will initialise the FMS for the flight. This means that flight plan data, initial loading data, company policydata and wind/temperature data will be inserted, by loading of uplinked data. The terrain, airspacestructure, significant weather and navigation data bases will be checked for validity. Subsequently theplanned route will be checked against the above-mentioned data bases. Since AOC provided the routeusing the same data bases (or more extensive versions of them) this should not provide any inconsistency.

Before Starting and Before Taxi phaseAfter delivery of the load sheet and LMC (last minute change) notification the FMS initialisation will becompleted, e.g. final weight and balance data from the load sheet will be uploaded by AOC via data link.

Since both origin and destination airport are part of MAS, and ATC has active control in MAS, the crewrequests a route clearance and engine start-up clearance.After having received the start up clearance, being the clearance which includes the take-off slot, thestarting engine sequence will be executed and subsequently the push back clearance is requested. Afterpush back, the taxi clearance will be requested.

The route clearance will be provided by ATC either before, together with or after the start-up clearance.This clearance might even be given during the taxi-out phase. The route clearance will permit the aircraft tofly to its destination airport, normally via the agreed ATC flight plan, and will provide the take-off runway anddeparture procedure in use. A flow management slot for entering MAS from FFAS might also be part of theroute clearance. All these requests and clearances will be exchanged via data link (CPDLC message set).After receipt the crew will check and insert the data in the FMS.

Taxi Out phaseTaxi clearances will be received via data link, possibly accompanied with changes in take-off runway, take-off slot and departure procedure. The crew will now taxi to the take-off runway aiming to arrive in timebefore the allocated take-off slot time using the taxi route as included in the taxi clearance. The taxi supportsystem will support the crew not only in navigating on the airport but also to reach the runway in time.

Take-off and Initial Climb phaseATC will provide a take-off clearance by data link or R/T. The crew will line up and perform the take-off.After take-off the initial climb out will be performed taking into account the standard instrument departure



(SID) which was cleared by ATC, or tactical instructions from ATC will be followed by the crew. For thesephases no major difference exist compared to existing take-off and initial climb out procedures, only datalink replaces the R/T and ASAS procedures like station keeping, passing and crossing are operational.

Climb phaseDuring the climb the boundary between MAS and FFAS will be crossed, ATC will notify the crew via datalink that they are entering FFAS and leaving MAS and will transfer separation authority to the flight crew.This means that active involvement of ATC stops at that moment, though it should be kept in mind that re-entry into MAS, in terms of location and ETA (or RTA), is already planned by means of the ATC flight plan.However still there is contact with ATC required in exceptional cases, for instance because during the flightin FFAS, the re-entry conditions change either air-initiated or ground initiated.Now the crew entered FFAS, it is necessary to contact another ATCo and for that reason the R/Tfrequency will need to be changed. This frequency change can be either initiated via data link or via R/T.In case the controlled flight through MAS has deviated the aircraft from the initial planned route (i.e. theroute of preference based on the ATC flight plan) the crew will return to this ROP, or let the FMS re-calculate the ROP.The climb is performed relatively soon after the data bases are uploaded at the gate and the route hasbeen determined using these data bases. For this reason the route will not be required to be modified dueto significant weather, congested airspace, terrain and airspace structure. In case of a delay at thedeparture airport the data bases, if deemed necessary by AOC (or FIS ?), will be updated via data link anda new route of preference will be calculated. This new ROP will have to comply with the known traffic flowrestrictions and ATC route clearance. Therefore if the take-off is delayed a further route modification duringclimb, due to weather, congestion, terrain or airspace structure, will not be required.With respect to traffic the situation is different. In case a conflict has been detected with an other aircraft,the crew will be alerted and the conflict will be presented on the traffic display. What follows depends onthe rules of the air which apply. Since no decision has been taken yet with this respect, two possiblescenarios (although more can be envisaged) will be described here.

