CAP 670 Air Traffic Services Safety Requirements External ...

Safety Regulation Group Aerodrome and Air Traffic Standards

CAP 670 Air Traffic Services Safety Requirements External Consultation – 19 November 2012 to 11 January 2013 Comment Response Document This document contains AATSD response to all comments received in respect of the CAP 670 Amendment 13 consultation, which ran from 19 November 2012 to 11 January 2013. Please see CAA Information Notice IN-2013-043 for further information regarding this amendment (available at www.caa.co.uk/IN2013043).

Comments were received from:

Aeronautical and General Instruments Ltd. Tailor Made Systems Ltd. NATS Heathrow Airport Ltd.

The CAA thanks contributors for their comments and for the care and attention that they afforded to this consultation.

No. Section/Paragraph Comment Response

1 Part C, Section 2, NAV 01, paragraph 4.3

This change raises no operational issues for users of our AGIVIS IRVR systems. As a general principle, we feel it is correct that the de-rating factor should be increased for those aerodromes that can demonstrate the actual on-going performance of their runway lighting.

The CAA welcomes this positive response.


This clarification seems sensible. The CAA welcomes this positive response.


Again, this clarification seems sensible. The CAA welcomes this positive response.

http://www.caa.co.uk/IN2013043�

CAP 670 Air Traffic Services Safety Requirements External Consultation – 19 November 2012 to 11 January 2013 Comment Response Document

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We agree with the proposed changes, in that specifically making allowance for possible multiple-BLM IRVR systems should enable the assessment of more representative RVR values. For AGI specifically, changing to a multiple-BLM IRVR system would require design changes and substantial field trials.

The CAA appreciates the fact that the current generation of IRVR systems were not designed to accept inputs from multiple BLM sensors but the CAA welcomes the fact that a major manufacturer has accepted this part of our proposals and we look forward to working with that company in any field trials which they might instigate as part of their on-going product development.

5 Part C, Section 2, NAV 01

Current regulation concerning IRVR calculation was developed prior to the adoption of contemporary inspection and maintenance methods such as Photometric testing. Historically visual inspection of airfield lighting was established practice. However following a ‘successful’ CAA flight test at a major UK airport a photometric test was conducted which identified the average intensity to be in the region of 5%. It was for reasons such as this that the ICAO recommended maximum of 80% was reduced to 20% of peak beam intensity i.e. approximately 30% of the averaged beam intensity of the specified inner ellipse for the runway edge lights per CAP 168; within CAP 670.

XXXXX has been involved with airfield lighting since 1991 when commissioned by the UK Civil Aviation Authority, Ministry of Defence and DERA (Defence Evaluation and Research Agency) to study the performance of airfield lighting systems. The MALMS (Mobile Airfield Light Monitoring System) has been developed using the knowledge and experience gained in the UK research program and subsequent unrivalled experience of measuring and monitoring AGL performance around the world. Experience has shown that airports that do not use photometric testing as part of a preventative maintenance strategy for their AGL rarely if ever achieve serviceable lighting conforming to ICAO requirements for low visibility operation.

XXXXX the Founder and former owner of XXXXX originally proposed the possibility of amending the AGL light intensity values used in instrument RVR equipment in order to enable the CAA to grant “RVR Credits” and so reward aerodromes that have invested in the equipment and processes required to routinely achieve (or exceed) ICAO/CAP 168 compliant levels of serviceability.

Clearly the primary issue is one of safety which is why the CAA impose a significant ‘safety margin’ to compensate for the assumed value of light intensity inherent in the RVR calculation. Currently there

The CAA is familiar with the origins of our existing requirements but these proposals are intended to reflect and reward those airports which adopt modern maintenance practices.

The CAA is also aware that several States have adopted the ICAO recommendations (contained in Doc. 9328) in full, and for both edge and centre-line lights. The CAA proposal to raise our requirement from 20% of peak intensity to 40% of averaged intensity is therefore modest but the CAA does agree with the suggestion that we should use “the averaged beam intensity of the specified inner ellipse” because these are defined in CAP 168.

The CAA additionally agrees with the suggestion to link the increase to measured and recorded evidence of the in-service performance of runway-edge lights since presently only these fittings are specified in NAV 01.

The CAA does however wish to point out that paragraph 11.4.2 in CAP 168 refers to AGL Fault Conditions and in particular to aerodromes which support landings in ILS Cat II and III conditions. We would therefore expect these aerodromes to employ a strict inspection and maintenance regime.

