Surveillance Applications Policy – ASAS

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Surveillance Applications Policy – ASAS

46TH ANNUAL CONFERENCE, Istanbul, Turkey, 16-20 April 2007

WP No. 93

Surveillance Applications Policy – ASAS

Presented by TOC

Summary

Many changes have occurred to Airborne Separation Assistance System (ASAS) since 2003, when the provisional IFATCA policy on ASAS and Cockpit Display of Traffic Information (CDTI) was accepted in Buenos Aires (Argentina). It is therefore more than appropriate to do a full review of policy in order to make sure that the statements remain correct and are still up-to-date. The aim of this working paper is to inform the IFATCA – delegates and MAs about where we stand in the matter of ASAS. Clear and unambiguous policies must be adopted so that the Federation’s representatives can fully participate in the discussions where the integration of the ASAS- technology and –applications into the ICAO-process are decided.

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Introduction

1.1 Well before ICAO has started to undertake the extensive efforts to integrate and regulate the use of ADS-B (Automatic Dependent Surveillance – Broadcast) into chapter 8 of ICAO PANS-ATM Doc 4444 the difficulty to achieve this properly was identified by all stakeholders. In particular by the various ICAO Panels that were working on the subject. By now firm proposals are circulating for consultation so that it is more than likely that, by the end of year 2007, the ICAO Standards and Recommended Practices (SARPs) for ADS-B surveillance will be finalized and fully implemented. The most likely system to feed Airborne Separation Assistance System (ASAS) with surveillance data is without any doubt ADS-B. But despite the fact that both systems look alike they are definitely not the same. In the ICAO-circular, in paragraph 2.2.3, it is stated that although ADS-B and ASAS are similar systems they should not be confused. This statement is fully supported by IFATCA.

1.2. From the beginning one of the difficulties encountered was that the terms of ASAS and ADS-B were often mixed so that they almost became synonyms in the minds of many. This brought a lot of confusion to the debate and many uncertainties appeared during the stakeholder discussions. It is true that ASAS is largely dependant on ADS- B surveillance input in order to function properly. But it is well conceivable to have an ASAS-system that is using other surveillance data inputs which are not ADS-B based. For instance Traffic Information Service – Broadcast (TIS-B) is a valid alternative to ADS-B.

1.3. Another important point with ASAS is that many new operators are brought into the process. They are expected to be using ATM-surveillance data as this is well in line with the eleventh ICAO Air Navigation Conference (ANC 11) – resolutions and – conclusions where the term “operator” was approved by ICAO. New participants, such as pilots and personnel not holding Air Traffic Control (ATC) licences will be using the new surveillance data becoming available. This will bring new challenges to the system and new safety issues that need to be addressed. These changes are very significant and, as our Federation is fully taking part in the ASAS-implementation process it is necessary that the delegates and Member Associations (MAs) have a full understanding of the problems and issues at hand. By approving strong policies for the correct and safe implementation of ASAS, the Federations’ representatives will be provided with the required backing that will enable them to influence the stakeholder consultation process and expected to end in a not too distant future by ICAO publishing well structured and safe ASAS-SARPs.

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Discussion

2.1. From the very beginning when feasibility studies and planning related to ASAS started, there was a mix of terminology used in regards to ADS-B and ASAS. Through a cooperative effort between Eurocontrol and the Federal Aviation Administration (FAA) the principles of operation for the use of ASAS were laid down in 2001. The document received the title “Principles of Operation for the use of Airborne Separation Assistance Systems” (PO-ASAS). To be noted that back in 2001 the second “A” stood for “Assurance” whereas today it is for “Assistance”. One of the guiding principles of PO-ASAS was that no changes in the separation responsibilities were required for the proposed ASAS-applications.

2.2. PO-ASAS was organised into three working clusters or packages:

Package 1 has the following applications:

Airborne Traffic Situational Awareness Applications (ATSA)
Airborne Spacing Applications (ASPA)
(Note: time frame 2008-2012)

Package 2 is composed of:

Airborne Separation (ASEP)
(Note: time frame 2010-2015)

Package 3 is foreseen to be:

Airborne Self-Separation (SSEP)
(Note: time frame 2015-2020)

Ground surveillance (ADS-B) applications have been included into Package 1. Runway Incursion Alerting applications have been included into Packages 2/3.