Scenario 1: One aircraft manoeuvres - explicit co-operationBoth aircraft involved in the conflict will have detected the conflict. Based on the flight rules (for examplethe Extended Flight Rules as developed by FREER) one of the two aircraft will have priority over theother. While these rules are known to both aircraft, both aircraft will determine which of the two haspriority. When both aircraft have determined who has priority, this will be acknowledged by means ofair-air co-ordination via air-air data link, or by R/T. The aircraft which has priority is now required tomaintain its current a/c state vector and, depending of the mode of operation (i.e. LNAV and/or VNAVcoupled flight), to adhere to its route of preference, while the other aircraft initiates an evasivemanoeuvre to resolve the conflict. This evasive manoeuvre might be based on resolution advisories ascalculated by the separation algorithms (for example algorithms based on potential forces, modifiedvoltage potential or genetic optimisation). Once the conflict has been resolved, both aircraft will be freeto follow their (new) route of preference again. The manoeuvre to be taken in order to resolve theconflict is not defined by rules, so the crew can initiate any manoeuvre resolving the conflict as long asthe separation minima are not exceeded.

Scenario 2: All aircraft manoeuvre - implicit co-operationAgain both aircraft involved in the conflict will detect the conflict. The conflict will be presented to crewon the traffic display. The way the conflict is presented encompasses resolution advisories leadingimmediately to the smallest manoeuvre to solve the conflict either laterally or vertically. Note that theresolution advisories will be calculated by the separation algorithms (for example based on potentialforces or cross product of speed vectors). The manoeuvre will be sufficient to solve the conflict eventhough the other aircraft is not taking any action. The other aircraft however is confronted with the samesituation and will initiate a manoeuvre as well. Once the manoeuvre of the other aircraft has beendetected and observed, the conflict decreases and the manoeuvre can be decreased as well, stillsolving the conflict. Since both aircraft are manoeuvring, the magnitude of the manoeuvre is limited.

After the conflict has been resolved, the crew will return to the ROP, or a new ROP will be calculated fromthe current position. In case a new ROP is to be calculated, it will be checked against (or calculated using)the significant weather, terrain and airspace structure data bases.

En-route phaseThe transition from the climb phase to the en-route phase is determined by the ROP based on the optimalflight profile.For medium and long haul flights, the validity of the weather data base (and perhaps also the airspacestructure data base) decreases and a new data base, or parts of it, will be uplinked by AOC (or FIS ?) viadata link. The crew will be notified about the fact that a new data base has been received. The crew nowinitiates a new calculation of the ROP based on the new data, or the system proposes automatically a newROP after reception of a data base update.



Sectors that are most likely much larger than the current ones are required for the ATCo to perform histasks in FFAS. While in the en-route phase, several sectors will be crossed and on each sector boundarythe R/T frequency will have to change. Data link might be used to initiate this, otherwise the current daypractice will be used.

As for the climb phase traffic separation conflicts will occur and need to be resolved by the crew withassistance of the on-board ASAS functions.Furthermore, with the passage of time, forecasts of significant weather may become inaccurate. As aconsequence a separation conflict with actual weather may occur, the detection and resolution method issimilar to the traffic separation case with the constraint that only the aircraft is capable of detecting andresolving these type of separation conflicts.

In case of abnormal or emergency conditions, requiring urgent changes in the flight plan (e.g. emergencydescent, land at closest airport) or requiring all the support of ATC to reduce peak workload, the crew willcontact ATC by R/T and request assistance. ATC takes separation authority, gives instructions to the crewin trouble and informs crews in the neighbourhood of the aircraft in trouble. In conjunction the aircraft introuble may transmit ADS-B messages that include flags set to indicate their situation and actions (e.g.abnormal/emergency condition, emergency descent, ATC controlled flight).

Pre-descent phaseTop of descent is determined by the ROP. This top of descent has been calculated so that the optimal (intime, fuel or cost) descent can be performed towards the entry point (including altitude) of the MAS. ThisMAS entry point is defined by the airspace structure data base and, in case the position is changed (closerto the runway due to low traffic densities for example) AOC (or FIS ?) will update the airspace structuredatabase as already described in the en-route phase.Well before starting the descent (approximately 200-150 NM or 40-30 min from touchdown), ATC willquery for the desired time of arrival over the planned MAS entry point, or new MAS entry point if instructedby ATC, and the pilot will respond with the FMS solution. ATC will subsequently fit the aircraft in thesequence of arriving traffic and in order to do so ATC will indicate to the crew an (update of the) RTA at theMAS entry point together with a required speed to maintain at that entry point. (On the one hand, the MASentry point and the RTA should be known sufficiently in advance: ideally at the departure airport. The MASand RTA define the “destination” as far as the RoP is concerned. On the other hand, the schedulingshould not be frozen so early that arrivals from nearby airports often disrupt the scheduling process.)