The final text to be published by the CAA in paragraph 4.3 and the accompanying NOTES will therefore read as shown below: 4.3 For existing systems, IRVR values calculated using 40 per cent of

the averaged beam intensity of the specified inner ellipse for runway edge lights (as defined in Appendix 6A of CAP 168, “Aeronautical Ground Lighting Characteristics”) will be permitted following the submission to the CAA of results obtained by either photometric measurement or following the “block replacement” of those lights.


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is an 80% reduction in rated output for runway edge lights required by CAP 670, section NAV 01. We believe this could be reduced at airports that operate an effective maintenance regime. That said we believe it would be unwise to apply an across the board default minimum setting of 40% of selected runway edge lighting. This is based on our experience of testing and the minimalist approach of some airports to AGL maintenance.

We therefore believe an evidence based approach for all approved increases to the IRVR light intensity setting to be appropriate. This should comprise 2 elements:

1. Copies of results obtained from photometric inspection of the runway edge to demonstrate an average light intensity in excess of the requested uplift and;

2. Copies of photometric test results demonstrating serviceability of all runway services. Per CAP 168 11.4.2 “Unserviceable light fittings should not be permitted to alter the basic pattern of an AGL system, which should always give adequate guidance. For AGL in use in RVR less than 400 m, no two adjacent light fittings should be unserviceable.”

Regarding frequency of test results CAP 168 section 12.1.6 states “The performance of lights can change rapidly, especially at large aerodromes with high movement rates. Therefore, it is important to assess performance accurately on a regular basis and act upon the information collected. The frequency with which such assessments should be undertaken is dependent upon the type and age of the installation, maintenance policy adopted, movement rates and prevailing weather conditions. Typically, a weekly survey, with associated maintenance, has been found to be adequate for a major aerodrome.”

It is with these points in mind that I put forward the following change to Part C, Section 2, 4.3 for your earnest consideration:

Part C, Section 2

4.3 For calculating the IRVR value, 30 per cent of the averaged beam intensity of the specified inner ellipse for the runway edge lights per

NOTES:

1. For new and existing systems, the initial de-rating factor of 40% is based upon the minimum serviceability requirements set out in Chapter 6 of CAP 168 (Licensing of Aerodromes) and continuing operation at this level will depend upon satisfactory evidence of on-going inspection and subsequent maintenance programme being presented to the CAA.

2. CAA staff will determine whether continued operation at the initial de-rating factor is justified or whether the de-rating factor can be increased upward toward the ICAO recommended maximum of 80% (Doc 9328 Chapter 6.5, “Light and Light Intensity”).

3. The number of inspections required in each calendar year will depend upon the nature and frequency of aircraft operations from that aerodrome but a minimum of 4 photometric inspections (one in each quarter) should be taken during each 12 month period and the results submitted to the appropriate CAA regional office.


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CAP 168 Appendix 6A Aeronautical Ground Lighting Characteristics, shall be assumed.

NOTE: ANSPs are however encouraged to submit copies of results obtained from photometric inspection of their runway edge lighting system to the appropriate CAA regional office. The relevant staff will then assess whether the de-rating factor can be adjusted upward toward the ICAO recommended maximum of 80% (Doc 9328 Chapter 6.5, “Light and Light Intensity”) but continuing operation at this level will depend upon satisfactory evidence of on-going inspection and subsequent maintenance being presented by that ANSP to the CAA. The frequency with which such assessments should be undertaken is dependent upon the type and age of the installation, maintenance policy adopted, movement rates and prevailing weather conditions. Typically, a weekly survey, with associated maintenance, has been found to be adequate for a major aerodrome with a minimum of 4 photometric inspections (one in each quarter) taken during the previous 12 months for an aerodrome with elevated edge runway lighting. These test results will then be used to confirm the continued serviceability of the runway edge lights and average luminous intensity recorded during each inspection.

6 General Comment If I may make a general comment, there is a slight concern with what appears to be a trend towards generalisation, which requires the service provider to justify their decisions rather than complying with a prescribed set of conditions, and a general lack of detail explaining the rationale and thought process behind each of the changes. Whilst we recognise that is the Regulators prerogative to retain that information it does make it harder for us to ascertain and assess the proposed changes.

As regards the reference to ‘generalisation’, it is presumed this means less prescription. Less prescription is still the aim of risk-based regulation whereby the service provider is allowed maximum freedom to meet requirements. This will logically result in service providers having to justify their decisions, which is a correct approach in terms of SMS.

However, we do have another approach, predominantly at EU Level which tends to define requirements in prescriptive terms. This may be more to do with standardisation than safety.

This presents a challenge to all stakeholders in making the various regulatory approaches operate together.