The ASAS ground applications (GS), all part of ASAS package 1, are:

ATC surveillance for en-route airspace (ADS-B-ACC)
ATC surveillance in terminal areas (ADS-B-TMA)
ATC surveillance in non-radar areas (ADS-B-NRA)
Airport surface surveillance (ADS-B-APT)
Aircraft derived data for ground tools (ADS-B-ADD)

These applications are aimed at improving ATC surveillance in the air and on the airport surface and at enhancing the ATC tools through the use of aircraft derived data.

Seven ASAS airborne applications (AS) were defined (all part of ASAS package 1):

Enhanced traffic situational awareness on the airport surface (ATSA- SURF)
Enhanced traffic situational awareness during flight operations (ATSA- AIRB)
Enhanced visual acquisition for see & avoid (ATSA-S&A)
Enhanced successive visual approaches (ATSA-SVA)
Enhanced sequencing and merging operations (ASPA-S&M)
In-trail procedure in oceanic airspace (ASPA-ITP)
Enhanced crossing and passing operations (ASPA-C&P)

The last AS-application, ASPA-C&P was added at a later stage to Package I. With PO- ASAS, back in 2001, this item was defined as a category II application but there continues a heated debate amongst experts where to classify this particular ASAS- application. The airborne applications (AS) are now divided into four situational awareness applications and three airborne spacing applications.

2.3. Further developments in the R&D (Research and Development) domain continued to happen since the publication of PO-ASAS. In particular in Europe the CASCADE (Co- operative ATS through Surveillance and Communication Applications Deployed in ECAC) project and the work produced by ASAS Thematic Network (ASAS-TN) are of interest. The CASCADE project is managed by Eurocontrol and took up the principles of PO-ASAS and made a lot of refinements and adaptations to it. It must be stressed that it is a much larger project than just ASAS. For instance CPDLC and datalink forms also part of CASCADE, as well as other future developments such as D-FIS (Flight Information Service via Datalink). The timeframe of CASCADE is set from 2008 to 2011 and Eurocontrol sees the following planning for the future ADS-B and ASAS applications:

The first stream, called “STREAM 1” is planned from 2008 onwards and consists of four ground surveillance applications that are all based on the use of 1090 Extended Squitter (ES). The second stream, STREAM II consists currently of five airborne surveillance applications. But this might change as CASCADE clearly says that the programme is very flexible and also very dynamic. It is expected that “the list of Stream I and Stream II applications will be defined during the programme development phase and are subject to appropriate validation, business case and safety cases”.

2.4. The current CASCADE planning looks as follows: the new CASCADE Stream I consists now of only 3 GS-applications as some re-organizing of the applications has occurred. A new category, named “ATC Surveillance for radar areas” (ADS-B-RAD) appeared and the two PO-ASAS applications ADS-B-ACC and ADS-B-TMA for en- route airspace and terminal areas were merged into it. The aircraft derived data for ground tools was changed to ADS-B-APT.

For Stream II of CASCADE many changes occurred when comparing it to PO-ASAS:

“Enhanced traffic situational awareness on the airport surface (ATSA-SURF)” still remains the same as initially planned in 2001.
“Enhanced traffic situational awareness during flight operations (ATSA-AIRB)” is now newly divided into the following 5 sub-categories:
- Enhanced flight operations related to other traffic
- Enhanced visual acquisition for see-and-avoid (S&A)
- Enhanced Traffic Information Broadcast by Aircraft (E-TIBA)
- Enhanced visual separation on approach (ATSA-VSA)
- Enhanced sequencing and merging operations (ASPA-S&M)

Note: there are further applications in CASCADE Stream II but they are not directly linked to ASAS as they are more related to communication or datalink.

