46TH ANNUAL CONFERENCE, Istanbul, Turkey, 16-20 April 2007WP No. 95Surveillance Applications Policy – Review Policy on ADSPresented by TOC |
Summary
Part of the 2006 “Surveillance Application Policy” work programme for the Technical and Operations Committee (TOC) included a review of IFATCA provisional Policy on ADS. This paper details the changes since the policy was last reviewed in Santiago-1999 and reports on the changes to ICAO documentation. This includes the introduction of the “Manual Air Traffic Services Datalink Applications Doc9694” and the changes to PANS ATM Doc 4444 and Annex 11. Part of the review is to consider that ADS policy may need to be retained or modified to include ADS-B and indeed any other form of ADS that may be used in the future.
Introduction
1.1 When the introduction of Automatic Dependence Surveillance (ADS) commenced, thought was never given that the term ADS may lay meaning to a generic function (or description) rather than a specific piece of technology. Initially ADS was established as a datalink (either satellite or VHF) to be used within FANS 1/A avionics to provide improved navigational reporting in areas of non-radar.
1.2 While this technology is mature and the procedures surrounding its use have been refined, the emergence of another ADS technology brought about some confusion. The initial diagnosis was that it was significantly different in both hardware and use to warrant recognising the differences between them and other generically named ADS technologies. Even though they were different, the fact remained it was automatic in the way it worked, dependant (the aircraft navigation system is responsible for the information) and was a form of surveillance.
1.3 The term ADS is now considered the methodology of surveillance not a particular technology. Changes to this terminology have been made to make a clear distinction between the two and also to allow room for any other ADS technology to be accurately developed.
1.4 What was historically known as ADS in now called ADS-C; the ‘C’ standing for contract, depicting the connection required to make use of the technology (data authority). The newest technology is ADS-B; where the ’B’ stands for broadcast, depicting that it is continuously broadcast.
1.5 ICAO through OPLINK panel has made these amendments (even though not all of these have yet been published, e.g. ICAO Manual Air Traffic Services Datalink Applications Doc 9694) to both capture ADS-B and to make distinctions between ADS-B and ADS-C.
1.6 IFATCA policy on ADS was written in reference to ADS-C and would need to be changed to reflect this. Consideration must be given though, to the fact that some of the policy may in fact be generic enough to cater for both ADS-C and ADS-B and would therefore remain as generic ‘ADS’ policy. For this review TOC has stated that this policy is referencing ADS-C.
1.7 In the last review of current provisional policy (Santiago 99 WP 94), mention of the forthcoming amendments to ICAO PANS-ATM Doc 4444 noted that most of the current IFATCA policy may indeed become redundant. This paper, while looking at what changes were made to ICAO PANS-ATM Doc 4444 and indeed incorporating ICAO Manual Air Traffic Services Datalink Applications Doc 9694 will attempt to establish any reinstatement of ICAO requirements in IFATCA policy. Consideration must also be given to new ADS technology’s (ADS-B) and if current policy indeed would pertain to both (and any other ADS related technology, yet to be introduced).
1.8 In the following pages, bolded italics represent IFATCA Policy and any normal italic is reference to other material as required to provide argument and support to the points presented.
Discussion
2.1 IFATCA Policy
2.1.1 IFATCA has Provisional Policy on ADS. This Provisional Policy was originally written in reference to what we now know as “ADS-C”. Editorial amendments may be necessary and will be detailed in this discussion.
2.1.2 As the Policy contains multiple statements we will break these up into their relevant paragraphs and address each of these as required.
2.2 IFATCA Provisional Policy is:
| “Before an ADS service is introduced into operational service, the necessary system components to provide a control service and to support the control task shall be in place.
Only pertinent and useful flight data should be supplied to the control team, which supports and enhances the building of human mental models and controller situation awareness.” |
2.2.1 This Provisional Policy statement was accepted prior to all of the relevant ADS-C ICAO documentation being produced. ICAO Manual of Air Traffic Services Datalink Applications Doc 9694 (from now on referred to as Doc 9694) has been published in 1999 and contains intimate detail on how to design and implement an ADS-C service. ICAO ANS ATM Doc 4444 (from now on referred to as Doc 4444) also provides information on the required functional requirements.