Descent phaseDuring the descent in FFAS the aircraft will have to resolve separation conflicts with other traffic andunanticipated movements of significant weather.The detection and resolution method will be identical to methods used during climb and en-route phases offlight.

Final Descent and Approach phaseBy the time the aircraft is entering MAS by crossing the entry point, ATC will take full control by transferringseparation authority and subsequently giving vectors or clearing the aircraft for a STAR maintaining aspecified speed. Instead of giving the aircraft speed clearances and vectors, ATC is also able to clear theaircraft to follow the preceding aircraft at a certain distance (or time) along the STAR. The only remainingair-ground communication is to reduce the separation distance when closing in to final approach. Thecrossing, passing and merging procedures will be used by ATC in suitable situations.During the final descent phase the approach will be prepared, encompassing setting up or checking theapproach procedure in the FMS. Hereafter, it still might be necessary to update the approach procedure,i.e. in case the assigned landing runway is changed.

After receipt of the approach clearance and when established on final approach the role of the FMSperforming the flight path management task is being taken over by the Multi-Mode Receiver using ILS,MLS or GLS. Only after vacating the landing runway the taxi support system will be used again.

Landing phaseATC will give a landing clearance. In case two parallel runways are in use, ATC can request the crew tomonitor the traffic on the parallel runway while on the approach path.

Taxi In phaseAfter vacating the landing runway ATC will provide taxi clearances indicating the destination (gate) and thetaxi route to be used. If possible ATC will give instructions to follow a preceding aircraft until a certain point.

After Parking phaseThe parking position is reached and the engines will be shut. If not already done shortly before reaching thegate the R/T and data link communication with ATC will be terminated.



Abbreviations

3FMS Free Flight FMS4D Four DimensionalACARS Aircraft Communication And Reporting SystemADS Automatic Dependent SurveillanceADS-B Automatic Dependent Surveillance - BroadcastAOC Airline Operations CentreASAS Airborne Separation Assurance SystemATC Air Traffic ControlATCo Air Traffic ControllerATFM Air Traffic Flow ManagementATM Air Traffic ManagementATN Aeronautical Telecommunication NetworkATS Air Traffic ServiceCDTI Cockpit Display for Traffic InformationCPDLC Controller Pilot Data Link CommunicationCTAS Center TRACON Automation SystemDA Descent AdvisorDG XII Directorate General 12EATMS European Air Traffic Management SystemETA Estimated Time of ArrivalETMA Extended Terminal Manoeuvring AreaEVFR Extended Visual Flight RulesFANS Future Air Navigation SystemFFAS Free Flight AirspaceFIS Flight Information ServiceFMS Flight Management SystemGPWS Ground Proximity Warning SystemHMI Human Machine InterfaceLNAV Lateral NavigationMAS Managed AirspaceMCDU Multi function Control and Display UnitOCD Operational Concept DocumentRNP Required Navigation PerformanceRoP Route of PreferenceR/T Radio TelecommunicationRTA Required Time of ArrivalRTCA Radio Technical Commission for AeronauticsSAE Society of Aeronautical EngineersSID Standard Instrument DepartureSTA Scheduled Time of ArrivalSTAR Standard Arrival RouteTCAS Traffic Collision Avoidance SystemTCP Trajectory Change PointTIS-B Traffic Information Service BroadcastTMA Terminal Manoeuvring AreaTMA Traffic Management AdvisorUAS Unmanaged AirspaceVFR Visual Flight RulesVNAV Vertical Navigation



References

Reference General Separation ResponsibilityATCo, in Managed Airspace ATCo/Flight Crew, in Managed

Airspace;Separation responsibility partiallydelegated by ATCo (typically pair-wise application for equipped a/c)

Flight Crew, in Free Flight Airspace;Separation responsibility fullytransferred to the aircraft

Alliott, J.M., Gruber, H. andSchoenauer, M. (1993). ‘UsingGenetic Algorithms for Solving AirTraffic Control Conflicts’, inProceedings of the NinthConference on ArtificialIntelligence Application. Orlando,FL: IEEE.

ATC based problem solvingalgorithms for strategic flightplanning.Classical Genetic Algorithmsused.Changes in heading, altitude andspeed.Off line computer simulation.Number of required iterationsteps as main parameter.

Off line computer simulation.Genetic algorithms described in paperfor ATC problem solving in currentATM environment but might be usedfor ASAS conflict resolutionalgorithm.

