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Project EMERALD Work Package 5

Ref. : EMERALD/WP5/SOF/015/1.0Version 1.0 produced on 12 March 1998

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Assessment of emerging technologies: the specific caseof ADS-B/ASAS

Assessment of emerging technologies: the specific case of ADS-B/ASAS 12 March 1998EMERALD/WP5/SOF/015/1.0 Version 1.0

Principal Authors

Name Francis CASAUXAppointment CENALocation Toulouse, FranceTelephone +33 5 62 25 95 24

Name Dr Ken CARPENTERAppointment DERALocation Malvern, UKTelephone +44 (0)1684 894771

Name Sarah SHARKEYAppointment NATSLocation LondonTelephone +44 (0)171 832 6259

Name Pascal DIASAppointment ThomsonLocation BagneuxTelephone +33 (0)1 40 84 15 16

Name Gérard SAINTHUILEAppointment SextantLocation Vélizy-VillacoublayTelephone +33 (0)1 46 29 71 81

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Record of changes

Issue Date Detail of Changes

1.0 12 March 1998 Initial version

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Abstract

This report describes the key results from EMERALD Work Package 5. It summarises a study of ASAS applications and an assessment of the suitability of ADS-B techniques for the development of ASAS applications.

It also contains details of a comprehensive Research and Technical Development plan which outlines the key issues and actions required to further develop the ASAS applications. The timescales for this work are estimated as within the EATMS timescales for the development of ‘Co-operative ATM’.

Finally, it provides recommendations to carry out further research based on the RTD plan, with co-ordination from all interested parties.

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Table of contents

1. INTRODUCTION...................................................................................................................................................

1.1.1 WP5 Ojectives..................................................................................................................................................1.1.2 Involved partners..............................................................................................................................................1.1.3 WP5 tasks.........................................................................................................................................................1.1.4 WP5 effort and schedule...................................................................................................................................1.1.5 Internal WP5 deliverables................................................................................................................................1.1.6 External WP5 deliverables................................................................................................................................1.1.7 Contents of the report.......................................................................................................................................

2. RESULTS................................................................................................................................................................

2.1 LIST OF POTENTIAL ASAS APPLICATIONS..................................................................................................................2.2 GLOBAL DESCRIPTION OF THREE ASAS APPLICATIONS..............................................................................................2.3 GENERICITY OF THE ASAS APPLICATIONS.................................................................................................................2.4 DEFINITIONS............................................................................................................................................................

2.4.1 Traffic Situation Awareness applications..........................................................................................................2.4.2 Tactical Co-operative applications...................................................................................................................2.4.3 Strategic Co-operative applications..................................................................................................................

2.5 GLOBAL ASSESSMENT OF THE ADS-B TECHNIQUES FOR ASAS APPLICATIONS............................................................2.5.1 ADS-B communication media key points...........................................................................................................2.5.2 Conclusions......................................................................................................................................................

2.6 RTD ISSUES VERSUS RTD DOMAINS........................................................................................................................2.6.1 Operational concepts........................................................................................................................................2.6.2 Benefits & Constraints......................................................................................................................................2.6.3 Safety assessment..............................................................................................................................................2.6.4 ASAS operations and Human Factors...............................................................................................................2.6.5 ASAS design and Airborne functions including HMI.........................................................................................

2.6.5.1 ASAS design................................................................................................................................................................2.6.5.2 ADS-B media...............................................................................................................................................................2.6.5.3 ASAS functions...........................................................................................................................................................

2.6.6 Transition issues...............................................................................................................................................2.7 RTD PLAN...............................................................................................................................................................

2.7.1 RTD Plan Framework.......................................................................................................................................2.7.2 User Requirement or Concept Phase.................................................................................................................2.7.3 User Requirement Analysis or Feasibility Phase...............................................................................................2.7.4 Functional Requirement or Acceptability Phase...............................................................................................2.7.5 ASAS Development or Prototyping Phase.........................................................................................................2.7.6 Experimentation and Validation Phase.............................................................................................................2.7.7 Implementation Phase.......................................................................................................................................2.7.8 RTD Plan schedule...........................................................................................................................................2.7.9 Other remarks on the RTD plan........................................................................................................................

3. DISCUSSION..........................................................................................................................................................

3.1 THE APPROACH TO WP5...........................................................................................................................................3.2 MANAGEMENT OF THE TASKS...................................................................................................................................

3.2.1 WP5.1...............................................................................................................................................................3.2.2 WP5.2...............................................................................................................................................................3.2.3 WP5.3...............................................................................................................................................................3.2.4 WP5.4...............................................................................................................................................................3.2.5 WP5.5...............................................................................................................................................................

3.3 DISCUSSION OF THE RESULTS....................................................................................................................................3.3.1 Genericity of the ASAS application...................................................................................................................3.3.2 Global assessment of the ADS-B techniques for ASAS applications...................................................................

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3.3.3 RTD Plan.........................................................................................................................................................

4. CONCLUSIONS......................................................................................................................................................

5. RECOMMENDATIONS.........................................................................................................................................

6. APPENDIX A - LONGITUDINAL STATION KEEPING....................................................................................

6.1 DEFINITION..............................................................................................................................................................6.1.1 Operational purpose of the application.............................................................................................................6.1.2 Type of airspace...............................................................................................................................................6.1.3 Applicability to IFR and VFR...........................................................................................................................6.1.4 Required aircraft separation minima................................................................................................................

6.2 BENEFITS AND CONSTRAINTS....................................................................................................................................6.2.1 Benefits anticipated from the application..........................................................................................................

6.2.1.1 Common......................................................................................................................................................................6.2.1.2 ATC.............................................................................................................................................................................6.2.1.3 Pilot.............................................................................................................................................................................6.2.1.4 Airline.........................................................................................................................................................................6.2.1.5 ATS providers..............................................................................................................................................................

6.2.2 Constraints and limitations...............................................................................................................................6.2.2.1 Common......................................................................................................................................................................6.2.2.2 ATC.............................................................................................................................................................................6.2.2.3 Pilot.............................................................................................................................................................................6.2.2.4 Airline.........................................................................................................................................................................6.2.2.5 ATS provider...............................................................................................................................................................

6.3 SAFETY ASSESSMENT...............................................................................................................................................6.3.1 Integrity assessment..........................................................................................................................................6.3.2 Global collision risk assessment........................................................................................................................

6.4 DATA REQUIREMENTS..............................................................................................................................................6.4.1 Joining or establishing the stream:...................................................................................................................6.4.2 Maintaining the separation...............................................................................................................................6.4.3 Leaving or disestablishing the stream...............................................................................................................6.4.4 Handing over a stream to an other sector.........................................................................................................

6.4.4.1 Ground-ground data exchange:.....................................................................................................................................6.4.4.2 Air-ground data exchange:...........................................................................................................................................

6.4.5 Emergency procedures......................................................................................................................................6.5 DATA LINK REQUIREMENTS.....................................................................................................................................

6.5.1 Risk allocation..................................................................................................................................................6.5.2 Impact of position and velocity measurement error on warning time.................................................................6.5.3 Summary of datalink requirements for LSK.......................................................................................................6.5.4 Safety analysis consequences on the datalink requirements...............................................................................

6.6 PILOT INTERFACE REQUIREMENTS............................................................................................................................6.6.1 Human factors aspects......................................................................................................................................6.6.2 Display requirements........................................................................................................................................6.6.3 Aural indications..............................................................................................................................................6.6.4 Failure and mode selection indicators..............................................................................................................

6.7 ATC INTERFACE REQUIREMENTS..............................................................................................................................6.8 OPERATIONAL PROCEDURES.....................................................................................................................................

6.8.1 Actions and responsibilities taken by the pilot and the controller......................................................................6.8.2 Proposed actual separation between aircraft to be applied by the pilot during the procedure...........................6.8.3 Proposed new, or new usage of current, radiotelephony (R/T) phraseology.......................................................6.8.4 Limiting factors which could affect the application of the procedure.................................................................6.8.5 Controller’s responsibility to maintain a monitoring function;..........................................................................6.8.6 Proposed contingency procedures.....................................................................................................................

6.9 QUESTIONS TO ANSWER...........................................................................................................................................

7. APPENDIX B - CLOSELY SPACED PARALLEL APPROACHES IN IMC......................................................

7.1 DEFINITION..............................................................................................................................................................7.1.1 Operational purpose of the application.............................................................................................................7.1.2 Type of airspace...............................................................................................................................................7.1.3 Applicability to IFR and VFR...........................................................................................................................

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7.1.4 Required aircraft separation minima................................................................................................................7.2 BENEFITS AND CONSTRAINTS....................................................................................................................................

7.2.1 Benefits............................................................................................................................................................7.2.1.1 ATC.............................................................................................................................................................................7.2.1.2 Pilot.............................................................................................................................................................................7.2.1.3 Airlines........................................................................................................................................................................

7.2.2 Constraints.......................................................................................................................................................7.2.2.1 ATC.............................................................................................................................................................................7.2.2.2 Pilot.............................................................................................................................................................................7.2.2.3 Airlines........................................................................................................................................................................

7.3 SAFETY ASSESSMENT...............................................................................................................................................7.3.1 Integrity Assessment.........................................................................................................................................7.3.2 Global collision risk assessment........................................................................................................................

7.4 DATA REQUIREMENTS..............................................................................................................................................7.4.1 Update period and time stamping.....................................................................................................................7.4.2 Design constraints............................................................................................................................................

7.5 DATA LINK REQUIREMENTS.....................................................................................................................................7.5.1 Risk allocation..................................................................................................................................................7.5.2 Impact of position and velocity measurement error on warning time.................................................................7.5.3 Summary of datalink requirements for CSPA....................................................................................................7.5.4 This information on datalink requirement are requiring additional specific assessment and should not be limited to currently available literature.....................................................................................................................7.5.5 Safety analysis consequences on the datalink requirements...............................................................................


7.7 ATC INTERFACE REQUIREMENTS..............................................................................................................................7.7.1 Current requirements........................................................................................................................................

7.7.1.1 Independent parallel approaches...................................................................................................................................7.7.1.2 Dependent parallel approaches.....................................................................................................................................

7.7.2 CSPA requirements...........................................................................................................................................7.8 OPERATIONAL PROCEDURES.....................................................................................................................................

7.8.1 Actions and responsibilities taken by the pilot and the controller......................................................................7.8.1.1 Current ATC procedure................................................................................................................................................7.8.1.2 Planned CSPA procedure.............................................................................................................................................

7.8.2 Proposed separation between aircraft to be applied by the pilot during the procedure......................................7.8.3 Proposed new, or new usage of current, radiotelephony phraseology................................................................7.8.4 Limiting factors which could affect the application of the procedure.................................................................7.8.5 Controller’s responsibility to maintain a monitoring function...........................................................................7.8.6 Proposed contingency procedures.....................................................................................................................7.8.7 Example...........................................................................................................................................................

7.9 QUESTIONS TO ANSWER............................................................................................................................................

8. APPENDIX C : AUTONOMOUS AIRCRAFT......................................................................................................

8.1 DEFINITION..............................................................................................................................................................8.1.1 Operational purpose of the application.............................................................................................................8.1.2 Type of airspace...............................................................................................................................................8.1.3 Applicability to IFR and VFR...........................................................................................................................8.1.4 Required aircraft separation minima................................................................................................................

8.2 BENEFITS AND CONSTRAINTS....................................................................................................................................8.2.1 Benefits anticipated from the application..........................................................................................................

8.2.1.1 ATC.............................................................................................................................................................................8.2.1.2 Airline.........................................................................................................................................................................

8.2.2 Constraints and limitations...............................................................................................................................8.2.2.1 Common......................................................................................................................................................................8.2.2.2 ATS providers..............................................................................................................................................................8.2.2.3 ATC.............................................................................................................................................................................8.2.2.4 Pilot.............................................................................................................................................................................8.2.2.5 Airline.........................................................................................................................................................................

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8.3 SAFETY ASSESSMENT...............................................................................................................................................8.3.1 Integrity assessment..........................................................................................................................................8.3.2 Global collision risk assessment........................................................................................................................

8.4 DATA REQUIREMENTS..............................................................................................................................................8.4.1 Approaching free-flight area.............................................................................................................................8.4.2 Autonomous Aircraft operation:........................................................................................................................

8.4.2.1 Long term operations :.................................................................................................................................................8.4.2.2 Short term operation :..................................................................................................................................................

8.5 DATA LINK REQUIREMENTS.....................................................................................................................................8.5.1 Risk allocation..................................................................................................................................................8.5.2 Impact of position and velocity measurement error on warning time.................................................................8.5.3 Summary of datalink requirements for Autonomous Aircraft.............................................................................8.5.4 Safety analysis consequences on the datalink requirements...............................................................................


8.7 ATC INTERFACE REQUIREMENTS..............................................................................................................................8.7.1 Separation and conflict monitoring (where available).......................................................................................8.7.2 Aircraft intentions.............................................................................................................................................8.7.3 Number of aircraft in area................................................................................................................................

8.8 OPERATIONAL PROCEDURES...........................................................................................................................8.8.1 Actions and responsibilities taken by the pilot and the controller......................................................................8.8.2 Proposed separation between aircraft to be applied by the pilot during the procedure......................................8.8.3 Proposed new, or new usage of current, radiotelephony phraseology;..............................................................8.8.4 Limiting factors which could affect the application of the procedure;...............................................................8.8.5 Controller’s responsibility to maintain a monitoring function;..........................................................................8.8.6 Proposed contingency procedures.....................................................................................................................

9. ACKNOWLEDGEMENTS.....................................................................................................................................

10. REFERENCES......................................................................................................................................................

11. LIST OF SYMBOLS.............................................................................................................................................

12. LIST OF ABBREVIATIONS................................................................................................................................

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1Introduction

The information below can be found in more details in the WP5 Project Plan [1] (internal deliverable).

1.1.1WP5 ObjectivesThe first objective of WP5 is to perform an initial but domain-comprehensive assessment of the ADS-B techniques, characterised in WP3. Assessment will be made of their technical and operational capabilities to support flight-operation of aircraft enhanced situational awareness and Airborne Separation Assurance Systems (ASAS) within the (future) EATMS environment, wherever it is both feasible safety-wise and beneficial from an airspace capacity point of view.

The second objective is to take stock of the expected results achieved at the end of EMERALD and to produce recommendations for future RTD activities, documented as draft RTD plans for the consideration of decision makers both at European level (The EC and Eurocontrol) and national level (i.e. the CAA authorities, the EMERALD partners).

1.1.2Involved partnersTwo industry partners and three research centers are involved in the WP5. They are :

- SEXTANT AVIONIQUE- THOMSON-CSF- DERA- NATS- and CENA under the aegis of SOFREAVIASOFREAVIA is the lead partner for all WP5 tasks.

1.1.3WP5 tasksFive tasks have been identified in WP5:

- WP5.1 defines a WP5 project plan. and selects scenarios of interest for ADS-B/ASAS applications, taking into consideration different phases of flight and the different types of European airspace.

- WP5.2 assesses:- the technical performance of ADS-B techniques, in the context of the WP5.1

application scenarios;- ADS-B interaction with, and requirements for Cockpit Situational Awareness

avionics and display;- aircrew human factors issues, interaction with ground ATCOs;- transition from present ATM systems and operating procedures.

- WP5.3 consists in a wide-reaching consultation of a leading aircraft manufacturer, potential airline users, various task forces or working groups of interested

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organisations to discuss WP5.2 scenarios and gather ideas. It also seeks to achieve a unified view on the ADS-B supported operational scenarios and their assessment criteria via inter-project co-ordination with other EC projects. The main feature of WP5.3 is a one-day meeting with all the people described before but earlier contacts with them have been necessary to ensure a fruitful brainstorming.

- WP5.4 analyses results from WP5.3 and produces a global assessment of the adequation of ADS-B techniques for use in ASAS applications. Furthermore, a RTD plan on the issues identified in WP5 is designed.

- WP5.5 consolidates the work done in WP4 taking into account comments from the users’ community, prepare the WP5 technical report and gives an oral presentation during EMERALD seminar.

1.1.4WP5 effort and scheduleEffort was planned for each task as follows (in man days of effort):

WP5 Tasks Total (m-days)

5.1 Potential ASAS applications 51

5.2 Feasibility assessment 159

5.3 User’s interview 23

5.4 Assessment report, RTD Plan 76

5.5 User’s feedback 35

Total (m-days) 344

The involvement of the partners was initially planned as follows :

Partner SOF DERA NATS SXT THO Total (m-days)

Total (m-days) 138 50 4 66 86 344

The total planned effort for WP5 was 17 man months, beginning 1st July 1997 and finishing 8 months later. In fact, for the benefit of the project the partners contributed additional effort in excess of 50-100% of the estimate. In particular, NATS decided to contribute extra effort to benefit from the work.

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The schedule of the tasks and the various meetings was as follows:

NomWP 5.1 : Identification of ADS-B/ASAS applicationsWP 5.2 : Feasibility assessmentWP 5.3 : Users' interviewWP 5.4 : Assessment report and RTD planWP 5.5 : Users' feedbackWP5-KOMWP5-PM1WP5-PM2Users' interviewWP5-PM3EMERALD Seminar

Jul Aoû Sep Oct Nov Déc Jan Fév Mar Avr

WP5-KOM (Kick-Off Meeting) and WP5-PM# (Progress Meeting) are internal meetings to review the previous work and coordinate the next work.

Despite a very tight schedule, the work was completed on time.