2.2.2 These include all the necessary hardware/interface components and the human factors issues required with managing this interface.
2.2.3 In Doc 9694 Chapter 5 it discusses “ADS high level operational requirements”. These provide the concepts of how an ADS-C service must function.
In Doc 4444 it also states the functionality required:
“13.2.3
Several significant functional requirements are necessary to permit the effective implementation of an ADS service in a CNS/ATM environment. Ground systems shall provide for:
a) the transmitting, receiving, processing and displaying of ADS messages related to flights equipped for and operating within environments where ADS services are being provided;
b) the display of safety-related alerts and warnings;
c) position monitoring (the aircraft’s current position as derived from ADS reports is displayed to the controller for air traffic situation monitoring);
d) conformance monitoring (the ADS reported current position or projected profile is compared to the expected aircraft position, which is based on the current flight plan. Along track, lateral and vertical deviations that exceed a pre-defined tolerance limit will permit an out-of-conformance alert to be issued to the controller);
e) flight plan update (e.g. longitudinal variations that exceed pre-defined tolerance limits will be used to adjust expected arrival times at subsequent fixes);
f) intent validation (intent data contained in ADS reports, such as extended projected profile, are compared with the current clearance and discrepancies are identified);
g) conflict detection (the ADS data can be used by the ADS ground system automation to identify violations of separation minima);
h) conflict prediction (the ADS position data can be used by the ADS ground system automation to identify potential violations of separation minima);
i) tracking (the tracking function is intended to extrapolate the current position of the aircraft based on ADS reports);
j) wind estimation (ADS reports containing wind data may be used to update wind forecasts and hence expected arrival times at waypoints); and
k) flight management (ADS reports may assist automation in generating optimum conflict-free clearances to support possible fuel-saving techniques, such as cruise climbs, requested by the operators).
Note.— The use of ADS does not relieve the controller of the obligation to continuously monitor the traffic situation.”
2.2.4 While technically, certain requirements must be met, the interface with this technology is also important. Doc 9694 details the ‘human factors’ required to introduce this technology. It stresses the importance of a ‘human centred’ approach to design and provides the arguments as to why this is fundamental for the long term success of ADS-C.
The following extract details the required approach:
“6. HUMAN FACTORS ISSUES RELATED TO DATA LINK APPLICATIONS
6.1
[…] General Human Factor’s issues, to be considered with the guidance material listed in the reference section of this appendix, include:a) the level of safety targeted for the future system should be defined not only with reference to various system statistics, but also with reference to error-inducing mechanisms related to human capabilities and limitations, as well as individual cases;
b) the definition of system and resource capacity should include reference to the responsibilities, capabilities and limitations of ATS personnel and pilots, who must retain situational awareness in order to discharge their responsibilities as indicated in the principles of human-centred automation;
c) the provision of large volumes of information to users should be limited to what is absolutely necessary, and should be mediated by methods that effectively package and manage such information to prevent information overload, while providing pertinent information to particular operational needs;
d) the responsibilities of pilots, air traffic controllers and system designers should be clearly defined prior to the implementation of new automated systems and tools;
e) services and procedures should be provided to ensure the preservation of situational awareness for both data link and non-data link equipped aircraft and ground facilities;
f) when operating a data link system, there should be no increase in head-down time that would adversely affect safe operation;
g) voice communication to supplement data link system operation should be available; and
h) maximum use of data link should not impose undue competition for display or control resources.”
2.2.5 Surmising the content of both Doc 9694 and Doc 4444 we have detailed direction of the required ‘system components’ which include the human interface and making sure both systems and procedures support the controller to function with ADS-C safely. While this ICAO documentation covers ADS-C significantly, the policy will still be relevant as generic ADS policy due to other emerging ADS technologies. Even though some documentation on ADS-B (for example) is available to assist in the design and implementation of such systems, the work is conceptual and certainly immature by standard comparing it to the information available on ADS-C.