Avans, D. and Smith, K. (19…).Experimental Investigations ofPilot Workload in Free Flight’.Human Factors ResearchLaboratory, University ofMinnesota, …..

Airborne problem solvingexperiment.3 Traffic scenarios:Crossing a/cA/C converging to pathOvertaking a/c6,11 or 16 a/c in scenario0°, 45° and 90° relative heading

Experiment in simulated 757 glasscockpitND depicting other a/c in the airspaceand colour coded proximity warning.MCDU with 3 toggle buttons forlateral and vertical manoeuvreoptions and a/c status info.

Aveneau, C. et al (1997).‘Feasibility Assessment of SelectedADS-B/ASAS Applications and

Identification of generic issues(operations, procedures,requirements…) in the

LSK & CSPA: ATC monitors andprovides clearances.Contracts between pilots and ATC.

AA: ASAS, but ATC monitors traffic,controls entering, exit and number ofa/c in FFAS and provides (long term)






Users’ Interview’.EMERALD/WP5/SOF/010/1.0,Version 1.0, EMERALD.

assessment of 3 operationalscenarios:Longitudinal Station Keeping(LSK)Closely Spaced ParallelApproaches (CSPA)Autonomous Aircraft (AA)Using ADS-B + CDTI

traffic info to a/c.

Ball, J.W. Sr. (1997). ‘Free Flightan Air Traffic ManagementPartnership.’ Lockheed MartinA.S. in Proceedings of the 16th

Digital Avionics SystemsConference: AIAA and IEEE.

Collaborative automation forATC, AOC and flight deck usingATN.Several levels of equipage,highest level is self separating.Decision aiding tool for Atco,especially for mixed equipage.Including CTAS for enteringTMA.Conflict resolution algorithmsdefined but not explained in thispaper.

Off line simulation.

Brudnicki, D.J. and McFarland,A.L. (1996). ‘User RequestEvaluation Tool (URET) ConflictProbe Performance and BenefitsAssessment’. CAASD, The MITRECorporation, MP97W0000112.McLean, VA.






Brudnicki, D.J., Lindsay, K.S. andMcFarland, A. L. (1997).‘Assessment of Field Trials,Algorithmic Performance, andBenefits of the User RequestEvaluation Tool (URET) ConflictProbe’, in Proceedings of the 16th

Digital Avionics SystemsConference: AIAA and IEEE.

Conflict probe on the groundusing ARTCC data (flight planand radar data).Main topic is the development ofa decision aiding tool in case of aconflict.

Field trials were conducted usingreal traffic data as input.

Casaux, F. and Hasquenoph, B.(1997). ‘Operational Use ofASAS’, in First USA/Europe AirTraffic Management R&DSeminar, Saclay, France:EUROCONTROL and FAA.

Free Flight vs. ASAS vs. AAOperational concept of ASASCrossing Procedure

Temporary delegation of separationresponsibility to the pilot by means ofcontracts regarding a certain object(the crossing) and duration.Paper study, based on: crossing trafficat 90°, ownship ASAS equipped andclimbing or descending, conflicttraffic is level.

Duong, V.N. (1996). ‘DynamicModels for Airborne Air TrafficManagement Capability: State-of-the-Art Analysis’. EEC Report No.xxx, EUROCONTROLExperimental Centre, Brétigny-sur-Orge, France.Duong, V. N. et al (1996).‘Extended Flight Rules (EFR) toApply to the Resolution ofEncounters in Autonomous

Review of Visual Flight Rules(VFR) and ATLAS AutonomousFlight Rules (AFR)Detailed description of Extended

Autonomous mode of operation inlow density traffic situation.Following issues are considered- a/c priority categories






Airborne Separation’.EEC/ATM/FSA/R11-96-03,EUROCONTROL ExperimentalCentre, Brétigny-sur-Orge, France.

VFR rules (EFR, priority rules).Advantages of EFR over VFRand AFR. Goal is to identifywhich a/c must take the evasiveaction when an encounter occurs,and when the action must bemade

- all phases from take-off untillanding- manoeuvrabilityof a/c- navigation constraints- number of a/c involved in encounter- distance to encounter- different equipped a/c (IFR, EFR, ..)

Duong, V. N., Hoffman, E. andNicolaon, J.P. (1997). ‘InitialResults of Investigation intoAutonomous Aircraft Concept(FREER-1)’, in First USA/EuropeAir Traffic Management R&DSeminar, Saclay, France:EUROCONTROL and FAA.