2.5. All ASAS GS applications have been initially classified under ASAS but, when examining them more closely, they are clearly ADS-B surveillance applications. ICAO and Eurocontrol define ASAS as:

“An aircraft system based on airborne surveillance that provides assistance to the flight crew supporting the separation of their aircraft from other aircraft”

Notes:

– it is recognized that separation from other hazards is also of importance, but these are beyond the scope of the assistance provided by an ASAS.

-assistance provided to the flight crew by an ASAS may be limited to the provision of relevant flight information concerning surrounding traffic. More automated decision support may also exist through an ASAS that provides advice to the flight crew to maintain instrument-based separation”

IFATCA believes that this is an understandable starting point. However, when ASAS will be used for separation, the separation from traffic will have to take into account all other hazards (as defined under conflict management in the ICAO Global Air Traffic Management Operational Concept Document 9854). So, the current ICAO- definition of ASAS does not fully include all that is needed. Many of the previously mentioned future ASAS-applications clearly don’t fall anymore under ASAS. According to ICAO Manual of Air Traffic Service (ATS) Data Link Applications Document 9694 ADS-B is defined as:

“[the] transmission of parameters, such as position and identification, via a broadcast mode datalink for use by any air and/or ground users requiring it”.

It’s true that ASAS requires some form of surveillance capability to function. So, the decision to include ASAS under surveillance is very reasonable. ASAS however does not require a particular type of surveillance (for example ADS-B). What ASAS needs in particular is quality (for instance accuracy or latency) of surveillance as this is a key part of surveillance when a separation service is provided to the users.

The Federation has always been very careful of not limiting ASAS to a particular type of surveillance, but to keep it as general as possible. This was done by concentrating our policies on high level statements defining the requirements of surveillance for a particular application instead of going down into too much detail. IFATCA has taken a very broad interpretation of surveillance as the Federation defines surveillance as:

“the acquisition and monitoring of objects’ positions and/or other relevant data for the purpose of Air Traffic Management, such as identity, movement and intent”.

This approach is to include not only ADS but also multilateration and other new forms of surveillance. The policy also recognizes that it can be system surveillance data (not just ATC surveillance data), as surveillance information can also be used by pilots and systems (for example by Airborne Collision Avoidance Systems (ACAS)).

2.7. The use of surveillance by air traffic controllers is not included within the current definition of ASAS. The following definition is used by PO-ASAS:

“Airborne Separation Assurance System (ASAS) is “an aircraft system that enables the flight crew to maintain separation of their aircraft from one or more aircraft, and provides flight information concerning surrounding traffic”.

The definition of an ASAS-application is:

“A set of operational procedures for controllers and flight crews that makes use of the capabilities of Airborne Separation Assurance Systems to meet a clearly defined operational goal”

(Note: Assurance now to be changed to Assistance)

ASAS-applications are further subdivided into Airborne Traffic Situational Awareness (ATSAW). These ATSAW-applications are aimed at enhancing the flight crews’ knowledge of the surrounding traffic situation.

2.8. As a Federation representing operational Air Traffic Controllers, IFATCA focuses its policy statements mainly on ATC perspective. At the last IFATCA Conference in Kaohsiung (Taiwan) there were discussions to divide surveillance into “Ground Surveillance functions” and surveillance used by airborne operators, called “Airborne Surveillance functions”. It was recognized that airborne surveillance applications can be divided into three groups: information, instructions and separation. A fourth type of airborne surveillance is “collision avoidance” but this needs to be explored further as this is certainly not part of Layer 2 of conflict management where the separation provision takes place.