1.1.5Internal WP5 deliverablesFrom WP5.1:

- EMERALD/WP5/SOF/001 - WP5 Project Plan- EMERALD/WP5/SOF/007- ADS-B/ASAS applications review and selection

From WP5.2:

- EMERALD/WP5/SOF/009 - Detailed feasibility assessment of selected ADS-B/ASAS applications

From WP5.3:

- Presentation aids made for the user’s meeting by the partners- EMERALD/WP5/SOF/010 - Detailed feasibility assessment of selected

ADS-B/ASAS applicationsFrom WP5.4:

- EMERALD/WP5/SOF/012 - Global assessment of ADS-B techniques for their use in ASAS applications and RTD plan for further studies in the domain

From WP5.5:

- EMERALD/WP5/SOF/014 - Research and Technical Development (RTD) Plan for ASAS Concept Development

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1.1.6External WP5 deliverablesThe external WP5 deliverables are in fact internal deliverables (ID) for the whole EMERALD project (see the document ‘Schedule for Project EMERALD’ - DERA/LS1(ATC)/EMERALD/PLANS/005/1.0):

- ID5-1 - Redline version of WP5 technical report to be delivered to DERA on 20 February 1998

- ID5-2 - Fully revised version of WP5 technical report and presentation aids for the EMERALD seminar to be delivered to DERA on 6 March 1998

1.1.7Contents of the reportThis document include the following items:

- a result section;- a discussion section;- a conclusion section;- a recommendation section;- and three appendices.

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2Results

2.1List of potential ASAS applicationsAfter investigating documents from various organisations (RTCA, EUROCAE, SICASP, EUROCONTROL) and projects (NEAN, NEAP, FREER), the partners gathered 32 ASAS potential applications, which are given in the following table. They are listed with the type of airspace in which they apply, their estimated timescale and the type of benefit they are supposed to bring.

N° Name Type of airspace Term Expected benefits

Oceanic, en route and

remote non-radar

En route

Terminal Airport Short Medium Long Safety Capacity Efficiency

1 ASAS CROSSING PROCEDURE X X X X X

2 ALERT OTHER AIRCRAFT, ATC AND FLIGHT SERVICE OF PILOTS WITH SPECIAL NEEDS

X X X X X X X

3 AUTOMATIC WEATHER REPORTING X X X X X X X X

4 AUTONOMOUS AIRCRAFT X X X X X

5 BAROMETRIC ALTITUDE AND GNSS HEIGHT REPORTING FOR RVSM CONFORMANCE MONITORING

X X X X X X

6 CLOSELY SPACED PARALLEL APPROACHES IN IMC

X X X X X

7 COLLABORATIVE RE-ROUTING X X X X X X X

8 COLLISION SITUATIONAL AWARENESS

X X X X X X X

9 CONFLICT MANAGEMENT WHILE PERFORMING SELF-SEPARATION FOR FREE FLIGHT

X X X X X X X X

10 CONFLICT SITUATIONAL AWARENESS

X X X X X X X

11 DEPARTURE SPACING X X X X

12 ENHANCED COCKPIT SITUATIONAL AWARENESS FOR CONVERGING RUNWAY APPROACHES AND/OR LAND-AND-HOLD-SHORT APPLICATIONS

X X X X X

13 ENHANCED IFR SURFACE OPERATIONS

X X X X X

14 ENHANCED VISUAL ACQUISITION OF OTHER TRAFFIC FOR « SEE AND AVOID »

X X X X X X X

15 ENHANCED VISUAL ACQUISITION OF OTHER TRAFFIC IN THE VFR TRAFFIC PATTERN AT UNCONTROLLED AIRPORTS

X X X X X

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N° Name Type of airspace Term Expected benefits

Oceanic, en route and

remote non-radar

En route

Terminal Airport Short Medium Long Safety Capacity Efficiency

16 ENHANCED VISUAL APPROACH X X X X X

17 ESTABLISH IN-TRAIL SPACING INTERVAL

X X X X

18 FINAL APPROACH SPACING X X X X

19 IN-TRAIL CLIMB, IN-TRAIL DESCENT X X X X X

20 LATERAL PASSING MANEUVERS X X X X X

21 LEAD AIRCRAFT GLIDEPATH VISUALISATION

X X X

22 LEAD CLIMB AND DESCENT X X X X

23 LOW ALTITUDE STATION KEEPING X X X X

24 NAVIGATION GUIDANCE FOR LOST OR DISORIENTED AIRCRAFT(2)

X X X

25 PASSING MANEUVERS X X X X

26 PATROL FLIGHT(1) X X X

27 RUNWAY AND FINAL APPROACH OCCUPANCY AWARENESS

X X X

28 RUNWAY INCURSION MONITORING WHILE CROSSING RUNWAYS AND TAXIWAYS(2)

X X X X X

29 STATION KEEPING X X X X

30 SURFACE SITUATIONAL AWARENESS

X X X X X

31 SURVEILLANCE ENHANCEMENTS FOR TCAS/ACAS

X X X X X X

32 TRAFFIC SITUATIONAL AWARENESS X X X X X X

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2.2Global description of three ASAS applicationsThis result details three selected applications :

- Longitudinal station keeping (LSK): this application should allow aircraft on one track to maintain longitudinal separation in an in-trail stream.

- Closely spaced parallel approaches (CSPA): this application should provide the safety required to conduct parallel approaches with lower minimum spacings between runways.

- Autonomous aircraft (AA): this application should allow aircraft to self de-conflict with other aircraft, without tactical ground control

For each application, according to the SICASP ASAS template, are investigated:

- the aim of the application;- the benefits and constraints;- the safety assessment;- the data and data link requirements;- the pilot interface and ATC interface requirements;- the operational procedure.

Those points are developed in WP5.3 and copies of the three descriptions are attached as Appendix A, B and C.

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2.3Genericity of the ASAS applications

2.4DefinitionsASAS applications may be classified into three different classes:

- Traffic Situation Awareness (TSA) applications;- Tactical Co-operative (TC) applications;- Strategic Co-operative (SC) applications.Our main assumption is that the requirements of each class include those of the previous class. This method gives three equipment classes, each being roughly more complex and potentially having a later applicability date than the previous.

2.4.1Traffic Situation Awareness applicationsThis is the first stage on the way to more complex ASAS applications. These applications will provide the pilot with data on his environment (traffic, airspace,...). A Cockpit Display of Traffic Information (CDTI) will be used for such applications.

An increase in traffic situation awareness may occur even when the percentage of ASAS equipped aircraft is small. The benefits to equipped aircraft increase as other aircraft equip, and full traffic situation awareness is achieved.

Other Traffic Situation Awareness applications could be envisaged (weather reporting, airport information,...) but are out of the scope of EMERALD.

No responsibility delegation is required for this class.

2.4.2Tactical Co-operative applicationsThese applications will help to manage the relative movement between two aircraft while they are in close proximity to each other.

They can be divided into two sub-classes:

- Distancing applications: in these applications the two aircraft are close to each other only for a very short duration.

- Shadowing applications: in these applications, the two aircraft are required to stay at the same distance for some time.

Moreover, the aircraft could be either automatically guided by the TC application or not. An example of the former is the ASAS Crossing Procedure (ACP), and an example of the latter is the Closely Spaced Parallel Approach (CSPA) application in IMC, both applications having been studied in WP5.2.

The pilot will receive full responsibility delegation from the controller for the duration of the application and for the specific purpose of separation with the aircraft involved in the application. This is because applications envisage that the pilot will use ASAS to maintain separation from specified aircraft and controllers cannot be responsible for the pilots actions, even though the controller might retain some responsibility for monitoring satisfactory maintenance of the required separation (personally or automatically).

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2.4.3Strategic Co-operative applicationsThese applications will help the pilot to manage his own route, in agreement with other aircraft and ATC, over a long time horizon. Unlike the TC applications, more than two aircraft can be involved simultaneously in SC applications. The Autonomous Aircraft (AA) application, studied in WP5.2, is one of them.

The aircraft will be guided automatically by the SC application, under the aegis of the pilot.

The pilot will receive full separation responsibility for the time he flies in the airspace reserved to the SC application. This would be the case for example in the FFAS definition in the EATMS Operational Concept Document [2], which covers only low density airspace. This application may support progress to Free Flight but cannot by itself enable Free Flight. ‘Co-operative ATC’ is still needed for this application.

It would at first appear that TSA is the least demanding class of application and SC the most demanding. However, some TC applications may be implemented in high density airspace leading to a longer pre-implementation phase than is currently envisaged for SC applications. Indeed, the high traffic density implies reduced aircraft manoeuvrability and increased pilot workload, and also may include the approach phase of flight. This may result in greater complexity of operation than for SC applications.

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2.5Global assessment of the ADS-B techniques for ASAS applications

2.5.1ADS-B communication media key pointsThe following table sums up the main features of the two prominent ADS-B techniques and gives the view of the WP5 on their applicability to ASAS for each point.

Mode S STDMA Conclusions

Media Access Asynchronous mode Conscious slot stealing (R. Hood)

Hidden transmitters

STDMA is expected to be more efficient, but Mode S is simpler

Dependency and spoofing

Loss of GPS receiver

· synchro from other stations

Loss of GPS system

· floating network

· # 15% loss throughput

Mode S can be used on its own and as backup for other systems.

STDMA is partly dependent on 3rd party space segment and subject to spoofing.

Capacity Airports: 150 stations, update period 1s: P = 85%

Terminal: 750 stations, update period 5s: P = 82%

En route: 1500 stations, update period 10s: P = 93%

Airports: 150 stations, update period 1s: P = 96%

Terminal: 750 stations, update period 5s: P = 96%

En route: 1500 stations, update period 10s: P = 89%

STDMA is expected to be more efficient than Mode S STDMA capacity is only dependent on the number of frequencies assigned to ADS-B

Range 50 to 100 NM up to 200 NM STDMA is expected to have better range performances

Spectrum and growth capability

One up-link and one down-link frequency, but has already global frequency acceptance.

Mode S has no availability for additional channels

Difficulty in obtaining global signalling channels world-wide.

STDMA may be allocated additional local channels to meet increases in traffic, but that would require methods to switch channels by region.

Mode S may be easier to implement in the short term but may be limited in the longer term

Implementation and transition

Technology is mature and natural transition from the current avionics but with limited capability

Standardisation still in progress, and antenna issues still to be solved

It will be easier to certify an ADS-B system based on Mode S in the short term and for limited use.

Cost effectiveness

Expected to be marginally more expensive than other alternative, but cost effective for air carriers already equipped with TCAS II (modification)

Perceived as cheaper than mode S solution for the airborne components, but remaining difficulties still to addressed.

To be further investigated in a global system approach including airborne and ground applications

2.5.2Conclusions- ASAS applications can be supported by both technologies which have different

levels of maturity and different performances but none of them is suitable for

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all applications. Furthermore, ADS-B may not be sufficient to support all applications, and may require a crosslink capable device.

- During the transition period, to address the partial equipage of the fleet, inducing a partial visibility of the surrounding traffic, the TIS (Traffic Information Service) or TIS-B (TIS-Broadcast) could be used.

- The common point of failure of ASAS applications is the aircraft navigation system. This implies that ASAS applications will require a position validation.

- For all ASAS applications except TSA applications, the integrity and availability requirements demand a redundancy, especially in the communication channel. A dual communication channel would be satisfying. Furthermore, such applications need intents in order to work efficiently and safely.

- The ASAS/ACAS compatibility should be carefully assessed in order to ensure proper acceptance by pilots.

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2.6RTD Issues versus RTD DomainsThis section collects the issues identified during WP5.4 and WP5.5. These issues are classified under the following high level domains:

- Operational Concepts;- Benefits & Constraints;- Safety Assessment;- ASAS Operations and Human Factors;- ASAS Design and Airborne functions including HMI;- Transition Issues.

The acronyms FFAS for ‘Free Flight Airspace’ and MAS for ‘Managed Airspace’ are often used in the following sections. The FFAS and MAS definitions come from the EATMS Operational Concept Document [2].

2.6.1Operational conceptsIt is necessary to identify and evaluate if there are any benefits with specific significance to European Airspace for implementing ASAS. In other words: does an operational requirement exist?

RTD issue A1: There is a need for a European operational concept on ‘Co-operative Air Traffic Control’, leading to a list of applications relevant for Europe, in the EATMS frame.

Given the differences in structure of the European and US airspace, and also the different concerns of airline operators, early ASAS applications are likely not to be the same in these two regions. The definitions of the generic ASAS applications are not in their definitive form yet.

RTD issue A2: An international consensus through ICAO standards is required to allow aircraft operators to obtain the expected benefits world-wide.

The new responsibilities of the air traffic actors mainly pilots and controllers but also aircraft operators and ATM providers must be clearly understood.

RTD issue A3: The definition of the new responsibilities due to the ‘Change of Role in ATC’ is a major issue.

Airspace design, airspace structure will have to be adapted to obtain full benefit from ASAS.

RTD issue A4: Analysis of implications of change in airspace structure on national boundaries/interests and airspace legislation/agreements need to be conducted, e.g. the issue of an ATS provider offering a differential service to aircraft with different levels of ASAS equipage.

Fast time simulations are also necessary to evaluate the limits on aircraft performance, which influence the development of the ASAS applications and supporting operational concepts. The ASAS applications cannot be fully developed until the implications of effect of aircraft performance is fully understood.

RTD issue A5: Studies are required to investigate how different aircraft performances may affect the development of the operational concept for a given ASAS application.

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2.6.2Benefits & ConstraintsIn order to validate the expected benefits, fast-time simulations should be conducted. If the simulations are conclusive, large-scale real time simulations and thereafter trials could be envisioned. This last point may also imply a new airspace design. The expected benefits are related to more flexibility for the users and increased capacity.

Fast time simulations are also necessary to estimate fuel benefits and reduction in delays.

RTD issue B1: Studies need to be conducted to evaluate the operational benefits and the constraints linked to ASAS implementation.

ASAS implementation will require financial investments on the airborne and the ground sides.

RTD issue B2: Cost/benefit analysis will be a driver for ASAS implementation.

One of the difficulties linked to the above issues is to take into account mixed-equipage scenarios where not all the aircraft are suitably fitted with ASAS equipment. From the perspective of identifying benefits, it will be important to identify and provide benefits to the first fleets to equip, to encourage early equipage.

RTD issue B3: The identification of the benefits of early ASAS equipage.

2.6.3Safety assessmentThe ASAS applications will be accepted if they maintain at least the current safety level.

Generally the entire hypothesis taken in the EMERALD safety assessment have to be reconsidered and improved.

The Raw Collision Risk model per ASAS application has to be more complete and accurate to allow a pertinent safety assessment of the ASAS operations. It could take into account for each ASAS procedure the concepts of risk of separation loss and risk of collision after separation loss.

A full risk assessment process has to be performed following recognised methodologies.

This will provide failure conditions, safety objectives, safety-related procedures and safety requirements.

This process calls for many tools, techniques and methods. The analyst will select the most appropriate for each risk assessment, driven by the process.

Risk assessment needs to include assessments for the aircraft segment and for the ground ATC segment. In order to confirm that safety requirements are passed between segments and that these segments incorporate such requirements, it is necessary to ensure that co-ordination between segments occur. Co-ordination between all the actors of the implementation of the ADS-B / ASAS is one of the major issues of the data-link safety process. The safety assessment process will have to be conducted separately (but in a co-ordinated manner) in the aircraft segment and in the ground ATC segment.

Once safety requirements and objectives have been agreed and standardised, it is up to any organisation in the aircraft and ground ATC domains to define the architecture of its system and to show the compliance of its system with the requirements.

It would also take into account a model of the ultimate safety net represented by the pilot. How pilots manage ASAS failures requires further considerations.

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The Global Collision Risk model has to be completed to take into account the potential limits of the ASAS algorithms for conflict detection and resolution. The safety model of the aircraft environment (like ATC surveillance) has to be improved.

The availability and integrity of future navigation means have to be assessed carefully.

The impact of a “party line” and the data-link should be assessed.

The target level of safety has to take care of the different types of aircraft and airspace.

RTD issue C1: A full system safety study should be conducted to validate the figures given in the preliminary study and to assess the real impact of the ASAS system on the aircraft systems as a whole, including human factors.

It is assumed that ASAS applications will be supported by ATC and ground systems. This may mean that a ‘conformance monitor’ is required by ATC to assist ATC in emergencies, as ATC may not have the same ‘air picture’ that they currently have. This type of safety net may also be required in the cockpit.

RTD issue C2: Investigate requirements for a ground based conformance monitor.

RTD issue C3: Safety methodology has to be defined for the specific case of ASAS / ADS-B concept. For that purpose, various environment will have to be defined (operational requirements, safety requirements (for ATC and aircraft systems), failure conditions...).

RTD issue C4: Preliminary System Safety Assessments (PSSA) is a systematic examination of candidate system architectures to determine how safety objectives and requirements can be met and how the failures of the designed system can contribute to the functional failure condition identified by Functional Hazard Assessments (FHA). It has to be performed at the early stage of the system design and will be driven by the iterative steps of the design process: functions are allocated to system elements and safety objectives and requirements are apportioned accordingly.

RTD issue C5: Two FHAs have to be conducted, one for the airborne segment and one for the ATC segment.

RTD issue C6: System Safety Assessment (SSA) is the continuation of PSSA and demonstrates that the system and their elements, meet the safety objectives and requirements.

2.6.4ASAS operations and Human FactorsRTD issue D1: The airspace organisation (i.e. route structure and « free route » structure) where ASAS applications will be implemented need to be defined.

RTD issue D2: In the case of FFAS, the role of the ground system need to be defined and is essential. A distinction should be made when FFAS in implemented over remote area (oceanic or desert areas) or when the ground ATC system can provide back-up through for example ground surveillance. In FFAS, the ground could be responsible to provide meteorological data, information on expected traffic density, traffic information on aircraft, which are not suitably equipped and other services. Where ground surveillance exists, aircraft position data transmitted via the ADS-B medium could be validated.