It is hoped that any regulatory changes that are driven predominantly by detailed technical changes in, for example CAP 670 Technical Sections, are clearly justified. If not, then it is hoped the various


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comments in respect of such changes are adequately answered. For EU Level regulatory changes, for example driven by the Commission and EASA, then we are all dependant on these Agencies providing adequate rationale for such changes.

7 Part A Paragraph 6.7.1

The original text read

“The mechanism for the regulation of ATC units at aerodromes and En-Route and Terminal Control Centres is the granting of ANO Article 169 approval (and, where necessary, ANO Article 205 and 206 approvals). This mechanism is subject to Certification and Designation processes in respect of SES EU Regulations and the status of Article 169 approvals will be indicated to industry as the legislation is changed.”

But the new text reads:

“The mechanism for the regulation of ATC units at aerodromes and En-Route and Terminal Control Centres is subject to Certification and Designation processes in respect of EU Regulations.”

The new text either implies that the Oceanic Service is subject to EU rules or outside the scope of CAP 670, and we know from conversations that SRG believe neither of those statements to be correct.

No specific connection with Oceanic is implied by this change. It is meant to reflect the removal from Article 169 of the need to have an Article 169 Approval for ATC Units which are subject to Certification and Designation processes via both EASA and SES related Regulations.

8 Part B Paragraph 3.1

The original text read

“UK Air Navigation Order Article 169 approvals are currently required to be held by Air Traffic Control service providers, but also act as the UK means for the Designation of UK ATC ANSPs.”

But the new text reads:

“Certificated ANSPs are required to be designated by the UK CAA in order to provide services in the UK.”

As above the new text either implies that the Oceanic Service is subject to EU rules or outside the scope of CAP 670, and we know from conversations that SRG believe neither of those statements to be correct.

Please see response to comment no. 7.


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9 Part C COM 01 paragraph 7.6.4

We are unclear as to the rationale for this requirement in COM 01 and it could potentially prevent the use of some of our current offline investigation tools and techniques. It also contradicts the requirements in 16.2 of SUR 10 (which has been rewritten and is open for consultation) which we would expect to be consistent with this requirement if valid.

The intent of the requirement is to ensure a verifiably correct original copy is made for SRG and AAIB use and also to ensure that the information remains secure if the media were to be lost in transit to those authorities. It is not the intent to prevent local investigations. The security aspects for surveillance recordings are considered less critical and the current recorders aren’t able to achieve the same level of encryption.

The text shall be amended as follows:

For security reasons data exported as an ‘original copy’ to removable media for AAIB or SRG use must be in a format that can only be replayed on a dedicated replay machine or original recorder. Secondary copies made for local use only may be in an open format.

10 SUR 01 paragraph 7.1.1

Appears to contradict the information in Tables 1 & 2. We disagree that paragraph 7.1.1 contradicts information in tables 1 and 2. We presume this comment is made, that since in Tables 1 and 2 there are environments where non-co-operative surveillance is optional but not mandated. We recognise that, and this is why in paragraph 7.1.1 the word “normally” is added to the existing CAP 670 SUR 01 section 8.2. Apart from presenting the information in tables for added clarity, no changes have been made to what is fundamentally mentioned in the existing CAP 670 SUR section.

11 SUR 01 paragraph 7.1.3

Whilst this seems reasonable, we don’t understand why this would apply to Non-Cooperative systems but not Cooperative systems. This seems to suggest that SRG view PSR as key, and you can continue to provide a service with PSR only. Whilst there may be a few regional airports that can continue with this assumption, we don’t believe it is valid anywhere else.

The CAA’s view that PSR (Non-cooperative techniques), as stated in paragraph 7.11 “is normally the minimum level of equipment necessary to provide Radar Control, Traffic Service or Deconfliction Service”, has not fundamentally changed. Note also that this is existing policy stated in the current CAP 670 SUR 01 section 9.2 and 9.3 and that no change has been made by this amendment.

Where PSR is provided, it is needed for a reason; primarily to detect the non-co-operative targets. Unless another non-co-operative surveillance source is available it is difficult to replace this function. If the CAA makes this equally applicable to co-operative systems, that means there is no minimum requirement for co-operative surveillance. Note that the “remaining surveillance systems” stated in paragraph 7.1.3 may not be necessarily non-co-operative. Hence they may not be capable of detecting non-co-operative targets. This is why paragraph 7.1.3 cannot be equally applicable to co-operative systems.


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12 SUR01 paragraph 7.1.4

We don’t believe this is a reasonable statement. This suggests other means of mitigation are not considered valid, such as planning such withdrawals outside busy hours, ATC restrictions, or even an alternative source of co-operative surveillance.