2.2.6 It is recommended that this IFATCA Provisional Policy statement on ADS is retained.
2.3 IFATCA Provisional Policy is:
| “An ADS system must be validated so that it meets the appropriate ICAO safety and certification standards.” |
2.3.1 Do we really need to define a statement that applies to all ATS systems not just to ADS-C? The necessary requirements for an ADS-C system to be validated and to operate safely are well contained in Doc 4444/ 9694.
2.3.2 Safety issues with design and implementation of any new procedure and technology are well covered in Annex 11:
“2.26 Safety management
2.26.5 Any significant safety-related change to the ATS system, including the implementation of a reduced separation minimum or a new procedure, shall only be effected after a safety assessment has demonstrated that an acceptable level of safety will be met and users have been consulted. When appropriate, the responsible authority shall ensure that adequate provision is made for post-implementation monitoring to verify that the defined level of safety continues to be met.”
2.3.3 The application of the safety requirements are further detailed in Chapter 2 ‘ATS Safety Management’ of Doc 4444 and the ICAO Safety Management Manual Doc 9859.
2.3.4 It is recommended that this IFATCA Provisional Policy statement on ADS is deleted.
2.4 IFATCA Provisional Policy is:
| “When entering ADS airspace where an ADS-ATC service is provided existing HF and/or VHF voice communications shall be established to confirm their serviceability.” |
2.4.1 In the concerns raised from Jerusalem 1995 – WP 101, an argument was given that the future of ADS-C operations would give reason to removing existing VHF/HF communications. While this hasn’t been the case (in fact upgrades to existing HF systems have continued), one could argue that this may be due to the slow uptake of FANS 1/A avionics.
However, Doc 9694 states the following:
Chapter 6 ‘Human Factors issues related to Datalink Applications’:
“g) voice communication to supplement data link system operation should be available;”
2.4.2 In chapter 3 ‘Datalink Applications’ under the heading of ‘Air-ground and ground- ground data link communications’ it states:
“3.9 The required air-ground data link will be ATN compatible for most applications and could be either satellite data link, VHF digital data link, Mode S data link, or any other medium which meets the operational requirements. The ATC and aircraft systems will select the most suitable path based on time-varying considerations such as geographical location, cost, delay, throughput and link availability. For example, in oceanic airspace, satellite data links will most likely be used, while in domestic airspace VHF or Mode S could be used.
3.10 The resulting communications links will appear seamless from the user’s perspective (i.e. independent of the communications systems in use).
3.11 Voice communication will be available to complement data link system operation.”
2.4.3 Again in Chapter 3 under the heading of ‘Operational requirements’ it states:
“3.24 A data link based ATS must include the capability of exchanging messages between the pilot and the controller. A direct voice communication capability should be available for at least emergency and non-routine, safety-related communications. In order to cater for emergency situations, the system will provide for a pilot- (or, exceptionally, system-) initiated ADS emergency mode, which would indicate the state of emergency, and include an ADS report.”
2.4.4 In Doc 4444 it also details the relevant requirements for the use of controller-pilot communications and having the necessary back-up systems:
“13.4.3.3 COMMUNICATIONS
Controller-pilot communications shall be such that the possibility of communications failure or significant degradations is very remote. Adequate back-up facilities shall be provided.”
2.4.5 It is recommended that this IFATCA Provisional Policy statement on ADS is deleted.
2.5 IFATCA Provisional Policy is:
| “Separation standards for use with ADS shall be global standards, and applied globally.” |
2.5.1 In WP94 – Santiago 1999, it was discussed that ADS/RNP standards were being developed. They have now been developed and included in Doc 4444; the details located in Chapter 5 paragraph 5.4.2.6.4.