RTD issue D3: The transition between FFAS and MAS is essential and may require the definition of transition zones where aircraft could be provided with special ATM services for example to enter the MAS in time.

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RTD issue D4: In MAS, to obtain maximum benefit from ASAS procedures, the controller should be provided with tools to identify situations where separation transfer can take place. Monitoring tools may also be required to maintain the controller’s traffic situation awareness and his ability to cope with non-standard situations.

RTD issue D5: ASAS procedures should clearly implement the share of responsibility defined in the operational concept.

RTD issue D6: The FFAS will require the implementation of Extended « rules of the air ». Compatibility with the existing rules of the air will be required if the airspace is not segregated to suitably equipped aircraft.

RTD issue D7: Depending on ASAS applications and procedures, airborne separation minima need to be defined.

RTD issue D8: For each ASAS application, contingency procedures need to be defined. They shall not be based on the fact that aircraft are fitted with ACAS.

RTD issue D9: ASAS procedures shall be compatible with ACAS procedures.

RTD issue D10 : The controller and pilot workloads need to be assessed. Depending on the phase of flight, the ASAS application and the traffic density, the workload might be reduced or increased (and may be incompatible with the current workload).

RTD issue D11: Pilots and controllers’ training is essential and shall be in line with the operational ASAS procedures. The implementation of a CDTI, which can be seen as a necessary component of an ASAS and the simplest ASAS application, will require operational procedures and pilot’s training to avoid wrong uses of the system.

2.6.5ASAS design and Airborne functions including HMI

2.6.5.1ASAS designRTD issue E1: Study of airborne architecture for integration of ASAS functions and impact on navigation data source, FMS, CDTI, etc.

RTD issue E2: Algorithms for conflict detection, conflict resolution, separation assurance manoeuvres shall be studied. Compatible resolutions between aircraft are required. Dedicated algorithms might be necessary for ASAS applications linked to traffic flow management (merging of traffic, longitudinal station keeping, parallel routes, etc.).

Different definitions of ‘intent’ data exist in the many standards organisations. In addition the existence of a standard does not necessarily guarantee that the data is available from common or future FMSs or data buses.

RTD issue E3: There may be a requirement for exchange of intent (flight plan, trajectory change points, etc.) and ASAS capabilities between aircraft and to the ground depending on the ASAS applications. It is therefore necessary to define the requirement, identify if the data is available and convey the information to the users.

RTD issue E4: Depending on the criticality of the ASAS application, monitoring functions will have to be studied and may involve dual channel architecture and hot back-up.

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RTD issue E5: ASAS and ACAS might share some components but the loss of the ASAS functions shall not be detrimental to the ACAS function. The ACAS shall remain the last ditch in case of navigation failure and separation assurance failure.

RTD issue E6: ATC may have to provide aircraft with specific services, TIS, position validation. The design of ground ATC stations has to be further investigated.

2.6.5.2ADS-B mediaASAS applications will use extensively data convey through ADS-B media. The requirement on the ADS-B media for ASAS will be application dependent and none of the addressed media (STDMA or Mode S) seems to fulfil all the requirements. The following issues are critical for ASAS implementation :

a - General issues related to STDMA and Mode S

RTD issue E7: The quality of ADS-B data (e.g. position, velocity, etc.) shall be evaluated. The availability and integrity of future navigation means have to be assessed carefully. Furthermore, there is an issue when merging data coming from different sources.

RTD issue E8: The update rate and the surveillance range shall be validated. The actual performances shall be known and measured with various types of aircraft.

RTD issue E9: The ADS-B medium shall provide the means to co-ordinate separation assurance manoeuvres between aircraft. The protocol to be used shall be very reliable.

RTD issue E10: The capacity versus the performance of the media needs to be analysed.

RTD issue E11: Protection of spectrum and frequencies against spoofing has to be investigated.

b - Issues related to STDMA

RTD issue E12: The garbling of position data needs to be investigated if two aircraft, not within the STDMA range of each other, use the same slot to broadcast their position.

RTD issue E13: Report rate might be insufficient during the en-route phase (10 seconds) to perform some ASAS applications

RTD issue E14: Dependency on GPS for time synchronisation might be a constraint.

RTD issue E15: STDMA equipment should be compatible with VHF Data Radio (VDR) standards.

RTD issue E16: The onboard installation of SDTMA raises several issues especially, the number of required antenna and the potential use of splitters or combiners.

c - Issues related to Mode S

RTD issue E17: The current onboard architecture of Mode S needs to be revisited if for example a hot back-up is required.

With Mode S, there may be some common elements to the ASAS and ACAS equipment on the aircraft. This could include a common Mode S transponder and antennae, common ADS-B information, and even a common display. The issue of the common point of failure of one or more of these elements may need to be considered.

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RTD issue E18: Investigate how to protect the integrity of the collision avoidance function, whilst sharing common elements between ACAS and ASAS to avoid common point of failure.

RTD issue E19: Dual ASAS architecture may require a prohibitive number of antennae or the use of shared antennae.

2.6.5.3ASAS functionsWhen designing a CDTI for ASAS applications the issue of pilot workload will need to be considered. However, pilots are already using their TCAS displays to provide them with traffic situation awareness. There may already be some expectation that further traffic situation awareness will be achieved by combining the TCAS display with an ASAS display. The safety of one or more elements of collision avoidance and separation assurance functionality must be carefully considered.

RTD issue E20: Investigate whether TCAS and ASAS display presentations could be safely combined on a common CDTI.

There are no technological limitations (computation power, memory size, data-flow size, screen size, screen resolution, etc.) for the implementation of ASAS related symbologies.

RTD issue E21: The integration of ASAS in the current cockpits is an issue. The on-board architecture may have to be adapted for example to support automatic functions (e.g. station keeping control and monitoring functions).

RTD issue E22: Experimentation and operational validation of ASAS HMI are required.

RTD issue E23: ASAS HMI should also take into account the introduction of new technologies (head-up display, speech recognition, etc. ).

2.6.6Transition issuesDuring the transition phase -when there is a mixed population of non-equipped and ADS-B equipped aircraft - it will be necessary to consider which ASAS applications are feasible to implement.

RTD issue F1: To determine which ASAS applications would be feasible during a transition phase.

Those ASAS applications which only require pairs of aircraft to be ASAS/ADS-B equipped may not be required to operate in FFAS, and may operate in MAS in the vicinity of non-equipped aircraft following current ATC procedures.

RTD issue F2: To determine the feasibility of ASAS applications in MAS.

Some ASAS applications may require that an aircraft is aware of all other aircraft in its vicinity, even those not involved in the ASAS application.

RTD issue F3: To determine how to provide ADS-B/ASAS information to equipped aircraft about non-equipped aircraft. Implementation of new ground functions like TIS or TIS-B is a possible solution.

In order to support a transition phase to full ADS-B/ASAS equipage it will be important to encourage early equipage, and be able to demonstrate the benefits of early equipage to all airspace users.

RTD Issue F4: Demonstrate the benefits of early equipage.

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2.7RTD PlanThis section introduces the RTD plan proposed to address the identified issues.

2.7.1RTD Plan FrameworkThe framework of the RTD Plan is based on:

- user requirements: the aircraft operators, pilots, controllers, aircraft manufacturers and ATM service providers will have to be continuously involved;

- a more co-operative ATM process (with transfer of the responsibility in the cockpit and improvement of the traffic situation awareness) is seen as one mean for enabling the increase of the airspace capacity;

- safety requirements: the safety level will have to be increased or at least maintained;

- a cost-benefit approach for decision-making;- an applicative approach, i.e., the development of specific ASAS services for

addressing the transition from the current system to the future ATM.The RTD Plan follows a model usually applied to the development of complex systems, going from the user requirements to the validation by users but with a recursive approach:

- User Requirement or Concept Phase- User Requirement Analysis or Feasibility Phase- Functional Requirement or Acceptability Phase- ASAS Development or Prototyping Phase- Experimentation and Validation Phase- Implementation Phase

The implementation phase is not part of the RTD plan but it is mentioned to highlight what is really necessary to achieve before starting implementation.

In the following sections, each phase will be presented with a general description followed by a matrix detailing the tasks to be accomplished. For each task, references to the relevant issues are given.

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2.7.2User Requirement or Concept PhaseA lot of work has already been done on future concepts and it is not necessary to develop again new concepts.

On the basis of the EATMS Operational Concept Document, the concept of ‘Co-operative Air Traffic Control’ needs to be investigated into more details.

Operational requirements for ASAS applications need to be elaborated taking into account the potential benefits and constraints.

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Operational Concepts

Benefits & Constraints

Safety Assessment ASAS Operations and Human Factors

ASAS Design and Airborne HMI

Transition Issues

User Requirement or Concept Phase

- Define an operational concept on ‘Co-operative ATC’ for Europe (A1)

- Investigate how aircraft performance affects the concept (A5)

- Identify potential benefits & constraints (B1)

- Identify the benefits of early ASAS equipage (B3)

- Assess the suitability of the EATMS airspace structure for ASAS operations (D1)

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2.7.3User Requirement Analysis or Feasibility PhaseA lot of work is needed to successfully pass this phase.

It is necessary to select the ASAS applications which are the more relevant to cover European needs. This selection should be made after evaluating the benefits (capacity, flexibility, safety) and the constraints (pilot and controller workloads).

If aircraft autonomous mode of operation is envisaged in the FFAS, the role of the ground system needs to be defined. The transition between FFAS and MAS requires investigation.

An initial cost/benefit analysis has to be conducted. Aircraft operators will have to invest in new airborne equipment, maintenance and training. The analysis should include the cost of the ATM services.

On the basis of the selected ASAS applications, operational scenarios need to be defined. These scenarios should show the feasibility of ASAS applications and will also serve for the following phases of the RTD plan. The scenarios should take into account the transition issues.

It is necessary to define the new share of responsibility between the pilots and the controllers to implement Co-operative ATC. For the FFAS, the aircraft operators, the ATS providers and the States will play a different role than in the current ATM environment. Been autonomous means more responsibility for the aircraft operators. To ‘avoid the jungle’ and maintain the level of safety, States will have to implement at least new monitoring functions.

Technical issues need also to be addressed. Some issues are related to the ADS-B media (Mode S and STDMA). At the end of this phase, ADS-B data requirements for ASAS applications should be available.

It should be noted that only two ADS-B media were investigated during the EMERALD WP5 work. At that time, these two media have proved through trials their technical reality. For the future, potential candidates are also UAT (Universal Access Transceiver) and RA DLS (Range Applications Data Link Subsystem).

Several tasks on the Airborne Separation Assurance System are also essential. They range from ‘define an airborne architecture’ to ‘study a suitable HMI’. It is essential not to forget in between ‘study ASAS algorithms’, ‘define the aircraft intent’, ‘study the compatibility with ACAS’, etc.

The idea of defining a new ‘change in role’ is fine but the level of safety needs to be, not maintained but, increased to satisfy the European strategy objectives. Studies need to be conducted to see if the safety objectives can be achieved when implementing new operational procedures and new technologies.

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ASAS Design and Airborne functions

Transition Issues

User Requirement Analysis or Feasibility Phase

- Define and select ASAS applications for Europe (A1)

- Establish the new share of responsibility between pilots & controllers (A3)

- Study the impact on the airspace boundaries and organisation (A4)

- Develop an international (ICAO) consensus on ‘Co-operative ATC’ (A2)

- Investigate how aircraft performance affects the feasibility of ASAS applications (A5)

- Evaluate potential benefits (capacity and flexibility) & constraints through fast-time simulations in various airspaces (B1)

- Conduct an initial cost/benefit analysis (B2)

- Conduct an initial safety study (C1)

- Investigate requirements for a ground based conformance monitor (C2)

- Review of candidate system architectures to determine how safety objectives and requirements can be met. Functions are allocated to system elements and safety objectives and requirements are apportioned accordingly (C4)

- Define the airspace structure for ASAS operations (D1)

- Define the role of the ground system in FFAS and the associated ATM functions (D2)

- Study the transition between FFAS and MAS (D3)

- Define the user requirements for the necessary tools for the ground system for ASAS operations in MAS (D4)

- Identify the limitations on ASAS linked to ACAS operations (D9)

- Define operational scenarios for the selected ASAS applications (A1)

- Conduct a study on the airborne architecture for the integration of ASAS functions (E1 & E6)- Study ASAS algorithms (E2)- Identify the limitations on ASAS linked to ACAS algorithms (E5)- Define the various options for the aircraft intent (E3)- Study ASAS monitoring and back-up to achieve required criticality performance (E4)- Study and address the STDMA issues (E12 to E15)- Study and address the Mode S issues (E17 to E19)- Define the ASAS requirements for the ADS-B media (E7 to E11)- Define the user requirements for ASAS HMI (E20 to E23)

- Determine the feasibility of ASAS applications during the transition phase (partial ASAS equipage) (F1 & F2)

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Assessment of emerging technologies: the specific case of ADS-B/ASAS12 March 1998

EMERALD/WP5/SOF/015/1.0Version 1.0

2.7.4Functional Requirement or Acceptability PhaseThe hypothesis is that operational requirements, operational scenarios and requirements for the ADS-B data are available.

This phase will consist in elaborating the functional requirements and selecting the technical options on the basis of several studies and simulations.

The tasks are defined in the next table and they are all very important. The following four tasks are seen as essential:

- Define operational procedures for the selected ASAS applications addressing the new share of responsibility;

- Define the ‘New Rules of the Air’ and the airborne separation minima. The establishment of separation minima to be applied by ground ATC is a difficult task and a specific panel within ICAO (RGCSP - Review of the General Concept of Separation Panel) is in charge of it. Defining ‘airborne separation’ minima is a real new challenge;

- Conduct a cost/benefit analysis. It seems that if the cost/benefit analysis is not conclusively positive at this stage, it is not necessary to pass to the next phase of the RTD plan;

- Address the transition issues : impact upon aircraft operators and ATM organisations, suitable rate of ASAS equipage for ASAS operation acceptability.

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Transition Issues

Functional Requirement or Acceptability Phase

- Define Operational procedures for the selected ASAS applications (A1)

- Identify if the operational procedures reflect correctly the new share of responsibility (A3)

- Draft ICAO operational standards for the selected ASAS applications (A2)

- Identify the necessary changes on the airspace boundaries and organisation (A4)

- Evaluate potential benefits & constraints through fast-time simulations (B1)

- Conduct a more comprehensive cost/benefit analysis (B2)

- Conduct a more comprehensive safety study (C1)

- Two FHAs have to be conducted, one for the airborne segment and one for the ATC segments (C5)

- Define the ASAS procedures and contingency procedures (D5 & D8)

- Define the ‘New ‘Rules of the Air’ and the airborne separation minima (D6 & D7))

- Evaluate controller & pilot workloads on a theoretical basis (D10)

- Study compatibility between ASAS and ACAS procedures (D9)

- Refine the operational scenarios for the selected ASAS applications with the knowledge of the ASAS procedures (A1)

- Define the functional requirements for the tools necessary for the ground system for ASAS operations (D2 & D4)

- Define an airborne architecture for the integration of ASAS which achieves the required criticality performance and maintains the independence of ACAS (E1, E4, E5 & E6)

- Select ASAS algorithms after validation through off-line simulations (E2)

- Evaluate the compatibility between ASAS and ACAS algorithms through off-line simulations (E5)

- Select an option for the aircraft intent (E3)

- Draft ICAO technical standards for ASAS (E2 & E3)

- Select an ADS-B media architecture (E7 to E19)

- Define the functional requirements for an ASAS HMI (E20 to E23)

- Estimate the suitable rate of ASAS equipage for ASAS operation acceptability (F1)

- Determine the acceptability of ASAS applications during the transition phase in MAS (F2)

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2.7.5ASAS Development or Prototyping PhaseWhen functional requirements are available (preceding phase), it is possible to start development of prototypes. It should be noted that these developments are not limited to the airborne side but also include the ground systems.

Off-line simulations will need to be conducted to evaluate ASAS algorithms and compatibility with ACAS.

After some iterations, it should be possible to develop draft industry standards for ASAS.

At this stage, it will be also necessary to address initial training programmes for pilots and controllers. It is essential to prepare pilots and controllers to this new ‘change of role’.

At the end of this phase, real-time ASAS mock-ups should be available for demonstration to pilots and controllers.

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Transition Issues

ASAS Development or Prototyping Phase

- Evaluate the impact of the system architecture on safety (C1)

- FHAs are based on a top-down iterative approach in order to analyse system functions with more and more details, the consequences of their failures and the potential mitigating means (C4)

- Develop initial controller and pilot training programmes (D11)

- Develop the tools necessary for the ground system for ASAS operations (D2 & D4)

- Design an ASAS equipment or a suitable airborne architecture for the integration of ASAS which maintains ACAS independence (E1, E4, E5 & E6)

- Develop an ASAS prototype and implement ASAS algorithms (E1 & E2)

- Implement the selected ADS-B media architecture (E7 to E19)

- Design and implement an ASAS HMI (E20 to E23)

- Draft industry standards for ASAS

- Determine how to provide ADS-B/ASAS information to equipped aircraft about non-equipped aircraft (F3)

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2.7.6Experimentation and Validation PhaseOf course, this phase is essential. It includes validation through real-time simulations involving pilots and controllers and also flight trials.

The validation process should measure the potential benefits and constraints but also the associated controller and pilot workloads.

At this stage, it is possible to conduct more in depth cost/benefit analysis addressing partial and progressive equipage of the fleet.