This statement is about permanent withdrawal of a non-co-operative surveillance source. The word ‘permanently’ will be added to read “7.1.4 The co-operative surveillance system where provided shall not be permanently withdrawn from service unless the demand and complexity of traffic can be safely handled using non-co-operative surveillance alone.”


The text is unclear, can you please clarify. The text will be amended as follows:

“7.2.2 Terminal and en-route airspace where non-co-operative surveillance is not mandatory according to Tables 1 and 2, non-co-operative surveillance is required in addition to those listed in the tables wherever an ATSU providing surveillance based air traffic services identifies that it is probable for non-transponder equipped aircraft, whether identified or not, to present a hazard to operations due to the uncertainty of their positions, which cannot be mitigated by other measures.”

This means that where non-co-operative surveillance is not mandated as per tables 1 and 2, i.e. where non-co-operative surveillance is optional, where there is a risk to flight safety due to the presence of possible non-co-operative targets, and if such a risk could not be addressed by other means, PSR is required.


Appears to concrete us into providing non-cooperative solutions forever. Is FIS considered a surveillance based air traffic service? Who’s going to pay for this given the current challenges with the unit charge?

There is no intention to mandate non-co-operative surveillance forever. However, it is the CAA’s view that PSR/non-co-operative surveillance is the normal minimum requirement (as stated in 7.1.1) and this has not changed for the short and medium term. The CAA has initiated work to review surveillance strategy for the UK, with the intention of providing maximum flexibility to the ANSP in terms of the systems they can implement, and the true requirements for having PSR is under debate.

As stated in CAP 493, “Air Traffic Service” is a generic term meaning variously, flight information service, alerting service, air traffic advisory service and/or air traffic control service (area control service, approach control service or aerodrome control service). This is an ICAO definition. Types of surveillance services in controlled and uncontrolled airspace are defined in CAP 493, Chapter 5, Section 1.2. These are existing terms; therefore the CAA does not understand why there is confusion about charges.


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“Airspace where types of surveillance techniques are not mandated or prescribed”. Where would this be exactly? Could you please give an example?

The term “terminal environment” could also include Control Zones (CTZ) for example which are not specifically included in the table. They normally extend from the surface level up to about 2,000 ft. (Ex Heathrow). We recognise that the policy will need to be reviewed and better defined, and work has already begun internally within the CAA to review the existing policy and wording under the Future Surveillance Strategy work, however for the purposes of this amendment, it was only intended to present the policy in a table format for clarity with no fundamental change to the existing policy.

A note has been added to improve clarity and wording changes as follows:

7.2.4 In airspace not identified in Tables 1 and 2, if providing services in an environment where there is a mixture of non-co-operative and co-operative targets, where surveillance services are provided exclusively using co-operative surveillance techniques, methods necessary for the safe separation of targets shall be defined and justified.

7.2.5 The choice of surveillance techniques for the intended application shall be justified based on a hazard identification, considering equipage levels in the operational environment.

NOTE: The proportion of co-operative and non-co-operative targets and the possibility of presence of co-operative targets with faulty equipment in the intended coverage area must be considered.

NOTE: The choice of co-operative surveillance techniques could be SSR Mode S, ADS-B or MLAT, where as the choice of non-cooperative techniques is limited to PSR although multistatic radar maybe a feasible option in future.


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16 SUR01 Table 1 We would like to see the justification and thought processes that resulted in the decision that PSR is not required above FL100. Why FL100? Why not FL50 or FL120? This suggests that SRG recognise that the principle role of PSR in such areas is as a Safety Net (i.e. An infringement detection tool) rather than a means of precisely controlling & separating aircraft, a role that co-operative surveillance is more suited too. It doesn’t seem to sit naturally with the statements made in 7.1. through 7.2.5. We believe this is important, as it suggests a change in SRGs previous stance and could significantly affect future XXXXX surveillance strategies.

It is not understood why XXXXX believe there is a change to SRG’s previous stance. The CAA would like to highlight the fact that this is not a new requirement that has been introduced in the 13th amendment to CAP 670. Since the text in SUR Ops (SUR 01) in the current CAP 670 is long and ambiguous, it is now represented in a table format for added clarity. Also the word “PSR” and “SSR” were replaced by “non-co-operative” and “co-operative” techniques, which gives more flexibility to the ANSP as regards the type of technique to be used. The fundamental position that PSR/non-co-operative surveillance is the minimum level of equipment necessary, has not changed. This is unlikely to be changed in the near to medium term since there still exists a need to detect non-co-operative targets. Unless all aircraft are known to be transponder equipped how can one provide a safe service only with SSR/MLAT or ADS-B like co-operative only technique? As stated in Annex E, the CAA has initiated work reflecting the Future Airspace Strategy (FAS) and other related Government imperatives to determine the best options for the surveillance infrastructure within the UK.