The division of Airborne Surveillance Applications

2.9. “En-route ATM for IFR-traffic” is nowadays subdivided into two distinct modes of operation: Radar and procedural control. The implementation of ASAS in the air and the availability of ADS-B data on the ground will bring profound changes to this long- standing constellation. The implementation of some of the ASAS-procedures currently proposed by focus groups working on ASAS is not that distant anymore. Nevertheless, it is more than likely that “operational trials” will come first and most of them will happen in “procedural airspace” where currently no ATM-surveillance is available. Using operational trials is acknowledged as means to introduce new procedures and applications, to allow that ICAO procedures and –SARPs can be published. It is not desirable to have operational trials lasting for a prolonged period, as these trials depend heavily on the correct safety- and regulatory actions by the State or States involved. It also negates the perspective of having harmonised and standardised international procedures put in the place without delay. A good example for a possible future ASAS-use is the oceanic ITP (In-Trail Climb or Descent Procedure). It would permit that flights, constrained by conflicting traffic on the same track, would be allowed to climb/descend through the level of the procedurally conflicting traffic by using the surveillance capabilities of ASAS. The definition of an In-Trail Procedure (ITP) is:

“a procedure employed by an aircraft that desires to change its flight level to a new flight level by climbing or descending in or behind one, or between two Same Track, Potentially Blocking Aircraft which are at an Intervening Flight Level which are at less than the standard longitudinal separation minimum.”

As this procedure is most of the time used in areas and airspace with no ground surveillance available, it is determined that:

“the longitudinal separation minimum between the climbing or descending ITP Aircraft and a level Potentially Blocking Aircraft, applicable in determining the ITP criteria. The ITP Distance-Based Separation Minimum is based on the ICAO DME separation procedure and is 10 NM”.

2.10. It is expected that the operators using the future ITP-Procedure will use a Cockpit Display of Traffic Information (CDTI) to “measure” the distance to a conflicting flight, assimilating it to the Distance Measuring Equipment (DME) based separation established by ICAO. It becomes quickly evident that this will create new challenges and problems, despite the fact that the chosen approach is making a lot of sense. Fact is that it is not at all that innocent in comparing a “raw reading” of a DME- distance, or a distance from/to a fix or waypoint using Global Navigation Satellite System (GNSS) / Global Positioning System (GPS), with an airborne distance measurement between two observed and identified targets. Completely new sets of applications and procedures are needed here as not only the distance to the other target will be of importance, but also other factors must be considered as well. For instance the correct target identification or the navigational precision of the flights shown on the displays and involved in the ASAS-procedure must be considered. In particular when outages or degradations occur, such as a GPS-receiver going into Receiver Autonomous Integrity Monitoring (RAIM) or if the Navigation Uncertainty Category (NUC) – values displayed are very low. This has to be a part of the automation.

2.11. There has been a lot of discussion about the difference of a CDTI, when comparing it to a TCAS-display. Basically, both displays are looking very much the same and both are somewhere fitted on the avionics panel in a cockpit. What is currently hindering the debate about the differences between a CDTI- and a TCAS-display is the lack of agreed definitions as we are currently lacking of CDTI Minimum Operational Performance Specifications (MOPS) from ICAO or another recognized international technical organization. Whereas TCAS-displays are normally rather small and show only very basic features and they are most importantly limited to receive only “active surveillance” data. They must aid the crew to acquire visually the intruder aircraft (or aircraft in plural) that triggered an Resolution Advisory (RA) and Traffic Advisory (TA) and, generally speaking, they are helping the crew to improve and enhance its situational awareness.

CDTIs are expected to have multiple sensor and surveillance data inputs and will most probably permit a fusion of those data sources (including ADS-B, TIS-B, as well as active TCAS-tracks). This will need stringent data checking criteria before such tracks can be fused into one. This is exactly where the currently discussed hybrid TCAS MOPS will come from, by mixing active and passive surveillance. But the safety in this area must be very high. CDTIs must have, compared to the very basic TCAS-displays some additional features such as the presentation of flight intent. This could be done via “clues” (such as speed tendencies) or via “hints” that the ASAS- crew could use to follow an aircraft “in trail”, e.g. permitting to anticipate speed reductions. The CDTI must also utilise a much more sophisticated target labelling, including Flight Identification (ID; using Mode S or ADS-B). In this respect the TCAS- displays just depict the surrounding targets by showing a “blip symbol” and the relative position of the target (horizontally and vertically). But without any target labelling or positive identification shown to the crew. As mentioned above the certification of CDTIs is not yet standardized and regulated by ICAO, or any other international agency. This is a problem that needs to be solved as quickly as possible. It cannot be that every area and ASAS-region will implement, or at least to “test” its ASAS-applications by using a particular and different airborne hardware. “Compatibility” is the keyword here and it must be ascertained that clear standards and minimum requirements are published as soon as possible. This will help the airlines to deploy a harmonized ASAS-fleet that it can operate without restrictions wherever such applications are used operationally.