Similarly, the safety of the ASAS applications needs to be proven.

After some iterations, the ICAO standards and the industry standards should be finalised by the end of this phase.

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Transition Issues

Experimentation and Validation Phase

- Validation of the selected ASAS applications through real time simulations (A1)

- Validate the new airspace boundaries and organisation through simulations(A4)

- Experiment and validate selected ASAS applications through flight trials (A1)

- Validate the new share of responsibility between pilots & controllers (A3)

- Finalise ICAO standards for selected ASAS applications (A2)

- Measure potential benefits & constraints through real-time simulations (B1)

- Re-evaluate the cost/benefit analysis (B2)

- Demonstrate the benefits of early equipage (B3 & F4)

- Conduct a full safety study taking into account human factors (C1)

- SSA to demonstrate that the system and their elements, meet the safety objectives and requirements (C6)

- Evaluate the ASAS procedures and contingency procedures (D5 & D8)

- Validate the ‘New ‘Rules of the Air’ and the airborne separation minima (D6 & D7)) through simulations

- Evaluate the tools necessary for the ground system for ASAS operations (D2 & D4)

- Measure controller & pilot workloads during real-time simulations (D10)

- Evaluate pilot workload during flight trials (D10)

- Validate and update controller and pilot training programmes (D11)

- Evaluate the compatibility between the ASAS and ACAS procedures during flight simulations (D9)

- Validate ASAS algorithms through real-time simulations (E2)

- Evaluate ASAS algorithms during flight trials (E2)

- Test the ASAS equipment or airborne architecture for the integration of ASAS functions (E1 & E4)

- Test the compatibility between ASAS and ACAS through real-time simulations (E5)

- Measure the performance of the selected ADS-B media architecture through flight trials (E7 to E19)

- Experiment and validate the ASAS HMI (E20 to E23)

- Finalise ICAO technical standards for ASAS (E2 & E3)

- Finalise industry standards for ASAS

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2.7.7Implementation PhaseThis phase is not part of the RTD plan but should be the result of a successful RTD plan.

The following table does not include any more tasks to be conducted but questions which should be positively answered before ASAS implementation.

Transition issues identified in the earlier phases are of paramount importance.

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Transition Issues

Implementation Phase

- ICAO standards for ASAS applications are approved (A2)

- The new airspace boundaries and organisation are in place (A4)

- Regulations on operational procedures are in place in Europe (A1)

- The potential benefits should become real (B1)

- The constraints should be kept minimum (B1)

- Implementation costs should be as publicised (B2)

- The safety should be maintained or increased (C1)

- The ASAS procedures and contingency procedures are clearly defined (D5 & D8)

- The tools necessary for the ground system for ASAS operations are implemented (D2 & D4)

- Controller & pilot workloads are acceptable (D10)

- Controller and pilot training programmes are in place (D11)

- ACAS is still an independent safety tool (D9)

- ICAO technical standards for ASAS are approved and compatible with ACAS standards (E2, E3 & E5)

- Industry standards approved by the Certification Authorities

- ASAS equipment or airborne architecture for the integration of ASAS functions are suitable for a wide range of aircraft (E1 & E4)

- The selected ADS-B media architecture has the suitable performances (E7 to E19)

- Enough aircraft are fitted with ASAS equipment (F1)

- ASAS applications are practical in MAS (F2)

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2.7.8RTD Plan scheduleIt is difficult to define a schedule to achieve the proposed RTD plan.

The best estimates proposed by the EMERALD/WP5 partners are the following:

Schedule (in years)

TSA applications

TC applications

SC applications

User Requirement or Concept Phase - 1 1

User Requirement Analysis or Feasibility Phase 0.5 1 2

Functional Requirement or Acceptability Phase 0.5 2 3

ASAS Development or Prototyping Phase 1 3 5

Experimentation and Validation Phase 1 3 3

Total duration 3 10 14

The rationale of the proposed values is driven by several factors:

- The ASAS application classes are a key factor for the duration of the RTD plan. Indeed, the Traffic Situation Awareness applications are the easiest applications to address.

- The proposed values are considered as optimistic even if in some instances the phases can overlap. For example, the validation phase of the TC applications can range from 3 to 6 years depending on the selected applications (e.g. the validation of the closely spaced parallel approach application is seen as very difficult).

- Conducting at the same time the RTD plan for the three classes of ASAS applications will lead to a duration of at least 14 years but probably more.

- The ASAS application classes are not comparable because they will lead to different benefits:

- the TSA applications will improve the level of safety in specific airspace but cannot provide increased capacity or better flexibility on their own;

- the TC applications will improve capacity and provide better flexibility in MAS;

- the SC applications will provide better flexibility in FFAS.- For one class of application, the project duration could be shortened if the

number of selected ASAS applications is small.


It was not feasible within the EMERALD project to evaluate the efforts (in man-years) necessary to complete the tasks for the following reasons:

- too many assumptions needed to be made in areas like operational strategy, technical options, economical and political decisions;

- the necessary resources were not planned within the project.

2.7.9Other remarks on the RTD planThe tasks identified in each RTD phases are not ordered by priority nor in a sequential order. A project plan for each phase of the RTD plan will need to be established by a project leader. There are several solutions depending on the project structure and the number of partners. The operational and technical expertise required to conduct such a project is tremendous because it encompasses the ground and the airborne sides. The word ‘co-operative’ implies a lot of challenges and the participation of many actors.

It is true to say that many tasks described in the RTD plan have been already undertaken by various bodies. Several projects are underway in Europe and in USA and most of them are technology driven. Trials and experiments have been conducted.

The In-Trail Climb procedure conducted in the US oceanic airspace is a good example to show that going to fast may lead you to a ‘dead end’ where further evolution is not possible. The current procedure is performed with passenger carrying aircraft showing some degree of maturity. A limited number of airlines are participating due to the lack of international consensus. There are few opportunities to use this procedure and thus the potential benefits are not real. The US industry wanted to use a collision avoidance system (TCAS II) for a purpose for which it was not designed. Pilot associations, controller associations and States were strongly opposed to the international standardisation of this procedure.

There is an essential need for an internationally approved operational concept for ASAS and operational requirements for ASAS applications.

Finally, there is another risk for the aircraft industry if ASAS applications are not treated coherently, to be faced with the multiplication of systems and the difficulty to integrate them.

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3Discussion

3.1The approach to WP5WP5 is divided into five tasks, each one building upon the previous, ending with the results sanctioned by the user’s community. Users from communities representing the interests of ground ATM system owners and operators, aircraft and equipment manufacturers, airline operators and pilots have been consulted.

Some individuals involved in WP5 are active members of international organisations enabling first-hand information and expertise to come into the WP. Each partner is involved in all the stages of WP5, so their expertise in particular areas was used by allocating them work pertaining to WP5 in these areas.

3.2Management of the tasks

3.2.1WP5.1The first task consisted of identifying the potential application scenarios for ADS-B/ASAS. Results from WP1 defining the baseline scenario had to be kept in mind during this stage. In a first step, the partners made a document review, compiling all the potential ADS-B/ASAS applications they could find in the available literature and/or other projects.

The limited time and resources available for the WP5 prevented the partners from applying the assessment study to every potential application. It was found necessary to restrict the list to a small number. To that end, the applications were classified according to several criteria: time-scale, type of airspace and expected benefits (airspace capacity, flight efficiency and safety). After a discussion, eight representative and promising applications were chosen as a restricted list.

At that stage, the partners needed a more complete understanding of user needs, and of the preliminary requirements. To that end, a description of the eight applications has been performed using a template developed by SICASP. Two of these areas were filled in to help and describe the eight applications : Definition, and Benefits & Constraints. This process leads us to select three applications for a more in depth analysis.

The main criterion for selecting the three applications was that they presented the broadest range of characteristics. The assumption was that it would be possible to generalise at a later stage the results of the assessment.

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3.2.2WP5.2The second task consisted of assessing the selected ADS-B/ASAS applications

The SICASP ASAS template was reused as it offered a broad range of domains in which to assess the applications. At this stage, each partner was allocated domains according to their expertise. Thomson and Sextant worked on the technical areas for all three applications. DERA, NATS and SOFREAVIA, each dealt with one application addressing the operational areas.

The work itself was accomplished in two identical cycles made of the following stages:

- The partners filled as completely as possible the template;- Then, the work was reviewed by other partners.

3.2.3WP5.3The third task consisted of gathering user’s feedback on the previous work.

A copy of the draft WP5.2 report was sent to a list of attendees with a letter of invitation to the user’s interview. The list of potential attendees was established by the partners and it included people working on other relevant European projects.

The user’s interview was held on 17 November 1997, hosted by CENA in Toulouse. Thirty six people were present, although a lack of airline users was noticed.

During the meeting, the partners presented their results followed by a question/answer session. The WP5.2 report was then modified to take into account the user’s contribution (approval, comments and criticisms) and ultimately sent to the users with copies of the presentation aids.

3.2.4WP5.4The fourth task consisted of making a final assessment of the suitability of ADS-B techniques for ASAS, and producing a study program highlighting the ADS-B/ASAS issues. The same pattern of work sharing as in WP5.2 was reused, and a constant review process ensured the consistency of the assessment.

During the EMERALD/WP5 progress meeting 3, a brainstorming session on the main domains of the RTD plan was organised. A draft RTD plan was written, which each partner reviewed and expanded until a satisfying result was achieved.

3.2.5WP5.5The fifth task consisted of seeking approval and criticism from the users on WP5.4 work. A draft WP5.4 report was sent to the user’s community (the people who were invited at the user’s interview, even if they did not attend). They were invited to send their comments, on the relevance of the assessment, and on the RTD plan issues. Their contribution was integrated into the WP5.4 report, which became the WP5.5 report and was mailed to the users’ community.

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3.3Discussion of the results

3.3.1Genericity of the ASAS applicationIt was necessary to generalise the results obtained at the early stages (WP5.1-WP5.3) on the specific applications. An advantage of this approach was to give several levels of operational and technical requirements.

Nevertheless, the classification may not be the only valid one. For other purposes than the assessment to be made in this study, other categorisations might be envisioned.

It has to be noted that the ADSP (Automatic Dependent Surveillance Panel) has selected two services, respectively corresponding to TSA and TC applications (refer to section 10.3).

- Traffic Situation Awareness Service: The provision of information to the flight crew to convey the status, position and where possible, the intention of other traffic with respect to their own trajectory.

- Co-operative Separation Service: A service where a set of actions, automatic or manual , which have a clearly defined operational goal, and begin and end with an operational event, during which time the responsibility of separation between aircraft is delegated to the pilot.

During its meeting in December 1997, the ADSP decided not to create a service corresponding to the SC applications because it was thought that there was no operational requirement for such a service.

The generic classification may present some flaws. The major one is that the limits between the classes might be fuzzy in some cases.

Furthermore, the classification is more operationally oriented than technically. So the classes do not necessarily reflect an increase in the technical complexity of the ASAS equipment.

3.3.2Global assessment of the ADS-B techniques for ASAS applicationsThis assessment aimed at providing the partners with enough elements on two ADS-B techniques (STDMA and 1090 MHz Mode S), in order to compare their features with the ASAS requirements. The difficulty there (and the major risk for the study) was to work on features which are not completely stable, and/or for which up to date data was difficult to get.

This global assessment is limited to two communication media, and does not consider other technologies such as Universal Access Transceiver, UAT and Range Applications Data Link Subsystem, RA DLS, which are also emerging.

3.3.3RTD PlanThe RTD plan depends on the relevance of the previous analyses. It is derived from the issues highlighted by the generic application description and by the global assessment of selected ADS-B techniques. Nevertheless, it has undeniable qualities : its approach is broad-based (all domains are considered) and defines a progressive and realistic programme.

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4Conclusions

There is a need in Europe for a coherent approach to address these issues. Currently, it seems that we are progressing in a ‘Brownian movement’. As a caricature, there are no operational requirements for ASAS applications while techniques are proposed on the market. The difficulty lies with the fact that we need the expertise of various bodies within Europe. Because of the lack of common approach, each body is trying its own way.

The situation is similar within ICAO where several panels are involved. Co-ordination is required to avoid duplication of efforts and misunderstanding.

There is a requirement from the aircraft industry and the aircraft operators that ASAS concept be approved and implemented on a world-wide basis. International co-operation is again essential.

If the proposed RTD plan is conducted as a co-ordinated programme with the necessary resources and expertise, the target dates indicated in the Eurocontrol document ‘ATM Strategy for 2000+’ [3] could be achieved:

- 2008: Limited separation responsibility transfer;- 2015: Extended separation responsibility transfer.

Nevertheless, several uncertainties can affect the ASAS concept development:

- the RTD plan shows that there is much work still to be done;- the estimated timescales may prove to be conservative;- the requirements/interest in ASAS applications will determine the most

technically suitable ADS-B techniques and timescales;- the estimated timescales should meet ATM 2000+ timescales if the RTD plan

is started immediately.

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5Recommendations

Recommendation WP5 - 1

It is recommended that the RTD plan devised during the course of this project be used as a guide for further research into the ASAS domains by the RTD funding authorities.


It is recommended that the RTD activities described in the RTD plan be undertaken quickly in order to cope with the EATMS schedule for ‘Co-operative ATM.


It is recommended that co-ordination between all organisations involved in ASAS studies be undertaken.

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6Appendix A - Longitudinal Station Keeping

6.1Definition

6.1.1Operational purpose of the applicationThis application will allow aircraft on one track to maintain longitudinal separation 1 in an in-trail stream. The aim of ASAS would not be to reduce the separation minima which are determined by current radar standards but potentially to reduce actual separations below those currently achieved. The aim is to increase capacity by reducing controller workload. The responsibility for overall separation remains with the controller, but a transfer of responsibility for station keeping with the lead or 'master' aircraft is given to the pilot of the following or 'slave' aircraft.

The stream would consist of a sequence of aircraft pairs (i.e. a stream of 3 aircraft would consist of 2 aircraft pairs. In this case the middle aircraft would follow the lead aircraft, and the last aircraft would follow the middle aircraft). Each pair of aircraft would consist of a ‘master’ and a ‘slave’ aircraft.

The aircraft selected for station keeping may be required to have similar performance characteristics. If station can only be kept by similar performance aircraft then it may also be possible to station keep during climb/descent.

In order to maintain separation whilst in a stream it may be necessary for the following aircraft to vary the separation from the lead aircraft within a certain tolerance. There is an issue regarding whether a small or large tolerance may be required. It may be necessary to allow the following aircraft to operate within a volume of airspace, or ‘bubble of uncertainty’. The requirement for this may arise from the performance limitations of the following aircraft. In practice, it may be detrimental to the following aircraft if it is required to throttle forwards and backwards, in order to maintain a very ‘fixed’ separation.

The concept of the ‘bubble of uncertainty’ is complementary to the moving bubble concept for RNP.

Whilst it is likely that the lead aircraft will be maintaining a prescribed (ATC) speed, it is not clear whether the following aircraft in the stream would/will be required to maintain its separation by time, distance or speed, although TCAS performance is based on ‘time to closest approach’ and the moving bubble RNP concept is also based on time. Further consideration must also be given to whether the separation of the following aircraft is controlled by the pilot, or is an autopilot function.

6.1.2Type of airspaceEn-route radar airspace.

To prevent conflict between station keeping traffic and other traffic it is desired that the stream should operate in exclusively reserved airspace without crossing traffic. Therefore all crossing traffic would be excluded from the stream. The exception to this

1 Elsewhere in this document references to ‘separation’ mean ‘longitudinal separation’ unless otherwise stated

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may be crossing military traffic, which would be treated as an exception or emergency procedure.

6.1.3Applicability to IFR and VFRThis application would be used in airspace where IFR applies.

There would be no operational benefit in VFR airspace as there are currently no capacity restrictions in European VFR airspace. The ASAS equipment and associated CDTI equipment may provide some benefit in VFR airspace, but would not be used for station keeping. This is an indirect benefit, and beyond the scope of this study.

6.1.4Required aircraft separation minima5 NM as in current en route radar airspace. The aim would be to reduce actual separations below those currently achieved, rather than reduce current separation standards. Achieving this would lead to more efficient use of airspace.

6.2Benefits and Constraints

6.2.1Benefits anticipated from the application

6.2.1.1Common- Increased capacity by reducing currently achieved separation levels.

6.2.1.2ATC- By treating a stream of aircraft as a single aircraft this may reduce controller

workload.- A secondary benefit is if aircraft are segregated based on their performance

characteristics, then they may be easier to manage.

6.2.1.3Pilot- The presentation to the pilot - using a CDTI - of the station keeping scenario will

increase the pilot’s situational awareness.- The display of Flight ID will mean that unambiguous identification of an aircraft is

possible.- The use of a CDTI for improved situational awareness may increase the pilot’s

confidence.

6.2.1.4Airline- It may be possible to improve the reliability of flight times (planning & reducing

delays).- By flying aircraft together of similar performance it may be possible to optimise

the flight profiles.- By flying aircraft more closely together, and on optimum routes it may be possible

to achieve fuel savings.

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6.2.1.5ATS providers- Increased capacity by more efficient air traffic management

6.2.2Constraints and limitations

6.2.2.1Common- Common ATC procedures (across national boundaries) may need to be modified.- Airspace structure may require modification to allow specific airspace for station

keeping application and emergency procedures.- Partial equipage (within the same airspace) of ASAS equipment may mean that

within medium term timescales there are too few ASAS equipped aircraft of similar performance on the same route to establish a stream. Pairwise Station keeping may be necessary in early implementations.