See Duong, V.N. (1997).

Duong, V.N. and Hoffman, E.G.(1997). ‘Conflict ResolutionAdvisory Service in AutonomousAircraft Operations’, in Proceedingof the 16th Digital Avionics SystemsConference: AIAA and IEEE.

See Duong, V.N. (1997).

Duong, V.N. (1997). ‘FREER:Free-Route ExperimentalEncounter Resolution - InitialResults’, in in Proceedings of the10th European AerospaceConference Free Flight (pp. 9-1 -

ASAS in low density trafficsituation.Rules of the sky: extended VFRrules (priority rules).AOC involved in planning phase.ATFM involved.

FREER 1: full ASAS but only en-route and low density.FREER 2: partial ASAS when highdensity traffic.Flight simulator experiment:CDTI






9-12). Amsterdam, TheNetherlands: Confederation ofEuropean Aerospace Societies.

Concentrating on En-route. Conflict detection: presenting no gozones.Conflict resolution: Extended VFR,in 3 levels: manual, semi automaticor automatic.

Durand, N., Alliott, J.M. andChansou, O. (1996). ‘OptimalResolution of En Route Conflicts’.Air Traffic Control Quarterly, Vol.3(3), pp. 139-161.

See Durand, N et al (1994).

Durand, N. et al (1994). ‘GeneticAlgorithms for Conflict Resolutionin Air Traffic’, in Proceedings ofthe Second Singapore Conferenceon Intelligent Systems, Singapore:SPICIS.

ATC based algorithms.Preferably lateral maneuvers, ifvertical maneuver is required, norate of climb/descent is dictated.Genetic algorithm starts with‘random’ solution and iterates tooptimal solution.Classical genetic algorithms areused.

Off line computer simulation: conflictinvolving 5 aircraft.Genetic algorithms described in paperfor ATC problem solving in currentATM environment but might be usedfor ASAS conflict resolutionalgorithm.

Durand, N., Alliot, J.M. andNoailles, J. (1996). ‘AutomaticAircraft Conflict Resolution UsingGenetic Algorithms’, inProceedings of the ACM/SAC ’96Conference, Philadelphia, PA:ACM

Mathematical modeling of enroute conflict resolution,horizontal plane only. Solverdesign as close to current ATC aspossible.

Off line simulations.Traffic simulator , using real trafficdata as inputPair wise conflict detection andclusteringProblem solver using ‘turning point’or ‘offset’ solutions

Eby, M.S. (1994). ‘A Self-Organizational Approach for

Self organisational means selfseparation.

Off line simulation.Conflict resolution algorithm for






Resolving Air Traffic Conflicts’.The Lincoln Laboratory Journal,Vol. 7, No.2.

Modified Potential Field modelused for conflict resolution.Main emphasis: this conflictresolution in airborne side incomplex traffic situations.

faster and more efficient problemsolving.

Endsley, M.C. (1997). ‘SituationAwareness, Automation and FreeFlight’ in First USA/Europe AirTraffic Management R&DSeminar, Saclay, France:EUROCONTROL and FAA.

FF impact on ATC: awarenessproblem due to automation.Controller will get the role ofarbiter. And needs tools forunexpected aircraft movements.

Simulation experiment with ATCo’s,no pilots.ATCo intervenes as arbiter only.

EUROCONTROL (1997a). ‘ATMStrategy for 2000+’. Version 1.0.

Description of the proposed ATMstrategy for 2000+ that will meetEurope’s air transport needs outto 2015, together with a roadmapfor change based on theprogressive introduction of anumber of operationalimprovements over time.

2005-2010: limited transfer ofseparation responsibilities fromground to air; pilot is responsible forseparation in some definedcircumstances in suitably equippedaircraft (early introduction of ASAcapabilities with improved situationawareness displays).

2010-2015: introduction ofautonomous a/c operations; pilot isresponsible for maintaining ownseparation in designated free flightairspace using ASAS.

EUROCONTROL (1997b).‘EATMS Operational ConceptDocument’, Issue 1.0.

High level scenario descriptionincluding migration plan from2000 to 2015.Starts with free routing, final goalis full free flight from gate togate.

Final stage consists of full ASASequipped aircraft from gate to gate.