2.12. Some of the issues related to CDTIs are clearly Human Factor (HF) issues. The most significant seems to be the different perception caused by the relative positions during manoeuvring, compared to the situation on the ground where the relative positions are constant for any particular screen selection. In maritime surveillance such problems of a moving surveillance are referred to as “radar-assisted collisions” and there has already been an airborne example where the pilot considered that they were turning away from crossing traffic, but instead converged on the traffic (see Eurocontrol ACAS Bulletin).

Before surveillance systems can be used operationally it has to be ascertained that the operators are fully trained and qualified to use them. Another important point is that the aircraft (or aircraft pairs) on the CDTI are properly identified. ATC will transmit the identification (or call-signs) of the conflicting traffic to the air crews for conflict resolution or simply to operate their flight “reference to” a given traffic. There must be a high degree of certainty that the risk of misidentification is tolerably low. Or, using a term that is often quoted in safety management documents: the risk must be “tolerable”. As new operators (e.g. pilots) are entering the wide field of ATM- surveillance it must be ascertained that the new operational realities are correctly identified and assessed from a safety point of view.

2.13 If the ground ATC-system uses radar with Mode A and C only, then the disparity of surveillance information and, more importantly, the identification and correlation process of aircraft labels must be considered as well. If the aircraft labelling of an ATC-system is using Mode A/C as basis for identification and correlation, the correlation is passing via the Flight Data Processing System (FDPS) to achieve a positive identification. This would mean the ground system will use a different target identification process when comparing it to the airborne aircraft that is using ASAS. It will be fed by Mode-S or ADS-labels where the identification is done via the Flight ID. Another difficulty to be solved before ASAS can go into operation is the way that ATC must point out a conflicting (or restricting) traffic to a suitably equipped aircraft applying an ASAS-procedure? This must be done, at least initially, via R/T and voice as other feasible solutions such as via CPDLC or other electronic means are not yet developed and available. The problem is that the operators must have at their disposal ICAO-phraseology to permit ATC to show and transmit in a clear and unambiguous manner the call-sign and identification of the conflicting traffic to the ASAS-equipped aircraft. Furthermore, the crew must have at their disposal clear phraseology to read-back these instructions in a standard manner. The use of a call- sign of another aircraft via R/T could possibly confuse the other crew as they would hear their call-sign on the frequency, but should not reply to this call. The ICAO SCRSP (Surveillance and Conflict Resolutions Systems Panel), now renamed to ASP (Aeronautical Surveillance Panel) has identified this problem back in 2005. It has asked the OPSP (Operations Panel) to study this issue and to bring forward, if possible, some good proposals. So far nothing firm is discussed by the stakeholders, despite the fact that the operational use of the first ASAS-applications is not that distant anymore.

2.14. IFATCA Provisional Policy on ASAS/CDTI is:

“Where ASAS is implemented a clear and unambiguous statement of the separation responsibilities of pilots and controllers is required.

IFATCA has no fundamental objection to the use of CDTI in areas where it is demonstrated to maintain and improve system safety.

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

IFATCA considers the following to the minimum attributes of any CDTI system used in Airborne Separation Assurance / Assistance applications:

Positive unambiguous identification of all relevant aircraft to the standards currently required of ATC systems and controllers;
Sufficient information as to the intent of relevant aircraft to avoid any action taken in maintaining separation from generating additional conflict.”