- By allowing aircraft to fly more closely together this may increase capacity in one specific area. However, the end to end capacity of the route needs to be considered or ‘bottlenecks’ may be created, and the capacity benefit will be forfeited. The Closely Spaced Parallel Approach application could be one answer to this problem.

6.2.2.2ATC- Treating a stream of aircraft as a single entity - for the purposes of station keeping

- may result in some actual or perceived loss of the full air picture, with regards to an individual aircraft in the in-trail stream. A controller assistance tool may be required.

- The perception of the pilots having more autonomy may result in reduced controller confidence in their own authority,

- The handover of a stream to another sector may result in an increase in workload for both the ‘handing-over’ and the ‘receiving’ controller,

- The interaction or cross over of military traffic may cause increased controller workload, e.g. the controller will be required either to clear a route for military traffic through the stream or direct the military traffic around the stream.

6.2.2.3Pilot- This application requires the pilot to be more aware of the air picture, and maintain

separation from preceding aircraft. Therefore pilot workload is likely to increase.

- The pilot will need to aware of the limitations of CDTI with respect to it providing a full and accurate air picture.

- There may be an increase in TCAS nuisance alerts because TCAS operates on time to closest approach, and alerts can occur even at relatively large separations if the closure rate is large.

6.2.2.4Airline- There may be increased equipage costs to those airlines who decide to equip with

ASAS equipment.

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- The training of pilots to perform station keeping will result in extra costs to the airlines.

- Segregated airspace may be considered as disbenefit to non-equipped aircraft who are unable to fly in ‘station keeping’ airspace.

- Airlines may consider it commercially sensitive to exchange data between aircraft from other carriers.

6.2.2.5ATS provider- The current ATC display of air traffic may require modification, and

augmentation.- The training of controllers to manage station keeping.- There may be ground infrastructure costs relating to providing information about

non-ASAS equipped aircraft to ASAS equipped aircraft.- A controller assistance tool may be required.- The current design of airspace may prohibit the effective use of airspace for station

keeping.- If PRNAV2 is implemented aircraft may fly more closely spaced parallel routes.

This may limit the airspace availability when there is an emergency in the stream, requiring an aircraft to leave the stream laterally.

- Several ATCCs (from different States) may be required to co-operate in this application to allow the stream to travel a reasonable distance.

- There may be issues associated with providing demonstrably equitable charges to equipped and non-equipped aircraft.

- It may be difficult to justify different levels of service given to station keeping and non-station keeping aircraft.

- Potential competition for airspace.

6.3Safety AssessmentThis type of operation is covering the en route phase with ATC.

The following operational procedures are to be defined with respect of safety criteria:

- co-ordination between ATC and pilot.- correct concurrent use of the ASAS and TCAS functions.- correct display of the relevant data to the pilot per flight situation.

6.3.1Integrity assessmentThe longitudinal station keeping ASAS function has to work without ground redundancy but with the TCAS and pilot redundancies.

Any undetected failure of the longitudinal station keeping ASAS function can induce a significant reduction in safety margins or a pilot recovery with significant increase in workload.

The risk assessment is major on the longitudinal station keeping ASAS application.

The longitudinal station keeping ASAS function has to face:2 Precision area navigation (PRNAV) is intended to enable aircraft to navigate with much greater accuracy, and therefore to allow lateral tracks to be more closely spaced than the current radar separation minima.

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- reception of undetected erroneous tactical data from the aircraft or the surrounding traffic.

- undetected loss of the conflict detection function.- undetected malfunction of the separation manoeuvre elaboration.- undetected display of erroneous data to the pilot.The integrity requirement is 10 -5 /h on the longitudinal station keeping ASAS function.

On the basis on the ASAS integrity estimation given in the chapter 2.3 of [4], this objective seems reachable by the ASAS function.

6.3.2Global collision risk assessmentFor this type of enroute operation where the aircraft are obliged to follow dedicated tracks and where they have less airspace than during autonomous aircraft operation, the absolute collision risk is estimated at 1 per 1000 flight hours.

The target level of safety is 10-9 per flight hour.

In the following table, the global collision risk assessment is given for the ASAS single channel case.

Availability IntegritySafety Target 10-9 10-9

ASAS 10-3 10-5 Absolute collision

risk10-3 10-3

Global collision risk without backup

10-6 10-8

Required backup 10-3 10-1

We see in this table the need for a back-up surveillance mean.

This backup can be, for an availability problem, an other ASAS channel, an ATC surveillance through radar with ATC separation standards.

For an integrity problem, the backup can be either the other independant ASAS channel or the TCAS or the surrounding aircraft. With an independent navigation means, the integrity improves by a factor 10-5.This is not the case with the satellite segment of the GPS. But a corresponding improvement of the integrity by a factor of 10-2 is reasonable

In the following table the global collision risk assessment is given for the dual channels ASAS function.


Dual ASAS 10-3 x 10-3 = 10-6 10-5 x 10-2 = 10-7 Absolute Collision

Risk10-3 10-3

Global Collision Risk without backup

10-9 10-10

Required backup 1 1

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We see that the dual channels ASAS function is satisfying alone the safety target.

6.4Data RequirementsData requirements will be described alongside the Operational procedures which include several aspects:

6.4.1Joining or establishing the stream:The controller must be aware of both master (aircraft 1) and slave (aircraft 2) Aircraft identification, flight plan, position, velocity and intents to properly monitor the stream joining by the slave Aircraft.

Additional « tools » may have to be made available to the controller in order to provide automatic data comparison between two Aircraft. The controller after checking the opportunity of this manoeuvre between the two Aircraft, will issue a LSK clearance to aircraft 2 which will include at least the following information:

- Identification of the master Aircraft(aircraft 1)- Separation minima (and tolerances) between Aircraft, (in time or distance) - Instructions to aircraft 2 to join the stream, and perform LSK with aircraft 1. It

may include: joining point, and time to joining point (or speed instruction to meet the joining point within a certain time).

- Duration of the LSK. Controller to provide aircraft 2 with a waypoint where LSK will be completed.

Aircraft 2 must be aware of Identification, position, velocity and intents of aircraft 1 in order to maintain the self-spacing function and to know when it will have to disestablish the stream.

The stream joining could be done by aircraft 2 pilot in a semi-automatic way, he would be required to enter a few parameters (joining point, time...) and to let the auto-pilot proceed. It means that aircraft 2 must be fitted with the « tools » allowing the joining process in an efficient manner considering Aircraft performances and economic parameters.

The stream joining could be done in a manual way, the pilot adjusting the Aircraft speed to meet the controller requirements. This may not be the optimal solution with regard to the pilot workload and economic factors.

6.4.2Maintaining the separationThe pilot is requested to maintain for example a 5 NM separation minima.

Aircraft 2 must be aware of Identification, position, velocity and intents of aircraft 1.

Aircraft 2 must be fitted with separation monitoring « tools » connected to the auto-pilot and based on velocity changes or on position information.

As the controller retains the responsibility of separation between Aircraft, conformance of aircraft 2 trajectory within the constraints of the stream has to be made available to him.

The ATC system will have to monitor the Aircraft LSK performances. This will be performed by establishing a comparison between radar data and ADS-B messages

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transmitted by aircraft 2 (Identification, Position, Velocity). This function has to be made available in the control centre.

6.4.3Leaving or disestablishing the streamThe controller breaks the pairing aircraft 1/aircraft 2 within the stream and establish a new pairing between aircraft 1 and aircraft 3. Same data (as joining or establishing the stream) have to be exchanged between Aircraft and between Aircraft and the ATC. If the controller wants aircraft 3 to close the « gap » with aircraft 1, joining instruction will have to be transmitted.

6.4.4Handing over a stream to an other sector

6.4.4.1Ground-ground data exchange:Handing over a stream to an other sector is much more complex than the handing over of a single Aircraft. It requires specific information to be exchanged between the 2 controllers:

- Number and category of Aircraft in the stream- Separation (and tolerances) between each Aircraft- Duration (up to which waypoint) of the LSK for each Aircraft

6.4.4.2Air-ground data exchange:It is unlikely that the current procedures would be modified. The fact that a stream of Aircraft are performing LSK may not alleviate the individual handing over of each Aircraft.

6.4.5Emergency proceduresIn case of emergency, the controller will disestablished the current LSK procedure with

the conflicting Aircraft and insure the separation requirements with its current surveillance tools (radar...).

No specific data exchange are expected to be required.

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Summary of data requirements for LSK :

Aircraft needs

ATSneeds

IdentificationCall Sign R RAddress R RCategory n/r RState VectorHorizontal Position R RVertical Position R RHorizontal Velocity R RVertical Velocity R n/rTurn Rate R n/rSpeed Change Rate n/r RNUCP ,NUCR R RStatus and IntentEmergency/Priority Status n/r RTCP n/r RTCP+1 n/r n/r

R = Required

n/r = not required to support the indicated ADS-B application, but may be used to improve the performance of the application.

NUCp = Navigation Uncertainty Category / position

NUCr = Navigation Uncertainty Category / velocity

Alert time 2 minPosition error 20 m / 30 ftVelocity error 0.25 m/s / 1 fps

6.5Data Link Requirements

6.5.1Risk allocationRefer to the safety assessment

6.5.2Impact of position and velocity measurement error on warning timeWithin [5], some simulations have been performed, which do not correspond to the LSK application, but the figures obtained, can give preliminary idea on the datalink requirements.

- They conclude that the impact on the warning time due to position error less than 40 metres was of little effect. In addition a velocity standard deviation of less than 3 m/s appears to be adequate.

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- The requirement on the update period is of course dependent on the probability of update of the communication Medium within the considered environment. It appears that the required update period would be of 0.5, 1, 2, or 3 seconds if the update probability is respectively 0.35, 0.5, 0.8 or 0.95.

6.5.3Summary of datalink requirements for LSK

Station Keeping

State Vector Acquisition Range

40 nmi

Mode Status Acquisition Range

40 nmi

On Condition Acquisition Range

n/a

Availability Dual 10-6 Single 10-3

Integrity <10-6 Latency < 1,5sNominal Update Period <= 10 s

Notes:

Some supporting analyses for update period and update probability are provided in Appendices J and M of [5].

Acquisition range correspond to an engineering judgement and more generally all information on datalink constraints are requiring additional specific assessment and should not be limited to currently available literature.

6.5.4Safety analysis consequences on the datalink requirementsThe safety analysis demonstrated that in the case of a detected failure, a backup efficiency of 10-3 will be required to perform LSK operations in the case of a single onboard ASAS configuration.

In the case of a dual onboard ASAS configuration, the air-air ADS-B datalink has to be doubled.

No specific air-ground datalink requirement is foreseen to be implemented, as this application is assumed to be performed under radar environment. A 10-3 reduction risk factor is currently accepted as being the ATC intervention efficiency.

6.6Pilot Interface Requirements

6.6.1Human factors aspectsNeed of the pilot assessment of the overall situation.

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6.6.2Display requirementsA CDTI display will be necessary i.e. a display enabling the pilot to see the surrounding aircraft, to select one/several aircraft and to get flight information about these aircraft.

The relative distance and the relative speed with the preceding aircraft has to be materialised on the display.

Visual aids could be useful to indicate:

- the preceding aircraft capture procedure (speed, acceleration/deceleration rate), based on aircraft performance),

- the preceding aircraft speed following procedure: maintain Xnm +/- ?nm between two aircraft, with X= 7nm +/- 0,5nm for instance.

- the preceding aircraft speed change following procedure: need of co-ordination between the two aircraft.

- the standby or recapture procedure after stream leave by the preceding aircraft.The following skeleton display illustrates the preceding specific LSK display requirements where the Aircraft has to follow an aircraft at a distance of 20 Nm in 10 mn:

Its target speed and its target track are supposed to be computed by the ASAS application and followed either by the pilot or the autopilot.

30Nm

520kts

400kts

LSK in 10mn

6.6.3Aural indicationsNot required for normal operations (only required in case of unforeseen event (manoeuvre of the other aircraft) or of wrong manual procedure).

6.6.4Failure and mode selection indicatorsNo specific requirements.

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6.7ATC Interface RequirementsThe ATC interface will be required to provide the controller with information that will enable him to manage the five process steps given in Section 1.1. It is likely that new controller assistance tools will be required to help him safely monitor the established stream whilst treating a stream of aircraft as a single entity. If the controller establishes a stream at a certain flight level, and gives the lead aircraft a specific speed to follow, then the stream will have a common flight level and speed. As the stream achieves a generic flight profile the controller may lose his full situational awareness of the trajectory of an individual aircraft. The real or perceived situational awareness may be further reduced by the pilot’s ability/permission to operate in a ‘bubble of uncertainty’.

When the stream is being established, or a single aircraft is joining the stream, the controller may need specific information about the aircraft approaching the stream. It may be necessary to predict when an individual aircraft will reach the stream so that the controller directs the aircraft with minimum disruption to the rest of the stream. This function may be similar to the arrival sequencing of aircraft into a final approach. However, further work may be required to determine the accuracy of the information required, as well as what information is required.

As the controller retains the responsibility of separation between aircraft, one function of the ATC system may be to show the controller the conformance of the aircraft trajectory within the constraints of the stream. The system task will be to monitor the aircraft within the stream, and to control the stream. The data that will be required by the ATC system is:

- Aircraft type/performance- Longitudinal separation required- Flight level/barometric altitude- Proposed separation from parallel/lateral tracks- Area of airspace designated for station keeping - How many aircraft in stream (e.g. by marking the lead and end aircraft so that the

boundaries of the stream are unambiguous). This data is particularly relevant during the handover of a stream to another sector.

- Places where aircraft may enter or leave an already established stream. This may be a way point or junction en route.

The controller display may be required to show:

- Conformance of lead aircraft with intended trajectory.- The ATC system (i.e. the controller) may need to mark the lead aircraft position

and the end aircraft position in order to define the boundaries of the stream being controlled

- The display will need to show the separation that has been set- Separation monitoring alerts.- Aircraft intentionally breaking away from station keeping due to emergency etc.

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6.8Operational ProceduresThere are several aspects of operation for the station keeping application, which require distinct procedures.

1. The first of these is joining or establishing the stream. The initial join of the 'slave' aircraft to the 'master' aircraft may be difficult. ATS must be aware of the 'master' aircraft's intentions in order to allow the 'slave' to be easily guided into position.

2. The second of these is maintaining separation. Separation is maintained by the slave aircraft and separation is followed within a ‘bubble of uncertainty’ for each aircraft where each aircraft can vary their separation from the aircraft in front within certain tolerance. Speed control is imposed on the lead aircraft and advised to the succeeding aircraft in the stream. A controller assistance conformance monitor may alert the controller to any deviation from the required flight profile within the stream.

3. The third of these is leaving the stream or disestablishing the stream. The controller breaks the pairing within the stream and new pairing is established across the ‘gap’ left by the departing aircraft. It is unlikely that the remaining aircraft would close the gap. Instead, a new separation would be established between the new pairing which is approximately twice the value of the original pairing. This prevents undue stress on the performance of the slave aircraft (as well as the following pairs of aircraft), in a ‘catch up’ manoeuvre.

4. The fourth of these is the task of handing over a stream to another sector. Complete details of the stream is communicated between the sectors during the handover.

5. Another aspect of station keeping is the emergency procedures that may be required during any time in the station keeping application. In an emergency either an emergency descent or a lateral manoeuvre to a ‘hard shoulder’ would be required. The lateral manoeuvre may conflict with closely spaced parallel routes, and this manoeuvre requires further consideration. Current en route lateral separation standards require 10 NM separation. As with the ‘leaving the stream’ the remaining aircraft in the stream will maintain a new pairing across the ‘gap’.

6.8.1Actions and responsibilities taken by the pilot and the controllerController

- Decides which aircraft are suitable for station keeping.- Issues instructions to the aircraft to assume responsibility for station keeping. - Gives desired spacing interval from preceding aircraft, and its callsign,

heading, distance, and altitude to the following aircraft. Pilot

- Accept station keeping option.- Must correctly identify the preceding aircraft and maintain the self-spacing

function.

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6.8.2Proposed actual separation between aircraft to be applied by the pilot during the procedureClose to radar separation. This could be greater depending on the demand for airspace i.e. in low capacity traffic the required separation could be greater than the standard requirement.

6.8.3Proposed new, or new usage of current, radiotelephony (R/T) phraseology- Acceptance/ Rejection of station keeping option.- Confirm correct acquisition of preceding aircraft, and required spacing.- May use data link to issue some of the instructions (CDPLC).- R/T or data link information between a controller and a specific aircraft may be

required by all other aircraft in the stream to maintain situational awareness about new instructions to the specific aircraft concerned.

6.8.4Limiting factors which could affect the application of the procedure- Pilots unable to maintain separation, or unhappy with maintaining minimum

separation.- Poor mix of aircraft types not suitable for station keeping.

6.8.5Controller’s responsibility to maintain a monitoring function;Controller will set up and maintain current monitoring function at a lower level of workload.

6.8.6Proposed contingency procedures.If either the controller or the pilot are not satisfied with the separation from the preceding aircraft then a break manoeuvre must be initiated. The passing manoeuvre would be preferable with the 'slave' aircraft changing altitude or track.

6.9Questions to AnswerWould it be feasible for aircraft to form pairs without controller intervention. This would significantly change the ‘Joining Procedure’, and would reduce controller workload, but would also mean that a greater transfer of data would be required between the aircraft concerned e.g. flight plan data.

It is likely that a ‘bubble of uncertainty’ would be required for each aircraft in the stream. More work is required to establish whether a small or large tolerance is operationally preferable, and also whether this tolerance varies depending on the aircraft position in the stream e.g. the last aircraft following a stream may require a larger tolerance to minimise consequences of all the other aircraft varying their relative positions to one another.