2.5.2 ICAO is also working on publishing the required standards for ADS-B; evidence so far is showing us that the process will take some time (proposed Nov 2007) and that local regulator approval will be (and has) been sought initially to use these new technologies.
The argument that all ADS standards need to be global would apply to all ATM systems; whether it be a Safety Management System or using 3 NM in a surveillance environment. It is possible, that regional variances will exist in application of ADS-C standards (and other standards/practices). Trials eventuating in acceptable, non- global standards will always (and do) exist.
2.5.3 It is recommended that this IFATCA Provisional Policy on ADS is deleted.
2.6 IFATCA Provisional Policy is:
| “The separation standards to be applied between radar targets and ADS positions must be subjected to an ICAO approved collision risk analysis.” |
2.6.1 Doc 4444 states:
“13.5.3.3 Distance-based separation minima for use with ADS may be applied between ADS-derived aircraft positions, or between ADS-derived positions and radar-derived positions. The positions of the aircraft shall be extrapolated or interpolated, as necessary, to ensure that they represent the positions of the aircraft at a common time.
Note 2.— Information on the determination and application of separation minima is contained in the Manual on Airspace Planning Methodology for the Determination of Separation Minima (Doc 9689).”
2.6.2 Is it just “radar targets” or do we need to specify all surveillance types? With the introduction of ADS-B surveillance and the future prospects of multilateration, we will need to be more generic in terminology.
2.6.3 In the ICAO ‘Manual of Airspace Planning and Methodology for the Determination of Separation Minima’ Doc 9689, it states:
“1.11 The introduction of ADS into the procedural ATC environment offers the potential for more frequent position updates as well as information on the future intent of the aircraft. In an ADS environment where position reports are communicated directly from the aircraft to ATC, and where ATC is automatically kept up to date on the intentions of the aircraft, significant reductions in separation minima should be possible. The extent of separation reductions need to be determined by either collision risk modelling or the other techniques detailed in the methodology in this manual.”
In Appendix 8, it provides an example of this collision risk model for determining lateral separation minima for ADS-based air traffic control.
2.6.4 Again, while there are many examples of ADS-C standards, established through correct collision risk analysis, the future of ADS-B and its use both as a stand alone surveillance and used in other forms (e.g. multilateration) provide further emphasis for this policy. While SASP has produced a comparative assessment with ADS-B and radar (5 NM) and is working on one for a 3 NM standard, local regulator approved standards will exist and emphasis on the accuracy of their conclusions needs for sound policy.
2.6.5 It is recommended that the IFATCA Provisional Policy on ADS is amended as below and accepted as IFATCA Policy:
“The separation standards to be applied between all surveillance targets and ADS positions must be subject to an ICAO approved collision risk analysis.”
2.7 IFATCA Provisional Policy is:
| “The number of different separation standards available for use should be kept to a minimum. ATC should have the option to limit the number of separation standards in use at any time.” |
2.7.1 Will this be possible? Should we actually be more concerned about how and when different standards are used/trained/managed? Does IFATCA want to limit the possibility of further advancements to technology that will allow an ATCO to manage a multitude of standards with additional tools to monitor them? Flight Plan Conflict functions may allow different standards to be monitored with little complexity. What about further RNP requirements, won’t improvements to navigation allow less restrictive standards and therefore produce more efficient trajectories? Like all updated technology, being ‘backwards compatible’ and allowing for the less capable avionics will always be required. So the complexity will remain, older well established separation standards will always be required.
2.7.2 Do ATC currently have the ability to limit the number of separation standards in use? Everyday we see opportunity to use vertical separation vs lateral vs visual separation and that is just in the radar environment alone. Professional ATC will always work within their skill set applicable to their workload and perhaps this statement should apply to all new technologies (consider ADS-B also).
2.7.3 The following is extracted from the previous review of this policy paragraph conducted in Santiago 1999 – WP 94:
“From a technical standpoint IFATCA should not close its mind to the probability that future ATC automation systems may well assist the controller in applying a wide variety of separations according to the various CNS parameters pertaining in particular situations. The need to limit the number of standards in use may then only arise when the ATC automation system is operating in a degraded mode.