FANG (1996). ‘FANG Operational Definition of the future integrated Envisioned services for 2000+ Envisioned services for 2000+






Concept’. Flight ManagementSystem - Air Traffic ManagementNext Generation (FANG).

ATM/FMS/AOC requiredfunctional and operationalcapabilities, associated servicesand system architecture.ATM responsible for settingseparation requirements.Responsibility of assurance couldbe delegated to the air based uponboth ground and airborne conflictprediction and resolutioncapabilities.CTAS will be centerpiece ofterminal automation

(related to separation assurance)• User preferred trajectories - pilot will be permitted to

manoeuvre at will withoutcontroller intervention until thealert zone overlaps another alertzone, the controller will thenintercede and resolve theconflict

- separation assurance remains withthe controller

(related to separation assurance)• Offset passing - pair-wise separation - air-air/air-ground procedures• Self separation (station keeping) - relative to the aircraft ahead• Merging and relative guidance - relative to the aircraft ahead - after verification that each aircraft

will meet the RTA’s

Gent, R.N.H.W. van, Hoekstra,J.M., Ruigrok, R.C.J. (1997). ‘FreeFlight with Airborne SeparationAssurance’, in Proceedings of the10th European AerospaceConference Free Flight (pp. 35-1 -35-17). Amsterdam, TheNetherlands: Confederation ofEuropean Aerospace Societies.

FF concept for en-route operationin the upper airspace is designedin detail.• rules-of-the-sky• conflict resolution algorithm• conflict detection algorithm• cockpit display

recommendations• system description• operational implications

En-route operationsOff-line computer simulation,comparing conflict resolutionmethods• altitude step• cross product of speed vectors• extended VFR rules• variations on TCAS maneuvers• different implementations of

voltage potentialSafety analysis comparing• modified voltage potential

resolution method• current day ATCPiloted simulation experiment






• three automation levels of conflictresolution execution

• three levels of traffic density• eight airline crews

Hansman, R.J. et al (1997).‘Integrated Human CenteredSystems Approach to theDevelopment of Advanced AirTraffic Management Systems’ inFirst USA/Europe Air TrafficManagement R&D Seminar,Saclay, France: EUROCONTROLand FAA.

Human centred system designapproach.Humans (pilots and ATCo’s) arepart of ATM system.

Simulation experiment focusing onCDTI with 4 levels of informationpresented on CDTI.Simulation experiment with ATCo’s.(Probably not the same exp.)

Hilburn, B.G., et al (1997). ‘TheEffect of Free Flight on Air TrafficController Mental Workload,Monitoring and SystemPerformance’ in Proceedings of the10th European AerospaceConference Free Flight (pp. 35-1 -35-17). Amsterdam, TheNetherlands: Confederation ofEuropean Aerospace Societies.

Tool support for ATCo in FFenvironment. Extended flightrules are used.STCA available: ATCo shouldtake action only when STCA alertoccurs.

ATC simulation experiment. 3conditions were tested:• ATC managed• FF, pilot informs ATC• FF, pilot does not inform ATCWorkload measurements taken fromATCo’s.

Hoekstra, J.M., Gent, R.N.H.W.van and Ruigrok, R.CJ. (1998).‘Conceptual Design of Free Flightwith Airborne SeparationAssurance’. To be published.

Not available.






Krella, F. et al (1989). ‘ARC 2000Scenario’. EEC Technical Note No.6/89, EUROCONTROLExperimental Centre, Brétigny-sur-Orge, France.

Automatically managed airspace:take the human out of the loop.A ground system solves allproblems and uplinks via datalink resolutions to the aircraft.Outside automatically managedairspace also ATC controlledairspace exists.

Scenario description, no simulation:automatically managed airspace.

Krozel, J., Mueller, T. and Hunter,G. (1996). ‘Free Flight ConflictDetection and Resolution Analysis’in Proceedings of GuidanceNavigation and ControlConference, AIAA-96-3763, SanDiego, CA: AIAA.

Free Flight support for ATC andPilot. Advisory system notifiesAtco and pilot.ATC in passive control untilconflict detected, then ATC takescontrol to solve problem.Situation exists above certain FL,stepwise introduction would be toreduce this FL.Including CTAS for MASentering.Conflict resolution: ATC usesEuler-Lagrange equations foroptimal solution in lateral,vertical and speed.

Off line simulation.Aircraft are free to manoeuvre untilATC detects conflict, ATC solvesconflict, after conflict aircraft are freeto manoeuvre again.