2.15. When reading through these Provisional Policy statements, it becomes clear that they are not up-to-date anymore. Some urgent adaptations are needed. ASAS is now in a much more mature and advanced state as back in 2003, when these policies were adopted. It is therefore proposed to delete these provisional Policy statements and to substitute them by new IFATCA Policy statements. The sentence where the conditions for the responsibility for the separation provision is stated is only partially correct as, by definition, the responsibility for separation provision can only lie with the controller, but never with the crew. So, there is a need to change this accordingly. Many of the ensuing Provisional Policy statements are too much centred on cost benefit issues and are therefore not so relevant for IFATCA. Finally, it must be noted that several times the term “CDTI” is used when actually the policy is referring to ASAS-applications and so changes to the wording are required.

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Conclusions

3.1. ASAS and ADS-B are not the same systems although they are most often using the same surveillance data and – technology. ASAS can be operated without ADS-B data, for instance with TIS-B. But most of the time it will use ADS-B ES-messages, or similar alternatives such as Universal Access Transceiver (UAT) or VHF Data Link Mode 4 (VDL4) – data.

3.2. ASAS will bring in new operators who will use “ATM surveillance” operationally. This must be correctly assessed from a safety point of view. This will be for sure a big challenge for ICAO and the States’ regulators facing those new problems and new safety issues that will require mitigations.

3.3. IFATCA’s current Provisional Policy states:

“IFATCA has no fundamental objection to the use of CDTI in areas where it is demonstrated that the current system safety is maintained or even improved”.

This means that IFATCA is not at all against the use of ASAS and its applications, but the safety must be maintained and/or improved.

3.4. ASAS is no longer called a “separation assurance system” but is now a “separation assistance system”. This allows for other considerations, not just separation. This is the reason why IFATCA supports most of the views of ASAS as laid down in the ICAO ASAS circular, as well as the statements of PO ASAS. Further developments and refinements, such as the CASCADE-project in Europe must be closely followed and observed and it’s too early to make any statements about them so far.

3.5. Some of the emerging ASAS-applications, for instance ITP to name just one, are slowly entering the field of operational tests and flight validations. They will bring in many new issues that must be assessed and analysed before going operational. It is simply not the same, from a safety point of view (including for risk assessments), that a crew is transmitting a DME- or GNSS-distance reading to ATC, or an ASAS/CDTI distance measurement. Before the latter can be used safely several actions must be correctly executed beforehand by the aircrew: correct target identification, identification of the conflicting blip and also determination of the navigational precision of the targets on a CDTI.

3.6. Another problem is of how to point out another aircraft or several targets (conflicting traffic) by R/T and voice. This has been identified by several ICAO panels as a difficulty and problem. The risk is not only that the wrong target could be chosen by the crew but also that the aircraft which call-sign is used and pointed out (as Flight ID), gets confused by this use of its call-sign on an ATC-frequency. There is an urgent need that appropriate and clear standard ICAO-phraseology is created and implemented for these particular ASAS-applications.

3.7 Before ASAS-applications are used operationally, IFATCA requires that all implementations, including “trials”, are correctly assessed and analysed in regards to their safety and the risks involved. Maintaining operational trials active for a prolonged period is undesirable.

3.8. Finally, it must ascertained that only the correct terms are used for ASAS and ADS-B and no more mixes. This is essential as it will help that all stakeholders understand what happens with which surveillance technology and it will permit that all can be implemented in a safe and correct manner.

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Recommendations

It is recommended that;

4.1. IFATCA Provisional Policy on page 3 2 7 5 of the IFATCA Manual:

“Where ASAS is implemented, a clear and unambiguous statement of the separation responsibilities of pilots and controllers is required.

IFATCA has no fundamental objection to the use of CDTI in areas where it is demonstrated to maintain and improve system safety.

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

IFATCA considers the following to be the minimum attributes of any CDTI system used in Airborne Separation Assurance applications:

Positive unambiguous identification of all relevant aircraft to the standards currently required of ATC systems and controllers;

Sufficient information as to the intent of relevant aircraft to avoid any action taken in maintaining separation from generating additional conflict.”

is deleted.

4.2. IFATCA Policy is:

Where ASAS-applications are implemented, a clear and unambiguous statement for separation responsibility is required.