Note: A degraded mode is considered to be the operation of ATC using redundant (back-up) systems. This is when ‘normal systems’ no longer exist, as they have been subject to failure(s).”
2.7.4 The argument here needs to be that the ‘required support’ to manage all the possible standards should be in place (see next paragraph), prior to the introduction of multiple standards based on complex CNS requirements. This may also be contained in IFATCA policy on Automation/Human Factors.
2.7.5 It is recommended that the IFATCA Provisional Policy statement above on ADS is deleted.
2.8 IFATCA Provisional Policy is:
| “ATC will require the provision of assistance tools for managing airspace where multiple separation standards apply.” |
2.8.1 In Santiago 1999 – WP 94 it stated that the forthcoming amendments to Doc 4444 would address these issues; the current paragraph from Doc 4444 states:
“13.2.3
Several significant functional requirements are necessary to permit the effective implementation of an ADS service in a CNS/ATM environment. Ground systems shall provide for:
a) the transmitting, receiving, processing and displaying of ADS messages related to flights equipped for and operating within environments where ADS services are being provided;
b) the display of safety-related alerts and warnings;
c) position monitoring (the aircraft’s current position as derived from ADS reports is displayed to the controller for air traffic situation monitoring);
d) conformance monitoring (the ADS reported current position or projected profile is compared to the expected aircraft position, which is based on the current flight plan. Along track, lateral and vertical deviations that exceed a pre-defined tolerance limit will permit an out-of-conformance alert to be issued to the controller);
e) flight plan update (e.g. longitudinal variations that exceed pre-defined tolerance limits will be used to adjust expected arrival times at subsequent fixes);
f) intent validation (intent data contained in ADS reports, such as extended projected profile, are compared with the current clearance and discrepancies are identified);
g) conflict detection (the ADS data can be used by the ADS ground system automation to identify violations of separation minima);
h) conflict prediction (the ADS position data can be used by the ADS ground system automation to identify potential violations of separation minima);
i) tracking (the tracking function is intended to extrapolate the current position of the aircraft based on ADS reports);
j) wind estimation (ADS reports containing wind data may be used to update wind forecasts and hence expected arrival times at waypoints); and
k) flight management (ADS reports may assist automation in generating optimum conflict-free clearances to support possible fuel-saving techniques, such as cruise climbs, requested by the operators).
Note.— The use of ADS does not relieve the controller of the obligation to continuously monitor the traffic situation.”
2.8.2 While this provides the basis for an ADS (presumable ‘C’) system to provide correct automation and possible conflict detection/prediction; can we safely assume that this will provide protection and equip controllers to manage all ADS surveillance complexities that currently and will exist as ADS technology evolves?
2.8.3 It is recommended that the IFATCA Provisional Policy above on ADS is accepted unchanged as IFATCA Policy.
2.9 IFATCA Provisional Policy is:
| “The ADS system shall provide a warning to pilot and controller whenever navigation accuracy is degraded below that required to operate in the airspace, and that this will affect separation standards. Procedures must be in place to restore any loss of separation in a timely manner.” |
2.9.1 The Figure of Merit (included in basic ADS-C report) is a report detailing any change to the position accuracy and is included in all ADS reports.
It is defined in Doc 9694 as:
“FOM.
Indicates the figure of merit of the current ADS data. The information consists of the position accuracy and indications 1) whether or not multiple navigational units are operating, and 2) whether or not ACAS is available.”
It goes into further detail:
“Figure of merit (FOM) field change
3.58 The FOM field change event is triggered by change in the navigational accuracy, navigational system redundancy or in the airborne collision avoidance system (ACAS) availability.