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7Appendix B - Closely Spaced Parallel Approaches in IMC

7.1Definition

7.1.1Operational purpose of the applicationThe arrival rate of aircraft at the threshold of a runway is recognised as a principal determinant of runway capacity. Arrival rate is determined by runway occupancy time, approach speed and separation.

If effective separation between aircraft on approach can be safely reduced, the runway capacity of an airfield can be raised. The factors on which to act to reduce separation (on the arrival segment) are numerous. Among them, the most relevant are :

- guidance systems. These are systems which enable pilots to position correctly their aircraft on the final approach track.

- controllers expertise. It is the ability of the controllers to give timely clearances in order to optimise runway occupancy. This expertise may be partly integrated into sequencing aid tools.

- surveillance tools. These are systems which enable controllers to visualise the situation in order to monitor the traffic and to check pilot’s conformance to his/her clearances.

The Closely Spaced Parallel Approaches (CSPA) aims at dealing with this third aspect in an airborne frame.

In IMC, the parallel runways, according to ICAO Annex 14 chapter 3 and PANS-RAC (Doc 4444) chapter 4, are divided into three categories, depending on the distance between the centre lines of the runways :

Independent parallel runways 1035 m - ¥Dependent parallel runways 915 m -1035 mSegregated parallel runways 760 m - 915 m

With independent approaches, aircraft can conduct arrivals without caring about a lateral separation with the other final approach track. The controller just ensures a longitudinal separation and that no one deviates from its track to enter a Non Transgression Zone between the runways.

With dependent approaches, the control must ensure not only a longitudinal separation but also a (diagonal) separation between aircraft on the different tracks. That leads him to arrange the aircraft in a staggered pattern.

In the segregated parallel runways, one runway is used for arrivals and the other for departures.

Due to the ground equipment performances, the different types of parallel approaches are currently conducted with a distance between runways higher than the ICAO

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recommended minima. As a first objective, the CSPA application will provide the safety required to conduct parallel approaches to the current minimum spacings.

As a second objective, the CSPA will enable to conduct independent and dependent parallel approaches with lowered minimum spacings between runways. That is, independent approaches could be done where before only dependent approaches were conducted and dependent approaches could be conducted where before only segregated approaches were conducted.

For independent and dependent approaches, the CDTI would help pilots to stay on their track and to detect any blunder. For dependent approaches, staggered approach positions would be maintained by the pilot behind using CDTI. In case of error or navigation blunder, the CSPA will help the pilot to prevent a collision hazard.

This procedure could be an alternative to the Precision Runway Monitoring3 (PRM).

7.1.2Type of airspaceThe CSPA application is designed for terminal airspaces.

Potential airports in Europe with the physical layout to make CSPA possible could include: Amsterdam/Schiphol, Berlin/Shönefeld, Hannover/Langenhagen, Cologne-Bonn/Cologne, London/Heathrow, Rome/Fiumicino and Frankfurt. This list is not definitive and is likely to lengthen due to planned construction of dual runways in Europe.

7.1.3Applicability to IFR and VFRCSPA will be applicable in IFR.

VFR are supposed to ensure their separation visually, so the CSPA procedure is not needed for them.

7.1.4Required aircraft separation minimaThe minimum separation between similar aircraft was historically determined by:

- the ability of radar systems to distinguish between aircraft on approach and to update displayed information sufficiently frequently

- views on the required height at which a following aircraft could safely abort a landing in the event of failure to clear the runway by the leading aircraft.

- the communication constraints: the radio link has to be available in time to issue instructions to the aircraft.

- the phenomenon of wake vortices.Wake vortices are rotating air masses created at the wing tips of an aircraft during flight, and are caused by dynamic lift. Through friction with the surrounding air, the energy of the wake vortices decreases with a certain gradient. Therefore, the lifetime of the vortices will differ depending on their initial energy. They move downwards with a

3 The PRM system was developped on the initiative of the FAA to reduce the necessary spacing of parallel runways for simultaneous independent approaches under Instrument Meteorological Conditions. It consists of:

- an improved radar- a high resolution colour display for the controllers.

The PRM system could accomodate 3400ft (1035 m) spaced parallel runways.

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vertical speed and also drift horizontally according to wind speed and direction. Thus, the staggered aircraft could be affected by wake vortices of another on the other track.

For avoiding wake vortices, the following separations are recommended by ICAO (Doc. 4444), depending on the mass of the aircraft :

Leading aircraft:/Following aircraft: Heavy Medium Light

Heavy (> 136000 kg) 4 NM 5 NM 6 NM

Medium (7000 kg - 136000 kg) 3 NM 3 NM 5 NM

Light (< 7000 kg) 3 NM 3 NM 3 NM

Furthermore, ICAO recommends in Doc. 4444 a diagonal separation of 2.0 NM between aircraft on parallel dependent tracks.

The longitudinal minimum separation between aircraft on the same final approach track is defined in Doc. 4444 as 3 NM in standard conditions and can be reduced to 2.5 NM under specific conditions (see Part VI - 7.4.2)

The longitudinal separation targeted by the CSPA procedure are the minima recommended by ICAO. As the wake vortices are responsible for a degradation of the minimum separation which could be required, the staggered and longitudinal separation to be adopted in the CSPA application will depend on the crosswind parameters.

7.2Benefits and Constraints

7.2.1Benefits

7.2.1.1ATC- By relieving the controller of some separation assurance tasks, this may reduce

controller workload. Indeed, the controller will no more have to issue speed regulation and radar vectoring instructions. He would control less and monitor more, the latter function being presumably lessdemanding.

- The capacity is increased by reducing lateral separation requirements between runways during simultaneous parallel approaches. At present, ICAO considers that independent parallel approaches may be conducted with runway spacings as low as 3400 ft (1035 m) [6]. However, usual radar systems allow only parallel approaches with runway spacing as little as 4300 ft (1310 m) using current procedures [7]. This figure may be reduced to 3400 ft (1035 m) with new systems such as a Precision Runway Monitor system. With ASAS/ADS-B providing the pilot with a separation monitoring facility, parallel runway spacings may be reduced to 3000 ft (915 m) or less.

For example, the following is a very simplified calculation. Considering a single runway where Heavy (approach speed 140 kts - B747) and Medium (approach speed 125 kts - A320) categories aircraft land in a random pattern. This gives the following table of time separation required between each aircraft, according to each possible pair (H-H, H-M, M-H, M-M):

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Leading aircraft/Following aircraft Heavy Medium

Heavy 3600*4/140 = 103s 3600*5/125 = 144s

Medium 3600*3/140 = 77s 3600*3/125 = 86s

Assuming a hypothetical probability of 25% for the arrival of each pair, the single runway capacity is

3600/(103*.25 + 144*.25 + 77* .25 +86*.25) = 35 moves per hour

Now, lf the airport manager builds a parallel runway next to the previous one, with 915 m between the centre lines due to surface contingency. This is a dependent parallel runway. The pair of aircraft arrive now in a staggered pattern, with a diagonal separation of 2.0 NM, which gives a longitudinal separation of D = 2*Ö((2.0 NM)2 - (915 m)2) = 3.88 NM which we round to 4 NM for simplicity’s sake.

915 m

2 NM 2 NM

D

Consequently, the minimum separation between two successive aircraft on the same track becomes 4.0 NM.

The new matrix of time separation is then :

Leading aircraft/Following aircraft Heavy Medium

Heavy 3600*4/140 = 103s 3600*5/125 = 144s

Medium 3600*4/140 =103s 3600*4/125 = 115s

With these figures, we get the following parallel runways capacity:

2*3600/(103*.25 + 144*.25 + 103* .25 +115*.25) = 61 moves per hour

The theoretical capacity improvement, due to CSPA applied with the doublet, is (61/35 - 1) = 74 %. Of course, the real figure will be lower because of unavoidable contingencies such as go-arounds.

If the airport authority had two dependent parallel runways then CSPA may enable independent approaches. In this case, the theoretical capacity improvement, due to CSPA applied with the doublet, is (2*35/61 - 1) = 14.8 %. Once again, the real figure will be lower. Even if this figure seems low compared to the previous one, the advantage here is that there is no need building another runway.

The previous benefits are mutually exclusive because increasing capacity implies more sequencing work which would negate the reduction in workload.

7.2.1.2Pilot- The use of a CDTI for improved situational awareness may increase the pilot’s

confidence

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7.2.1.3Airlines- If CSPA is applied to increase capacity on a congested it will be possible to

improve the reliability of flight times (planning & reducing delays).- If CSPA is applied to increase capacity on an uncongested airport, more flights

will be possible.

7.2.2Constraints

7.2.2.1ATC- The CSPA application must keep the safety at its current level- Common ATC procedures (across national boundaries) may need to be modified;- It may be necessary to modify the sequencing tools where they exist.- Delegating some degree of legal responsibility to an aircraft for the purposes of

CSPA may result in some actual or perceived loss of the full air picture, with regards to an individual aircraft. Furthermore, the perception of the pilots having more autonomy may result in reduced controller confidence in their own authority. It is a human factors problem.

- The current ATC display and flight plan processing system of air traffic may require modification. In addition, a recovering assistance tool may be necessary.

- Controllers will need training to manage CSPA.- The CSPA application will be performed only in radar-monitored approaches due

to the necessity for the controller to be able to deal with missed approaches and recovering capability.

- The CSPA might not give benefits for airports with only one IAF (Initial Approach Fix) because, operationally, sequencing the aircraft, in order to maintain radar separation (3 NM or 1000 ft between two aircraft) before the Final Approach Fix (FAF), may increase the controller’s workload to such a point that it negates the benefits expected from CSPA. The following picture drawing explains the configuration of this type of approach:

FAF

FAF

IAF

7.2.2.2Pilot

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- This application requires the pilot to be more aware of the air picture, and maintain separation from preceding aircraft. Therefore pilot workload will increase.

- The pilot will need to be aware of the limitations of CDTI with respect to it providing a full and accurate air picture.

- The imprecision of the aircraft and ground navigation systems used in simultaneous parallel Instruments Landing System approaches can cause aircraft to inadvertently enter the No-Transgression Zone (NTZ). This implies that both aircraft be equipped with sufficiently precise guidance systems.

- There may be an increase in TCAS nuisance alerts because TCAS operates on time to closest approach.

Let’s take a simple example. A and B are flying at 220 kts, with a angular speed of 3 degrees per second (standard turn) and are separated by less than 600 ft because of a mistake either from the pilot or from the controller. The approaches are independent.

d

B

AFAF

FAF

-R

r

R

NTZ

The distance r between the two aircraft is r= 2R(1-sin) + d

The closure speed r’ between the two aircraft is r¢ = 2Vcos

For a distance d = 1035 m, the worst ratio r/r’ is equal to 14 seconds (for = 54 degrees) which is inferior to the TCAS triggering threshold for an RA (20 seconds for the 2350ft to FL50 layer). This RA is not triggered if d is at least equal to 2550 m.

Obviously, this proves that the closest the runways are, the better the aircraft guidance must be to avoid intempestive RAs.

7.2.2.3Airlines- There may be increased equipage costs to those airlines who decide to equip with

ASAS equipment

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- The training of pilots to perform closely spaced parallel approaches will result in extra costs to the airlines

7.3Safety AssessmentThis type of operation is covering the TMA airspace.

The following operational procedures are to be defined with respect of safety criteria.:

- co-ordination between ATC and pilot during all the operation;- correct concurrent use of the ASAS and TCAS functions;- correct display of the relevant data to the pilot per flight situation.

7.3.1Integrity AssessmentThe Closely Spaced Parallel Approaches ASAS function has to work in IMC conditions with TCAS, and ATC redundancies.

Any undetected failure of the Closely Spaced Parallel Approaches ASAS function can induce a large reduction in safety margins or too high workload for accurate tasks performance by use of TCAS in emergency conditions.

The risk assessment is hazardous on the Closely Spaced Parallel Approaches ASAS application.

The Closely Spaced Parallel Approaches ASAS function has to face:

- reception of undetected erroneous tactical data from the aircraft, the surrounding traffic or the ATC;

- undetected loss of the conflict detection function;- undetected malfunction of the separation manoeuvre elaboration;- undetected display of erroneous data to the pilot.The integrity requirement is 10 -7 /h on the Closely Spaced Parallel Approaches separation assistance function.

On the basis of the ASAS integrity estimation given in the chapter 2.3 of [4], this objective is not reachable by a single channel ASAS function alone.

7.3.2Global collision risk assessmentAs far as, for this type of operation, the traffic density is higher and the weather conditions are bad,we consider an absolute collision risk of 1 per 100 flight hours.

In fact, the corresponding traffic situation is more complicated and more risky than the current approach phase one due to the reduction of separation minima with the same number of Air Traffic Controllers (no specific PRM controller, only one controller for two runways in case of dependant approaches).

The target level of safety is 10-9 per flight hour.

In the following table, the global collision risk assessment is given for the ASAS single channel case.

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ASAS 10-3 10-5

Absolute collision risk 10-2 10-2


10-5 10-7



This can be, for an availability problem, another completely independant ASAS channel with an availability of 10-3 failure per flight hour and the ATC surveillance with ATC separation standards and an availability of 10-3 . A priori there is no need of specific ATC tools.

For an integrity problem, the back-up can be the other ASAS channel which can only improve the integrity by a factor 10-5 if the navigation means are completely independent. This is not the case with the satellite segment of the GPS. But a corresponding improvement of the integrity by a factor of 10-2 is reasonable. The complementary integrity can be given either the ATC or the TCAS or the surrounding aircraft.

The corresponding table is the following one.


dual ASAS 10-3 x 10-3 = 10-6 10-5 x 10-2 = 10-7

ATC surveillance 10-3 10-5

Absolute collision risk 10-2 10-2

Global collision risk 10-11 10-14

Required backup 1 1

We see that the safety target is satisfied by the use of a dual ASAS and the ATC.

7.4Data RequirementsThe data (and datalink) requirements depend on :

- the approach procedure : Whatever is the runway spacing, dependent and independent approaches will induce different requirements, but it is likely that dependent approaches will be less demanding on surveillance system accuracy than independent approaches.

- the airborne navigation data source (« en route » like or « ILS » like). The application may need to be augmented by other functions.

7.4.1Update period and time stampingThis issue is addressed here as it is more critical for that particular CSPA application.

The pilot has to be informed immediately when an Aircraft is going to deviate from its nominal track. The controller in that case is assumed to be less efficient than the pilot otherwise the application would be considered as useless.

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To have an end to end service which could be comparable to a PRM, an update period of the ADS-B reports of 1 s would be required. In addition, the receiving Aircraft has to make sure that the time factor has not induce errors on the received data or that the errors have been compensated.

The navigation sources are making measurements periodically and provide the information to the ADS-B once per period. An end to end latency period appears (between time of measurement in aircraft 1 and time when the information is available to the aircraft 2 pilot). This latency includes measuring time, transmission to aircraft 1 ADS-B subsystem, processing into aircraft 1 ADS-B subsystem, transmission over ADS-B Medium, processing into ADS-B subsystem of aircraft 2, and aircraft 2 application processing. These time errors are partially compensated thanks to a time of applicability which is provided with each ADS-B report, but taken into account the speed of an Aircraft in the terminal phase, a 1s error on the time of applicability may induce a 100m error on the actual position of the Aircraft.

7.4.2Design constraintsThe safety assessment demonstrated that CSPA operations could not be operated without having an onboard dual configuration.

Summary of data requirements for CSPA:

Aircraft needs

ATSneeds

IdentificationCall Sign R RAddress R RCategory R RState VectorHorizontal Position R RVertical Position R RHorizontal Velocity R RVertical Velocity R RTurn Rate R RSpeed Change Rate R RNUCP ,NUCR R RStatus and IntentEmergency/Priority Status R RTCP n/r n/r TCP+1 n/r n/r

R = Required




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Closely spaced parallel approaches

Alert time 15 secPosition error 20 m / 30 ftVelocity error 0.25 m/s / 1 fps


7.5.1Risk allocationRefer to the safety assessment.

7.5.2Impact of position and velocity measurement error on warning timeWithin [5], some simulations have been performed, considering 1000 ft and 2500 ft independent parallel runways.

- They conclude that for independent approaches, the maximum position error is 20 metres RMS and that the maximum velocity error is 0.3 m/s.

In the previous table, the velocity error was indicated as 0.25 m/s.

- The requirement on the update period is of course dependent on the probability of update of the communication medium within the considered environment. It appears that the required update period would be of 0.5, 1, 2, or 3 seconds if the update probability is respectively 0.3, 0.5, 0.7 or 0.9 (these figures are given for 2500 ft runway spacing).

7.5.3Summary of datalink requirements for CSPA

Closely spaced parallel approaches

State Vector Acquisition Range

10 nmi


10 nmi


n/a

Availability Dual 10-6

Integrity 10-6 Latency < 1,2sNominal Update Period <= 1.5 s

Notes:

Supporting analyses for update period and update probability are provided in Appendices J and M of [5].

7.5.4This information on datalink requirement are requiring additional specific assessment and should not be limited to currently available literature.

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7.5.5Safety analysis consequences on the datalink requirementsThe safety analysis demonstrated that in the case of a detected failure, a backup efficiency of 10-2 will be required to perform CSPA operations in the case of a dual onboard ASAS configuration.

No specific air-ground datalink requirement is foreseen to be implemented, as this application is assumed to be performed under radar environment. A 10-3 reduction risk factor is currently accepted as being the ATC intervention efficiency.

It has to be reminded that the single onboard ASAS configuration is excluded. Please refer to the safety assessment.


7.6.1Human factors aspectsIt is required to avoid unexpected alarm of TCAS in TMA.