Lozito, S. et al (1997). ‘Free Flightand Self-Separation from the FlightDeck Perspective’, in FirstUSA/Europe Air TrafficManagement R&D Seminar,

Airborne separation, but ATC hasthe final responsibility. Based onRTCA.Using ADS-B with CDTIUsing air and ground tools.

Flight simulator experiment:• 10 crews• 2 traffic density levels• 4 scenarios (types of conflicts)






Saclay, France: EUROCONTROLand FAA.

Conflict resolution: VFR rules.Communication between aircraftfor co-ordinated conflict solving.

Mundra, A. et al (1997). ‘PotentialADS-B/CDTI Capabilities forNear-Term Deployment’, in FirstUSA/Europe Air TrafficManagement R&D Seminar,Saclay, France: EUROCONTROLand FAA

Near term introduction of CDTI.Mainly for enhanced visualapproach to increase runwaycapacity.Oceanic: station keeping andintrail climb and descent.

Mid fidelity flight simulatorevaluation for parallel runwayapproaches using a CDTI.

Paielli, R.A. and Erzberger, H.(1997). ‘Conflict ProbabilityEstimation for Free Flight’.Journal of Guidance, Control andDynamics, Vol. 20, No. 3, pp. 588-596.

Mainly aiming at conflictdetection using trajectoryprediction on the ground.Tool for ATCo’s, taking care ofaircraft pairs in FF environment.

Off line simulations with MonteCarlo method. Variations incrossing angle and time to minimalseparation.

Pritchett, A.R. and Hansman, R.J.(1996). ‘Experimental Study ofCollision Detection Schema Usedby Pilots During Closely SpacedParallel Approaches’. GuidanceNavigation and ControlConference, AIAA 96-3762, SanDiego, CA: AIAA.

Approach only.Parallel approaches with conflictdetection and resolution by pilotusing a traffic display.No specific resolution algorithmsused.

Flight simulator experiment:• 5 traffic displays• 4 scenarios• 2 workload levels

Pujet, N. and Feron, E. (1996).‘Flight Plan Optimization inFlexible Air Traffic Environments’.

Flight plan optimisation by AOCin FF environment. Taking intoaccount weather, congested

Off line simulation for user preferredroute optimisations.






Guidance Navigation and ControlConference, AIAA 96-3765, SanDiego, CA: AIAA

airspace, restricted areas andRTA.Strategic solution (4D corridor)from AOC uplinked to aircraft.Aircraft is autonomous incorridor, when outside corridor,contact AOC. ATC providesadvisories.Self separating, conflict detectionand resolution not explained.

RTCA (1994). ‘Report of theRTCA Board of Directors’ SelectCommittee on Free Flight’. RTCAInc., Washington, DC.

Includes FF definition.FF includes: people, proceduresand technologies.ATFM (air traffic flowmanagement) included.Automation to be used to supportpeople, not replace them.TMA entering: use CTAS.Conflict probing tools requiredfor ATC.

Includes transition tables includingrequired ATC and A/C capabilities.

RTCA (1995). ‘Final Report ofRTCA Task Force 3: Free FlightImplementation’. RTCA Inc.,Washington, DC.

Free Flight definition.Protected zone and alert zone.ATFM is assumed.Aircraft should be equipped forASAS.

If partial ASAS, both controller andpilot should fully aware of controldelegation to the pilot.

Final goal is ASAS.ASAS, but still ATC verifiesseparation: arbitration function.

RTCA (1997). ‘Minimum AviationSystem Performance Standards for

Increasing ASAS. Starting withbasic FF functions and aiming at

CDTI with basic functions: in trailclimb, in trail descent, passing and

Migrating to full ASAS. However itis expected that the ADS-B messages






Automatic Dependent SurveillanceBroadcast (ADS-B)’. Draft 5.0,prepared by RTCA SpecialCommittee-186.

full ASAS.Conflict detection.Conflict solving: VFR rules.CDTI fed by ADS-B, TCAS andFIS.

station keeping.Oceanic, en-route and non radarenvironments.

require extension.

SAE (1997). ‘Human FactorsIssues in Free Flight’. DraftAerospace Resource Document(ARD), SAE G-10 AerospaceBehavioral EngineeringTechnology Free FlightSubcommittee.