3.59 The ADS report resulting from a FOM field change event is sent once each time the event occurs.
3.60 An ADS report sent as a result of the occurrence of a FOM field change event contains only basic ADS information.”
2.9.2 Some ATC systems will reject reports that fail to meet certain criteria, or apply a formula to the data received to determine its ability to be displayed. An example of this is the Australia Eurocat system that will use a different symbol to display low- quality ADS reports.
2.9.3 ATC systems also use conformance monitoring, both in the present (the expected position against the actual reported position and the aircrafts flight level) and future monitoring (next position report and next +1) to alarm the controller of avionic reported errors.
Doc 4444 Paragraph 13.4.3.4.4 states:
“An ATC unit providing an ADS service to an aircraft, shall check the ADS three- dimensional position information received from that aircraft through pilot reports and/or flight plan conformance.”
2.9.4 What the ADS-C system doesn’t detect is the navigation system producing false data (reporting over a known position even though the aircraft isn’t over the position). This is also applicable in all non-radar environments; if an aircraft’s navigation system reports over a position and the navigation system is incorrect, the controller receiving the position report will not be able to detect this. An important point is remembering the collaboration between ADS-C and the required navigation performance (RNP 10 or RNP 4 etc); covered by additional ICAO documentation (Doc 9613).
2.9.5 Once again this needs to be considered for all ADS applications and while the argument may support its deletion based solely on ADS-C, with other ADS technologies being developed is relevant. In particular is the need to include the ‘integrity’ of ADS data. While the navigation system may meet the required accuracy does it meet the ‘integrity’ component essential for use in a ‘radar-like’ ADS-B system?
2.9.6 It is recommended that the IFATCA Provisional Policy on ADS is amended as below and accepted as IFATCA Policy:
“The ADS system shall provide a warning to pilot and controller whenever navigation accuracy and/or integrity is degraded below that required to operate in the airspace, and that this will affect separation standards. Procedures must be in place to restore any loss of separation in a timely manner.”
2.10 IFATCA Provisional Policy is:
| “Aeronautical telecommunications services provided by third party service providers and used in ADS operations must meet the appropriate standards of a safety critical system.” |
2.10.1 Annex 10 Part 3 states:
“3.3.4 Recommendation.— Civil aviation authorities should co-ordinate, with national authorities and aeronautical industry, those implementation aspects of the ATN which will permit its world-wide safety, interoperability and efficient use, as appropriate.”
2.10.2 The ICAO Manual of Technical Provisions for the Aeronautical Telecommunication Network (ATN), Third Edition, 2002. (Doc 9705) has intimate details of these requirements.
2.10.3 It is recommended that the IFATCA Provisional Policy statement above on ADS is deleted.
2.11 IFATCA Provisional Policy is:
| “ADS reporting rates should be determined by the ATS operational requirement.” |
2.11.1 Doc 4444 states:
“13.4.3.4.1.4 The contract may include the provision of basic ADS reports at a periodic interval defined by the ADS ground system with, optionally, additional data containing specific information, which may or may not be sent with each periodic report. The agreement may also provide for ADS reports at geographically defined points such as waypoints, in addition to other specific event-driven reports.”
2.11.2 It is recommended that the IFATCA Provisional Policy statement above on ADS is deleted.
2.12 IFATCA Provisional Policy is:
| “Procedures for the provision of an ADS service shall not impose any restriction upon the controller on requesting reports from aircraft.” |
2.12.1 Doc 4444 states:
“13.4.3.4.3.1 Initial ADS agreements shall be determined by the ATS authority. Subsequent modifications to individual contracts may be made at the discretion of the controller based on the prevailing traffic conditions and airspace complexity.”
2.12.2 It is recommended that the IFATCA Provisional Policy statement above on ADS is deleted.
2.13 IFATCA Provisional Policy is:
| “Displays of ADS information that are presented to the controller should be designed so that they meet the need of the control task and enhance the usability of the system.