As far as the pilot is responsible of the airborne safety monitoring based on the ASAS display during an hazardous application, strong attention has to be given on this specific human-machine interface to avoid any airborne situation misunderstanding. The approach phase is an head-up flight phase. There is a requirement to present traffic, conflict alarms and separation maneuver orders on a head-up display. This has to be further analysed to take into account all the head-up requirements and to see their compatibility with existing Head Up Display (HUD). Only a small part of the worldwide commercial aircraft fleet is equipped with HUD. From an economical point of view, it would be difficult to justify the HUD retrofit only for an ASAS purpose on an aircraft not HUD equipped.

7.6.2Display requirementsA CDTI display will be necessary ie a display enabling the pilot to see the surrounding aircraft, to select one/several aircraft and to get flight information about these aircraft.

The CDTI should display a Non-Transgression Zone (NTZ) between the runways to help the pilot to avoid endangering the other aircraft. The approach axis should also be materialised in order to help the pilot to assess his position. In addition the display’s scale and definition should be adapted to the visualisation of a small area.

There is an issue to be raised on the NTZ. This zone is defined for air traffic controller display. For pilot display we have three different zones which can be displayed:

- the basic ASAS protection zone which is a circle around the aircraft.- the NTZ which is like a wall between the two runway axis.- the tunnels delimiting the allowed airspace for approach and landing around the

two runway axis.A geometric synthesis of these three volumes is required for a pertinent picture for the pilot.

The relative distance with the preceding aircraft has to be materialized on the display.

The following skeleton display illustrates the preceding specific CSP display requirements:

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hhh

2.5Nm

4Nm

7.6.3Aural indicationsOnly required in case of unforeseen event (manoeuvre of the other aircraft) or of wrong manual procedure.


7.7ATC Interface Requirements

7.7.1Current requirements

7.7.1.1Independent parallel approachesAccording to ICAO PANS-RAC (Doc 4444) Chapter 4, independent parallel approaches can be conducted: provided that :

- SSR equipment is as follows:- with parallel runways spaced as low as 1035 m, the SSR equipment shall

have a minimum azimuth accuracy of 0.06 degrees (one sigma), and an update period of 2.5 seconds or less and a high resolution display providing position prediction and deviation alert.

- with parallel runways spaced as low as 1310 m, SSR equipment specifications other than the foregoing may be applied when it is determined that the safety of aircraft operations would not be adversely affected.

- with parallel runways spaced of more than 1525 m, the SSR equipment shall have a minimum azimuth accuracy of 0.3 degrees (one sigma), and an update period of 5 seconds or less.

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- ILS or MLS approaches are being conducted on both runways- the aircraft are making straight in approaches- separate radar controllers monitor approach to each runway and ensure that when

the 300 m (1000 ft) vertical separation is reduced:- aircraft do not penetrate the depicted NTZ, which is 610 m wide;- the applicable minimum longitudinal separation between aircraft on the same

localizer course or MLS final approach track is maintained;Other conditions exist that are not relevant here.

7.7.1.2Dependent parallel approachesAccording to ICAO PANS-RAC (Doc 4444) Chapter 4, dependent parallel approaches can be conducted: provided that :

- a suitable surveillance radar is available with a minimum azimuth accuracy of 0.3 degrees (one sigma) and an update period of 5 seconds or less is available;

- ILS or MLS approaches are being conducted on both runwaysOther conditions exist that are not relevant here.

7.7.2CSPA requirementsThe controller will have a means to know which aircraft is capable of performing CSPA, via the strip for example, or by radio (voice or ground-air data-link).

Due to current approach radar precision, the controller might be unable to distinguish a blunder trajectory on time to act efficiently. As this feature is judged unacceptable, controllers need to be provided with more precise and more frequently updated data.

For example, with ADS-B data, ATC would monitor the ADS-B messages ensuring that an aircraft maintains conformance to its intended trajectory. The integrity of ADS-B data would be checked on-board. It could also be done via a more sophisticated approach radar.

The controller may require a separation monitoring tool. The controller, due to workload, is interested in the ‘big picture’. As ADS-B information is also available on the ground, a separation monitoring function (either automated or ATC selectable) may be used.

Although, for the time of the CSPA, legal responsibility for staggered separation has been delegated to the pilot, the controller must be able to recover the situation in case of CSPA capacity loss. Consequently, it might be judged necessary to help him with a recovering tool.

Immediately available communication between pilots and controllers is of crucial importance in the safe conduct of simultaneous parallel ILS approaches.

7.8Operational Procedures

7.8.1Actions and responsibilities taken by the pilot and the controller

7.8.1.1Current ATC procedure

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The approach controller uses his/her radar for the following purposes (Doc 4444 Part VI-9.2):

- provide radar vectoring of arriving traffic on to pilot interpreted final approach aids;

- provide radar monitoring of parallel ILS approaches and instruct aircraft to take appropriate action in the event of possible or actual penetrations of the no transgression zone (NTZ);

- provide radar vectoring of arriving traffic to a point from which a visual approach can be completed;

- provide radar vectoring of arriving traffic to a point from which a precision radar approach or a surveillance radar approach can be made;

- provide radar monitoring of other pilot-interpreted approaches;- in accordance with prescribed procedures, conduct:

- surveillance radar approaches;- precision radar approaches;

- provide radar separation between:- succeeding departing aircraft- succeeding arriving aircraft;- a departing aircraft and a succeeding arriving aircraft.

7.8.1.2Planned CSPA procedureDuring simultaneous parallel approaches aircraft are directed to the final approach courses at different altitudes separated by at least 1000 ft. This separation is necessary because the normally maintained 3 NM separation is lost as the aircraft fly toward their respective localisers. Once the aircraft are established on the parallel localiser course, the 1000 ft vertical separation is no longer maintained, and they are permitted to descend on the glideslope, flying toward the airport separated by the distance between the runways centre lines.

One monitor controller observe and monitors the final approach course, runway complex, and portions of the departure fan for the runways. The parallel runway approaches are divided into multiple zones. the No Transgression Zone (NTZ) is an area in which aircraft are prohibited to enter. It is established equidistant between the extended runways centrelines. If an aircraft blunders from the Normal Operating Zone (NOZ) into the NTZ, any endangered aircraft are turned away to prevent a collision.

The CSPA will enable the pilot to be delegated the following function: provide CSPA separation between succeeding arriving aircraft;

This delegation will apply only on the basis of an agreement between the pilot and the controller, either on a case by case basis, or on a more formal and general basis (agreement protocol between involved parties). Within this condition, the actions and legal responsibilities are the following:

Controller

- lines up the aircraft in the staggered approach pattern (if necessary, with the aid of tools)

- communicates identity and separation required to pilots

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- monitors situation in respect of separation ‘busts’.Pilot

- maintains and monitors separation from preceding aircraft using CDTI. The legal responsibility for separation starts from the time the CSPA clearance is given until the time the aircraft he separates from touches the runway or initiates a breakout manoeuvre.

7.8.2Proposed separation between aircraft to be applied by the pilot during the procedureMinimum separation recommended by ICAO.

7.8.3Proposed new, or new usage of current, radiotelephony phraseology- phraseology to give and confirm ident of preceding aircraft on pilots’ CDTI- phraseology to give and confirm required separation.- phraseology to allow pilot to action go-around on separation ‘bust’.

7.8.4Limiting factors which could affect the application of the procedureNot all aircraft on approach have functional ADS-B/ASAS equipment.

7.8.5Controller’s responsibility to maintain a monitoring functionThe controller (using a separation monitoring tool, if necessary) may demand a go-around. The legal responsibility of staggered separation has been devolved to the pilot, but the controller has right of veto.

7.8.6Proposed contingency proceduresGo-arounds on separation infringements, the same as for VFR conditions (to be more closely studied).

7.8.7ExampleTwo runways (27L and 27R) whose centre lines are 915 m (3000 ft) away are fed by two stacks. Two aircraft (A and B) are waiting in a different stack at FL60. A and B are ADS-B equipped. B is supposed equipped with the CSPA application but not necessarily A. The following drawing and the framed text describe the procedure.

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915 m

B

A

FAF 27R

FAF 27L

IAF

IAF

NTZ

CTL : ‘A cleared to leave stack for approach ILS 27Romeo. Descend to 3000 ft’

A : ‘Leaving stack for approach 27Romeo 3000 ft’

CTL : ‘A cleared to intercept ILS for final approach.’

A : ‘Cleared ILS 27 Romeo 3000 ft’

The controller sees that B and A could be in the right configuration for a CSPA approach.

CTL : ‘B traffic info aircraft A eleven o’clock 10 NM. Do you agree with a further CSPA with A traffic?’

B : ‘ASAS contact. OK for CSPA.’

CTL : ‘A, expect CSPA following approach by B traffic’

A : ‘Roger’

CTL : ‘B cleared to leave stack for approach ILS 27Lima. Descend to 4000 ft’

B : ‘Leaving stack for approach 27Lima 4000 ft’

CTL : ‘B, cleared to intercept ILS for CSPA final approach 2 NM staggered with A traffic.’

B : ‘Cleared ILS 27 Lima 4000 ft. Starting CSPA 2NM staggered with A traffic.’

From now on, the pilot of B is responsible for his separation with A. If something goes wrong, he must perform the necessary actions to avoid endangering A. The sequel to the above example can be depicted according to three cases.

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Nominal situation

A : ‘ILS 27 Lima intercepted. Final approach’

CTL : ‘A, cleared to land.’

A : ‘I land’

B : ‘ILS 27 Romeo intercepted. Final approach’

CTL : ‘B, cleared to land.’

B : ‘I land’’

Once A has touched the ground, the CSPA approach is terminated and the controller is in charge of the ground separation between B and A.

Problem with B

B, for some reason, becomes unable to perform the CSPA procedure or deviates from its nominal track without hope of recovering it on time to ensure safety. These situations could be detected by the CSPA ASAS application and an appropriate warning could be issued.

B : ‘CSPA aborted for [reason]. Going around’

The controller regains control over B and may give him specific instructions to proceed a new landing.

Problem with A

A, for some reason, deviates from its nominal track and enter the CDTI NTZ. This intrusion is detected by B who informs the controller.

B : ‘Intrusion by A. CSPA aborted. Going around’

The controller regains control over B and may give him specific instructions to proceed a new landing.

Since A deviated a lot from his track, it is highly likely that A will also make a missed-approach. In this case, the controller will have two simultaneous missed approaches to manage and could be led to apply emergency separation standards that is 2.5 NM, 500 ft, with a traffic info to both aircraft.

If A is also ASAS equipped, the two pilots will see each other electronically and will be able to avoid disturbing each other, thus reducing the risks.

7.9Questions to answerIt may be suitable to recommend an assessment of the ILS/MLS interferences due to a leading aircraft taxiing or about to land. For this last case ICAO can not apply and simulations are required before doing a precise quantitative capacity description. For D-GPS approaches this kind of study seems unnecessary.

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It will be necessary to determine whether the NTZ definition will be unique for all airports or airport-dependent

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8Appendix C : Autonomous Aircraft

8.1Definition

8.1.1Operational purpose of the applicationThe Autonomous Aircraft concept was first introduced in 1993 by the European Union’s 'Airspace and ATM concepts and Options for the Single Unified European CNS/ATM System' (ATLAS) study [8]. This concept granted autonomous control within designated airspace for airspace users, who took responsibility for flight safety. The responsibility for providing infrastructure, traffic information, contingency procedures and search and rescue remained with Air Traffic Control (ATC). In 1995, the FREER project, standing for 'Free-Route Experimental Encounter Resolution', was started at the EUROCONTROL Experimental Centre in France. As part of this work, the feasibility of delegating ATC functions to the aircraft was investigated. One of the several options examined was the Airborne Autonomous Control (AAC) mode where ATC and trajectory management functions are fully delegated to the flight deck for operations in low density airspace. This mode has been termed by FREER as ‘Autonomous Aircraft Operations’ [9][10].

The driving force behind this requirement is the possibility of allowing aircraft to fly preferred routes, and reduce costs by the reduction or removal of en-route charges.

The Autonomous Aircraft concept is far removed from the simple rules of 'see and be seen' used by aircraft in VMC, requiring specific avionics equipment including ADS-B and ASAS to be fitted to provide timely details on how to avoid other traffic. The term 'timely' is important as it changes the scenario away from a short term (and possibly rapid) change of course as would be required by ACAS, to a more fuel efficient trajectory. FREER [10] expects that the ASAS system will provide 6-8 minutes prior warning in advance of ACAS for this type of concept.

This package of work examines the FREER concept and expands the benefits, safety, and system requirements to provide an investigation into potential benefits and constraints.

8.1.2Type of airspaceThis type of operation is the driving force behind the concept of Free Flight Airspace (FFAS) as defined in the EATMS concept [2]. This will predominantly be at high level except in low to medium density traffic areas. An aircraft operating in FFAS will be required to be fitted with a minimum standard of CNS equipment and be certified for Free Flight. This investigation concentrates on the en-route phase of the flight and does not attempt to examine the benefits or drawbacks of the system in high density areas or TMAs.

8.1.3Applicability to IFR and VFR

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As mentioned earlier, this concept is superior to the simple VMC rules of 'see and be seen', the ability of the avionics suite to provide real time situation awareness and handle conflicts makes this system ideal for both IFR and VFR conditions.

FREER [9] covers the concept of Extended Flight Rules (EFR) to assign extensions to VFR and ATLAS Autonomous Flight Rules (AFR). EFR uses the surveillance data to identify the de-confliction action to be made, while taking into account the implications of economic penalties, which may be incurred. The EFR rules define which aircraft has the priority in a particular situation but does not decide on how the conflict should be avoided. The priorities are based on specific aspects of each aircraft including the manoeuvrability, the aircraft's constraints and the distance to encounter. In the en route scenario the aircraft furthest away from the point of separation must give may to the one closer. This will typically require a smaller change aircraft direction to achieve the required separation. If the range is equal then the priority is given to the more manoeuvrable.

8.1.4Required aircraft separation minimaAlthough the concept is still in its infancy and requires development to determine the detailed functionality, the use of existing or future GNSS which supply very accurate time stamped positions, provides a potential for reductions in separation, particularly in areas of existing poor radar coverage. However, it is the accuracy of trajectory prediction, efficiency of conflict probing and conflict resolution (by pilot or automatic means) and allowance for time to manoeuvre that may be the critical factors in determining the separation minima.

8.2Benefits and constraints

8.2.1Benefits anticipated from the application

8.2.1.1ATC- By providing the aircraft with flexible routing, the requirement for the aircraft to

fly together in corridors is removed. This provides the possibility of enhanced capacity due to the increase in available volume provided.

8.2.1.2Airline- During flight planning the operator can produce optimum routes through the

regions allocated as free flight. This includes the use of optimum altitudes and the use of flexible tracks to avoid adverse weather conditions. Taking advantage of these benefits, the operator would expect to experience:

- reduced fuel consumption, providing higher profits or cheaper fares depending on the market forces.

- reduced flight times, which could enhance the attractiveness of the operator to the time conscious passenger.

- By eliminating the requirement for ATC during this phase of the flight, the En-route charges will be substantially reduced. It expected however, that some fee would be required to pay for SAR services and a Flight Information Service.

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8.2.2Constraints and limitations

8.2.2.1Common- As the FFAS may operate over several national or regional boundaries the

authorisation for aircraft entering will need to be clearly established.

8.2.2.2ATS providers- A fundamental requirement of the Autonomous Aircraft concept is that the traffic

density should be such that the aircraft do not need to deconflict too often. Therefore it will become the ATS responsibility to limit the aircraft entering the region.

The entry and exit points, as well as other dynamic (weather dependent) or static choke points must be managed to prevent high levels of traffic density.

Note: The detailed investigation of the transition between FFAS and non FFAS is outside the scope of this study.

8.2.2.3ATC- Investment will be required to modify and augment ATC displays to meet the new

requirements of the concept. - New software tools may be required to control and estimate the traffic density.

This is not a trivial requirement and will require a computer model capable of estimating the trajectories of aircraft in the region, taking into account other aircraft, desired route and weather conditions.

8.2.2.4Pilot- Airspace may be required to be reserved for potential emergencies or equipment

malfunctions, which may result in Flight Levels, which are normally vacant or contain procedural traffic.

8.2.2.5Airline- There is a potential that much of the air space designated as free flight is unlikely

to represent optimum routes. For example, if the North Sea area were to be designated as FFAS, an examination of traffic density would show a high density of flight operations along the most frequently used routes, such as London to Amsterdam, and a low density in areas which do not lie near optimum routes.

- There will be increased initial cost to the operators to provide the avionics. The perceived advantages of the autonomous aircraft concept must be sufficient for the investment in equipment to be justified.

8.3Safety AssessmentThe associated flight phases are in the free-flight airspace including secondary airfields.

The following operational procedures are to be defined with respect to safety criteria:

- co-ordination between ATC and pilot during transitions at the free-flight airspace boundaries and in the free-flight airspace itself.

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- correct concurrent use of the ASAS and TCAS functions.- correct display of the relevant data to the pilot per flight situation.

8.3.1Integrity assessmentThe autonomous aircraft ASAS function has to work without ground redundancy but with the TCAS as safety net which is intentionally not considered in the following analysis.

Any undetected failure of the autonomous ASAS function can induce a significant reduction in safety margins or a pilot recovery with significant increase in workload.

The risk assessment is major on the autonomous aircraft ASAS application.

The autonomous aircraft ASAS function has to face:

- reception of undetected erroneous tactical data from the aircraft or the surrounding traffic.