Human Factors in FF: 22 itemslisted.Recommended implementationapproach.Self separation: traffic + weather+ terrain.Since FF not yet defined, so whenscenario defined, a task analysisrequired for the pilot’s task.

Simulation recommendations:Full fidelity simulator experimentshould be conducted.Pilot’s workload should not becomputer simulated.Use real pilots and real ATCo’s.

Scallen, S., Smith, K. andHancock, P. (1996). ‘Developmentof a Simulator to Investigate PilotDecision Making in Free Flight’.SPIE, Vol. 2740, pp. 68 -76

ASAS:conflict detectionconflict resolution: standardrules, applied by the pilot.

Simulator experiment.• Traffic density (3 levels)• Traffic mix (3 levels)• Bearing with own a/c (5 levels)• Type of conflict (6 levels)28 out of these 270 were simulated.Resolutions: lateral and vertical.

Sharkey, S. (1997). ‘Towards anOperational Scenario for StationKeeping’. SICASP/WG2,WP2/648, Hawaii.

Pairwise ASAS: station keepingin a master-slave situation. ATCmanages a stream instead of allindividual aircraft. ATC sectorsstill exist. Comfort and economyproblems foreseen.

No simulation. ATC manages trafficstream. Use of ADS-B and CDTI.






Vermeij, J. et al (1997a).‘Assessment of the Impact of theRNP Concept on ATM’. DraftVersion 0.1, EMERALD.

The RNP concept prescribesimproved navigational accuracyon any desired flightpath. 4DRNP is expected to precede fullFF.

Warren, A. (1997a). ‘AMethodology and Initial ResultsSpecifying Requirements for FreeFlight Transitions’ in FirstUSA/Europe Air TrafficManagement R&D Seminar,Saclay, France: EUROCONTROLand FAA.

FF transitions examined.ATC tool for FF environment toallow user preferred routing.Reduction of separation minimausing future CNS ATMequipment.

Off line simulations using MonteCarlo method

Warren, A. (1997b). ‘MediumTerm Conflict Detection for FreeRouting: Operational Concepts andRequirements Analysis’, inProceedings of the 16th DigitalAvionics Systems Conference:AIAA and IEEE.

En route only. 10-30 min lookahead. Free routing. Conflictdetection and resolution by ATC.Uses intent info, radar data, ADSand wind info.Three methods of detectionexamined.Goal: minimise ATC interventionin free routing situation.

No simulation. ATC manages freerouting situation. Efficiencyincrease is main goal.

Yang, L.C. and Kuchar, J.K.(1997). ‘Prototype ConflictAlerting System for Free Flight’.Journal of Guidance, Control andDynamics, Vol. 20, No. 4, pp. 768-773.

Mainly concentrated on conflictdetection using several alertingstages.Resolutions of conflict are co-ordinated with other aircraft iftime allows. In case no time

Part of NASA (Ames) flightsimulator experiment.Monte Carlo method used.Pilot gets tool to evaluate severalpossible resolutions.






available, ATC will provide aresolution.

Zeghal, K. (1997). ‘AirborneConflict Detection and Resolutionusing Coupled Forces FieldTechnique: Principles and Results’.AGARD Workshop, Budapest.

ASAS using ADS-B. Conflictdetection and resolution.Resolution based on potentialforces and sliding forces. Slidingforces for moving around anobstacle/aircraft.

Off line simulation based on MITREmodel of encounters in FF situation.



Appendix: Definition of ADS-B Report

ADS-B report (defined by RTCA SC-186 - MASPS for ADS-B. draft version 6.2)Call sign

• 7 alphanumeric charactersAddress

• ICAO 24 bit addressCategory

• as defined by ICAO, for example ‘Heavy aircraft - 136,000 kgs or more’State vector

• latitude• longitude• barometric altitude• geometric height• north-south velocity• east-west velocity• barometric altitude rate• geometric altitude rate• airborne turn indication• navigation uncertainty category - position• navigation uncertainty category - velocity

Status and intent information• emergency/priority status• current trajectory change point (TCP)

⇒ latitude⇒ longitude⇒ pressure altitude⇒ time to go

• trajectory change point + 1 (TCP+1)⇒ latitude⇒ longitude⇒ pressure altitude⇒ time to go (from now)

Class code• indication of capability to support engagement in specific operations

Other information• requirements for applications not specifically identified in current MASPS

free flight - flight management system brite/ euram project filefree flight - flight management...

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