ADS system design must seek to optimise the interface at the controller workstation. Control of traffic using position data derived from ADS and radar surveillance can only be used where the control system supports both types of surveillance. Whenever a controller interface derives data from a combination of surveillance systems, the source and derivation of position data in use must be clearly and continuously evident to the controller.” |
2.13.1 Doc 9694 chapter 3 ‘Controller Interface’ states:
“3.18 The controller interface will contain the required tools for the composition of air- ground data link messages. ATS providers will define and develop specific controller interfaces tailored to their particular needs. The human-machine interface will be left to the individual service provider. The controller interface should be efficient, easy to operate and provide a rapid message input mechanism. The interface should also provide a means to display air-ground messages.”
2.13.2 Doc 4444 states:
“13.4.2 Presentation of ADS data
13.4.2.1 Appropriate ADS data shall be presented to the controller in a manner suitable to achieve the control functions in 13.4.1.4. Display systems shall incorporate a situation (plan view) display, textual information display, aural and visual alerts in such combinations as deemed appropriate.
13.4.2.2 Display systems may display actual ADS report information only or a combination of actual ADS report information and data derived from ADS reports. Additionally, display systems may incorporate surveillance information from a number of other sources, including data derived from radar, the flight data processing system (FDPS) and/or voice position reports.
13.4.2.2.1 Where surveillance information is derived from different sources, the type of surveillance shall be readily apparent to the controller.
13.4.2.3 ADS information available to the controller on a situation display shall, as a minimum, include ADS position indications and map information.
13.4.2.3.1 When applicable, distinct symbols should be used for presentation of such items as:
a) ADS position;
b) combined ADS/SSR position;
c) combined ADS/PSR position;
d) combined ADS/SSR/PSR position; or
e) predicted positions for a non-updated track.
13.4.2.3.3 Label information shall, as a minimum, include aircraft identification and level information. All label information shall be presented in a clear and concise manner. Labels shall be associated with their ADS position indications in a manner precluding erroneous identification.
13.4.2.5 Safety-related alerts and warnings, including emergency/urgent reports, shall be presented in a clear and distinct manner. Provisions shall be made for alerting the controller when expected ADS reports are not received within an appropriate time.”
2.13.3 Again, in support of ADS-C design and application there is sufficient enough mature documentation to conclude deletion. But if we consider ADS-B in its infancy, do we need these same arguments to apply? Multiple surveillance data sources will become the norm, and its clarity must be continuously evident to the controller. In the working paper ‘Surveillance Applications Policy – Operational Applications of ADS-B’, Agenda item B.5.12 for Istanbul 2007, TOC have concluded that the complexity of symbology, appropriate interfaces and positive ‘human centred’ design principles need to apply.
2.13.4 It is recommended that the IFATCA Provisional Policy above on ADS is accepted unchanged as IFATCA Policy.
2.14 IFATCA Provisional Policy is:
| “Global standards and procedures must address requirements of what independent verification of position data is required before dependent position data is used for separation.
To ensure integrity of system surveillance data (not just ATC surveillance) it is essential that the automatic transmission of erroneous dependent position data can be disabled or marked as inaccurate during all stages of flight.” |
2.14.1 Hong Kong 2004 – WP 102 raises questions that are still yet to be fully addressed. The concerns as to the accuracy and integrity of the data received in dependant surveillance reports is crucial for ATC to rely on this information.
2.14.2 Again in the working paper (item B.5.12) for Istanbul 2007, TOC addresses the issues of ADS-B data using Navigational Uncertainty Category (NUC) derived from Horizontal Protection Limit (HPL) as an accurate assessment of the integrity of ADS- B data. While the use of Horizontal Figure of Merit (HFOM) may be appropriate if other measures are included, alone it is not a guarantee of this. This has been reflected in the Radio Technical Commission for Aeronautics (RTCA) producing an updated standard (DO260A) that requires avionics to produce NUC from HPL (even though avionics meeting these standards aren’t in use yet).