- undetected loss of the conflict detection function.- undetected malfunction of the separation manoeuvre elaboration.- undetected display of erroneous data to the pilot.The integrity requirement is 10 -5 /h on the autonomous aircraft ASAS function.

On the basis of the ASAS integrity estimation given in the chapter 2.3 of [4], this objective seems reachable by the ASAS function.

8.3.2Global collision risk assessmentThe concepts of airways and tracks are not applicable during autonomous aircraft operations. Also the absolute collision risk is lower in case of complete system failure because the aircraft are more equally spread in the airspace.

In free flight airspace the basic collision risk in case of complete failure of airborne systems can be estimated at 10-3 per flight hour.

The target level of safety is 10-9 collision per flight hour.

In the following table the global collision risk assessment is given for the ASAS single channel case.


ASAS 10-3 10-5 Absolute collision

risk10-3 10-3


10-6 10-8



This can be, for an availability problem, an other ASAS channel, an ATC surveillance through ADS SATCOM. It has to go with emergency clearance procedure or alarm broadcast.

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For an integrity problem, the back-up can be the other independant ASAS channel. As far as the satellite segment of the GPS navigation means is common to the two ASAS channels, the integrity of the dual ASAS cannot be better than 10-7. Alternative backups are the TCAS or the surrounding aircraft.

In the following table the global collision risk assessment is given for the dual channels ASAS function.


Dual ASAS 10-3 x 10-3 = 10-6 10-5 x 10-2 = 10-7 Absolute collision

risk10-3 10-3


10-9 10-10

Required backup 1 1

We see that the dual channel ASAS function is satisfying alone the safety target.

8.4Data RequirementsData requirements will be described alongside the Operational procedures which include several aspects:

8.4.1Approaching free-flight area- Pilot to check ADS-B equipment in operations.

Display with OK status of AA application and ADS-B subsystem.

- Pilot to request entry into free-flight area.The pilot transmits Identification (call sign, address and category), position, Navigation Uncertainty Category and its expected trajectory to the controller, using long-distance datalink communication Medium.

- Controller to clear Aircraft into free flight area and AA operations.The controller provides the Aircraft with long term traffic prediction and AA clearance to the Aircraft for a pre-determined airspace. The controller is assumed to use long-distance datalink communication Medium.

8.4.2Autonomous Aircraft operation:

8.4.2.1Long term operations :An Aircraft (or the airline having an Aircraft) entering free flight airspace may require to have a long term view of the traffic which could induce conflicts on its route, to optimise its route or flight profile. The « long term » view will depend on the duration of the Autonomous Aircraft operation and the duration of the flight. It may be reasonable to consider a 30 minutes traffic overview for continental flights and few hours for long haul flights.

This would require Airlines Operation Centres, AOC, to be interconnected to the Air Traffic Services (Control Centres or Central Flow Management Units) for two reasons:

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- to provide the detailed flight profiles which have been loaded into Aircraft FMS to the ATS. An other scenario would be to consider that each Aircraft which plans to perform AA operation must transmit to the ATC its long term intents. In that case, the most likely solution would be to use addressed datalink between the Aircraft and the controller.

- to have access, under ATC control, to the long term view of the traffic that its AA may have to face.

By having the knowledge of the « long term » foreseen traffic in the free flight airspace, the airline will compute an optimal long term route and flight profile taken into account the traffic constraints and the Aircraft performances to optimise flight time and fuel consumption, and uplink an optimised « free flight profile » to its Aircraft.

8.4.2.2Short term operation :At short term (up to 5 to 10 minutes) , the AA will use the information contained in the ADS-B messages from the other participants.

For separation insurance, the Aircraft will exchange their accurate trajectory, conflict configuration and resolution process using their broadcast or addressed capabilities. We may assume that broadcast could be used during routine transmission, but that during conflict resolution between two Aircraft addressed datalink may be required. The safety assessment may demonstrate that an additional (independent) mean may be requested to validate the broadcast information.

Several functions will be involved and various data will be required.

- Conflict Detection : potential conflicts, will be highlighted by a detection process which will require as input Identification, State Vector and Intent information from all involved Aircraft.

- Conflict Resolution : the resolution process will take into account the « Rules of the Air » which may have to be extended or refined and the data (same as above) transmitted by the other Aircraft. Rules of the air will have to provide the key principles of the deconflicting procedure. These rules may assign only one Aircraft to perform the manoeuvre or assign interactive rules and manoeuvres to both Aircraft what may not prevent one Aircraft to be responsible for the manoeuvre and to provide first resolving instruction. New Intents will be computed and exchanged between Aircraft.

- Manoeuvre Performing : the conflict configuration and the new conflict-free trajectory is proposed and displayed to the pilot who is requested to validate the intents. An interface to the auto pilot is required to automatically perform the manoeuvre if the pilot does not want to do it manually.

Separation Insurance Monitoring : the master Aircraft will monitor the convergence of the separation insurance process taken into account any potential new events.

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Summary of data requirements for AA :

Aircraft needs

ATSneeds

IdentificationCall Sign R RAddress R RCategory R RState VectorHorizontal Position R RVertical Position R RHorizontal Velocity R n/rVertical Velocity R n/rTurn Rate R n/rSpeed Change Rate R n/rNUCP ,NUCR R RStatus and IntentEmergency/Priority Status n/r RTCP R RTCP+1 R R

R = Required




Alert time 4.5 min(6 min)

Position error 20 m / 30ftVelocity error 0.25 m/s / 1fps


8.5.1Risk allocationRefer to the safety assessment

8.5.2Impact of position and velocity measurement error on warning timeWithin [5], some simulations have been performed, the figures obtained, can give preliminary idea on the datalink requirements.

- They observed no decrease in the warning time as a function of position data errors. Fairly high velocity errors (about 6 m/s) were also adequate to provide acceptable warning time.

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- The requirement on the update period is of course dependent on the probability of update of the communication Medium within the considered environment. The table below is given the acceptable update period with related update probability.

Update Period Update probability

7 0.95

6 0.9

5 0.85

4 0.7

3 0.6

2 0.45

1 0.25

0.5 0.15

8.5.3Summary of datalink requirements for Autonomous Aircraft

Autonomous AircraftState Vector Acquisition Range

120 nmi (note 1)


120 nmi (note 1)


120 nmi (note 1)

Availability Dual 10-6 Single 10-3

Integrity 10-6 Latency < 1,5sNominal Update Period <= 10 s

Notes:

1) The 120 nmi range requirement applies in the forward direction. The required range aft is 40 nmi The required range 90 degrees to port and starboard is 60 nmi.

Some supporting analyses for update period and update probability are provided in Appendices J and M of [5], but additional simulations would be required to confirm and refine these figures.

8.5.4Safety analysis consequences on the datalink requirementsThe safety analysis demonstrated that in the case of a detected failure, a backup efficiency of 10-3 will be required to perform AA operations in the case of a single onboard ASAS configuration.

This backup may be provided by :

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· Another independant channel of ASAS function including the Navigation means, the transponders and the ASAS core. This multiplies by two the ADS-B datalink requirements in term of frequency capacity.

· An addressed datalink (through SATCOM) between the aircraft and a ground ADS station. The ground ADS station is assumed to be fitted with all required separation monitoring tools to inform the controller on time of any potential conflict. It means that the separation between the aircraft have to be sufficient to allow the ATC recovery.

· Specific procedure have to be defined in order for the aircraft which detected a failure in its ASAS function, to leave the AA airspace.

· A specific Alarm mode could also be applied to inform the surrounding aircraft of the incapability of the aircraft to perform AA operations. This could be done by voice communications.

The safety analysis demonstrated that in the case of a undetected failure, a backup efficiency of 10-1 will be required to perform AA operations in the case of a single onboard ASAS configuration.

The critical phase would be in the conflict detection and conflict resolution phase. In that case it is assumed that all aircraft will be fitted with a specific tool in their ASAS application to monitor if the other aircraft have properly detected and resolved any potential conflict.


8.6.1Human factors aspectsNeed of the pilot assessment of the overall situation.

8.6.2Display requirementsA CDTI display will be necessary for enabling the pilot to see the aircraft and the surrounding aircraft positions or relative positions, to select one/several aircraft and to get flight and flight plan information about these aircraft.

From a high level point of view, Autonomous Aircraft operations cover ASAS Crossing Procedure (ACP) and In Trail Climb/Descent (ITC/ITD) equivalent procedures in free-flight airspace. These procedures can be different from the basic ones. The Autonomous Aircraft display requirements are the synthesis of the display requirements for these procedures.

Data to be potentially displayed are a priori the following ones, for each selected aircraft:

- flight ident;- relative altitude;- relative bearing;- relative range;- closure rate;- ground speed;- ground track indication;- potential conflict status, if required

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- conflict resolution assistance data

The following skeleton display illustrates the preceding specific AA display requirements in the case of a crossing procedure:

The head of the arrows represent the aircraft position 3mn in the future. The conflicting aircraft is on the left and flying at 490kts. It should be indicated in red. The proposed deconflicting trajectory is on the left on the active trajectory and should be indicated in green.

dFL0!3:10s

490kts

410ktsFL310

8.6.3Aural indicationsNot required for normal operations (only required in case of unforeseen event (manoeuvre of the other aircraft) or of wrong manual procedure).


8.7ATC Interface RequirementsIn the Airborne Autonomous Control Mode, the responsibility for safe separation belongs to the pilot. However, the controller is required to limit the number of aircraft in the FFAS, and control aircraft as they enter and exit. In addition, in the interests of safety, the controller should act in a monitoring role the information is available. This will require the following information to be available:

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8.7.1Separation and conflict monitoring (where available).As aircraft separations reduce, the controller can monitor any change of trajectories and check that minima are not breached. This would require software tools optimised to show the intentions of the aircraft and automated warnings to predict when limits would be exceeded.

8.7.2Aircraft intentions.The controller monitors the aircraft's intentions, to check its exit time and position and monitors expected traffic density.

8.7.3Number of aircraft in area.In order to manage the flow of aircraft from ‘Gate to Gate’ and encompass in a more global way the transitions from TMA through Managed Airspace into Free Flight Airspace and back, the controller must monitor the density of aircraft either for the entire route or for sub zones, and authorise according to the traffic density expected during the passage of the aircraft. This phase would be a refinement of the planning phase, where the Airline Operations Centres (AOC) would allocate the flight profile in advance. The profile may be reviewed just before take off to take into account dynamic information such as weather. This would require Airlines Operation Centres to be interconnected to the Air Traffic Services (Control Centres or Central Flow Management Units) for two reasons:

- To provide the detailed flight profiles, which have been, loaded into aircraft FMS to the ATS. Another scenario would be to consider that each aircraft, which plans to perform AA operation, must transmit to the ATC its long-term intents. In that case, the most likely solution would be to use addressed datalink between the Aircraft and the controller.

- To have access, under ATC control, to the long-term view of the traffic that its AA may have to face.

8.8OPERATIONAL PROCEDURES

8.8.1Actions and responsibilities taken by the pilot and the controllerPilot

- checks ADS-B equipment in operation (Display with OK status of AA application and ADS-B subsystem).

- requests entry into free-flight area.- transmits Identification (call sign, address and category), position,

Navigation Uncertainty Category and its expected trajectory to the controller, using long-distance datalink communication Medium.

- deconflicts with aircraft in free flight airspace.- requests exit from free flight airspace.

Controller

- clears Aircraft into free flight area and AA operations.

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- provides the Aircraft with long term traffic prediction and AA clearance to the Aircraft for a pre-determined airspace. The controller is assumed to use long-distance datalink communication Medium.

- clears aircraft into non-free flight area and normal operations.

8.8.2Proposed separation between aircraft to be applied by the pilot during the procedureThe concept is still in its infancy and requires some work to determine the precise characteristics. The use of existing or future GNSS provides very accurate time stamped positions providing a great potential for reductions in separation, particularly in areas of existing poor radar coverage. However, it may be the accuracy of prediction of the other aircraft trajectories, and allowance for time to manoeuvre that may be the critical factor.

8.8.3Proposed new, or new usage of current, radiotelephony phraseology;Whilst in autonomous operation the aircraft would not require any communication with ATC. However, during the entry and exit from the Free Flight Area some additional communications will be required. Given that the concept represents a highly integrated system, it would be expected that all routine communications would be performed over the datalink. However, this does not exclude the possibility of using standard R/T techniques as a backup

The following communication protocols would be required;

- Acceptance / rejection of entering free flight area.- Acceptance / rejection of entering autonomous operation.

8.8.4Limiting factors which could affect the application of the procedure;The possibility of localised points of high density within the free flight airspace may cause large numbers of aircraft to deconflict. The conflict may be a long term one, caused by the crossing of preferred routes or short term caused by the aircraft changing track to avoid bad weather.

8.8.5Controller’s responsibility to maintain a monitoring function;Although the tactical decision making process has been devolved to the pilot, the controller will maintain a monitoring function in a more strategic sense.

8.8.6Proposed contingency procedures.In circumstances where equipment fails, the aircraft may be required to cease operating autonomously and / or change flight level to non-optimum altitudes, which are controlled procedurally and are not part of the FFAS. During such a transition, the ACAS would be used as a final safety net. It is important to note that the use of ACAS should not be reflected in any level of safety assigned to this concept, but only used should the other contingency procedures fail, as per other ATM concepts.

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9Acknowledgements

We wish to acknowledge the attendees of the User’s View meeting for their inputs:

- Advanced Aviation Technology;- Aerospatiale;- Air France;- Airbus;- Alcatel / ISR;- Dassault Electronique;- Eurocontrol.

This meeting was held in Toulouse on the 17th November 1997 as part of the WP5 plan. Its aim was to enable the views of ATM community to be incorporated at an early stage.

We further wish to acknowledge the assistance of Aerospatiale and Swedavia for their contributions in reviewing the RTD issues and the associated RTD plan.

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10References

1EMERALD/WP5/SOF/001/4.0 - WP5 Project Plan - Version 4.0 produced on 4 September 1997

2EATMS Operational Concept Document - Eurocontrol - EATCHIP Doc : FCO.ET1.ST07.DEL01 - Issue 1.0 - 1 March 1997

3ATM Strategy for 2000+ - Eurocontrol - EATCHIP Doc : FCO.ET1.ST07.DEL02 - Issue 1.0 - 1 October 1997

4WP5.3 report : Feasibility assessment of selected ADS-B/ASAS applications and User’s Interview

5RTCA MASPS for ADS-B Draft 6.0 - August 1997.6ICAO Annex 147ECAC APATSI Document on medium term air traffic control procedures and

techniques - August 19958Airspace and ATM concepts and Options for the Single Unified European CNS/ATM

System. (ATLAS study) - June 19939Initial Investigation into the Autonomous Aircraft Concept - Duong, Hoffman,

Nicolaon - June 1997.10FREER: Free-Route Experimantal Encounter resolution Initial Results.- Proceedings

of the 10th European Aerospace Conference on Free Flight - Vu N. Duong, October 1997.

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11List of Symbols

dB deciBel

dBm déciBel milliWatt

ft feet

fps or ft/s feet per second

h hour

Kbps kilobits per second

m metre

MHz megaHertz

m/s metre per second

NM or nmi nautical mile

s second

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12List of Abbreviations

AA Autonomous Aircraft

ACAS Airborne Collision Avoidance System

ACP ASAS Crossing Procedure

ADC Air Data Computer

ADS-B Automatic Dependent Surveillance - Broadcast

ADSP Automatic Dependent Surveillance Panel

AFR Autonomous Flight Rules

ASAS Airborne Separation Assurance System

ATC Air Traffic Control

ATM Air Traffic Management

ATS Air Traffic Services

CAA Civil Aviation Authority

CDTI Cockpit Display of Traffic Information

CENA Centre d’Etudes de la Navigation Aérienne

CNS Communication, Navigation and Surveillance

CSPA Closely Spaced Parallel Approach

DERA Defense Evaluation Research Agency

EATMS European Air Traffic Management System

EC European Community

EFR Extended Flight Rules

EMERALD EMErging RTD Activities of reLevance for ATM concept Definition

EUROCAE European Organisation for Civil Aviation Electronics

FFAS Free Flight Air Space

FHA Functional Hazard Assessment

FMS Flight Management System

FREER Free-Route Experimental Encounter Resolution

GNSS Global Navigation Satellite System

GPS Global Positioning System

HMI Human Machine Interface

HUD Head Up Display

ICAO International Civil Aviation Organisation

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IFR Instrument Flight Rules

ILS Instrument Landing System

IMC Instrument Meteorological Conditions

IRS Inertial Reference System

LSK Longitudinal Station Keeping

MAS Managed Air Space

MASPS Minimum Aviation System Performance Standards

NATS National Air Traffic Services

NEAN North European ADS-Broadcast Network

PRM Precision Radar Monitoring

PSSA Preliminary System Safety Assessment

QoS Quality of Service

RA DLS Range Applications Data Link Subsystem

RGCSP Review of the General Concept of Separation Panel

RNP Required Navigation Precision

RTCA Radio Technical Commission for Aeronautics

RTD Research and Technical Development

SC Strategic Co-operative (ASAS application)

SICASP SSR Improvement and Collision Avoidance Systems Panel

SSR Secondary Surveillance Radar

STDMA Self-organised Time Division Multiple Access

SSA System Safety Assessment

TC Tactical Co-operative (ASAS application)

TCAS Traffic alert and Collision Avoidance System

TCP Trajectory Change Point

TIS Traffic Information Service

TIS-B Traffic Information Service Broadcast

TMA Traffic Manoeuvring Area

TSA Traffic Situation Awareness (ASAS application)

UAT Universal Access Transceiver

VFR Visual Flight Rules

VHF Very High Frequency

VMC Visual Meteorological Conditions

WP Work Package

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