2.14.3 Within ADS-C reports we have the FOM sent (as addressed earlier) to establish the ‘quality’ of the ADS report. In this ADS-C system (due to the distance between aircraft and the standards being used) minor discrepancies are acceptable and the time to confirm and fix these issues have been established with accurate ‘collision risk modelling’. The possibility of 3 NM being used has placed enormous emphasis on the accuracy and integrity of ADS-B data, hence the high profile of issues such as NUC and Receiver Autonomous Monitoring (RAIM).
2.14.4 With ADS-C technology being refined over the last few years we have seen a robust approach to managing these issues. Doc 9694 details these issues with requirements for aircraft to self-monitor and automatically report significant flight variance and for the ground system to be able to confirm that the aircraft’s projected profile coincides with that stored in the ground system.
2.14.5 Again in the working paper (agenda item B.5.12) on ADS-B, TOC discusses the issues of capability to ‘switch off’ incorrect ADS-B data. This is an essential part of the protection required when using this technology. In trials conducted in Australia, incorrect Flight ID input is relatively common and with some avionics, the ability to change it ‘airborne’ is limited. This issue alone (without discussing incorrect data being sent) is serious enough to warrant this option as standard. This has been recognised in Australia with the proposed changes to ‘Civil Aviation Regulations’ mandating this function.
2.14.6 It is recommended that the IFATCA Provisional Policy above on ADS is accepted unchanged as IFATCA Policy.
Conclusions
3.1 The term ADS while generic in definition had been used to define a certain category of surveillance (ADS-C). While this technology still exists, another technology using ‘automatic dependant surveillance’ has been developed (ADS-B). To limit confusion changes have been made to ICAO documentation to reflect these differences and will be proposed (if required) for change in current IFATCA provisional policy. Not withstanding though, the possibility that current provisional ADS policy may still be relevant for both technologies.
3.2 Much of the current provisional policy was accepted before the required changes to ICAO Air Traffic Services Annex 11, Doc 4444 and the producing of Doc 9694. Some of the policy is now in line with current ICAO documents and will need deleting/or amending.
Recommendations
It is recommended that;
4.1 IFATCA Policy on page 3213:
An ADS system must be validated so that it meets the appropriate ICAO safety and certification standards.
When entering ADS airspace where an ADS-ATC service is provided existing HF and/or VHF voice communications shall be established to confirm their serviceability.
Separation standards for use with ADS shall be global standards, and applied globally.
is deleted.
4.2 IFATCA Policy on page 3213:
The separation standards to be applied between radar targets and ADS positions must be subjected to an ICAO approved collision risk analysis.
is amended to read:
The separation standards to be applied between all surveillance targets and ADS positions must be subjected to an ICAO approved collision risk analysis.
4.3 IFATCA Policy on page 3213:
The number of different separation standards available for use should be kept to a minimum. ATC should have the option to limit the number of separation standards in use at any time.
is deleted.
4.4 IFATCA Policy on page 3213:
The ADS system shall provide a warning to pilot and controller whenever navigation accuracy is degraded below that required to operate in the airspace, and that this will affect separation standards. Procedures must be in place to restore any loss of separation in a timely manner.
is amended to read:
The ADS system shall provide a warning to pilot and controller whenever navigation accuracy or integrity is degraded below that required to operate in the airspace, and that this will affect separation standards. Procedures must be in place to restore any loss of separation in a timely manner.
4.5 IFATCA Policy on page 3214:
Aeronautical telecommunications services provided by third party service providers and used in ADS operations must meet the appropriate standards of a safety critical system.
ADS reporting rates should be determined by the ATS operational requirement.
Procedures for the provision of an ADS service shall not impose any restriction upon the controller on requesting reports from aircraft.
is deleted.
References
PANS ATM Doc 4444.
Annex 11 – Air Traffic Services.
Annex 10 – Aeronautical Telecommunications.
Manual Air Traffic Services Datalink Applications Doc 9694.
Safety Management Manual Doc 9859.
Manual of Airspace Planning and Methodology for the Determination of Separation Minima Doc 9689.
IFATCA Technical and Professional Policy Manual.
Last Update: September 29, 2020