The rationale for not requiring PSR above FL 100, when this requirement was originated, is because according to UK AIP GEN 1-5, carriage or SSR transponder equipment with Mode S Elementary surveillance capability is mandated to all aircraft within the UK airspace at and above FL 100. Infringements are still possible above FL 100, but the reason for requiring PSR below FL 100 is to detect non-co-operative targets which are not necessarily infringers depending on the type of airspace they are in.


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17 SUR01 Table 2 We assume that Class G airspace falls outside of the formal En-Route environment. Confirmation would be appreciated.

The CAA is unsure as to what is meant by “Formal En-route environment”. No airspace is defined or formally designated as “Formal En-route environment”. En-route environment is a generic term used in Table 2 to refer to any airspace where flights are in en-route phase. This can consist of portions of controlled airspace and portions of uncontrolled airspace. The type of surveillance services provided depends on the type of airspace the flight is in. What is meant by “formal” is not clear since there is no such a thing as “formal en-route airspace”. We will however take these comments in to account and revise wording in the review of surveillance policy related to future surveillance strategy in the UK.

UK AIP ENR1.1-10 explains what Class G airspace means:

“The residual Airspace within the UK Flight Information Regions (FIRs) and Shanwick FIR which lies outside Controlled Airspace and Advisory Routes (Classes A to F) is designated Class G.”

18 SUR01 Table 2 Please clarify the definition of “High traffic Density” or “High Complexity”

There is no nationally or internationally defined definition for “High Traffic density” and “complexity”, although such definitions can be found in various Eurocontrol standards. These terms are not new to this amendment and are from the existing entries in CAP 670 SUR 01. We would however be willing to consider any suggestions or alternative wording to add more clarity to this section.


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19 SUR02 paragraph 2.1

The scope is clear that this applies to all surveillance systems. However some of this section appears to refer to surveillance of airborne aircraft (and not surface surveillance). For example, resolution requirements are made with reference to separation minima (not applicable on the surface). The document should be reviewed to confirm each requirement is appropriate for all surveillance types.

The word “separation distance” is used in paragraph 6.4.3 when stating resolution requirements, rather than the term “separation minima”, to make it generic to avoiding aircraft conflicting both on the ground and when airborne. However, if the use of the term separation implies airborne aircraft only, the CAA’s suggestion is to delete the text within brackets.

For paragraph 6.4.2.4, we will add the text “For separation applications” at the beginning of paragraph 6.4.2.

We have made it clear that these are generic surveillance systems and that it is up to the ANSP to justify that the required performance shall be specified and justified for the chosen application and the air traffic service provided in the airspace concerned. The attributes in paragraphs 5 and 6 are applicable to all types of systems that we are aware of. The other aspects are generic and may or may not apply to each system that exist or that may exist in future, but we have highlighted the generic aspects to consider for all types of existing and future systems.


This paragraph is unclear. Suggest that it does not add anything that isn’t already asked for in paragraph 6.4

The CAA agrees. Paragraph 6.2 shall be removed and the rest of the paragraphs will be renumbered.

21 SUR02 paragraph 6.4.2.4

Reference to separation minima not applicable to all surveillance systems.

The CAA agrees the term “separation minima” does not apply to surface surveillance applications.

The text shall be amended to add “For separation applications” at the beginning of paragraph 6.4.2.4 and “(i.e. half the separation distance)” in NOTE 1 under paragraph 6.4.3 shall be deleted.


Suggest replace “landlines” with a “datalinks” (more generic) Agreed.


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This paragraph is unclear. We don’t think Pd should be defined in terms of percentages of aircraft (implying perhaps that not detecting one aircraft for a lengthy period would be acceptable as long as other aircraft are detected).

It is not stated as an alternative way of defining Pd. Pd is a term that is well established and the CAA does not intend to redefine it. However, since Pd of 100% is not practically achieved, for example a 95% Pd would mean that it is acceptable to not to detect some targets at a given time. Loss of detection may occur due to faulty transponders as well as due to the radar’s limitations.

When providing an Air Traffic Service, it is important to understand how many such non-detected targets at any given update is acceptable for an ANSP to be able to continue providing the service in a safe manner; hence we have retained the requirement but have modified the text as follows:

6.4.10.2 For the intended application, the acceptable number of aircraft of the total number of aircraft in the coverage volume required to be detected…”


Linking amount of clutter to number of targets does not seem sensible. It implies you could tolerate less clutter in the middle of the night than at peak hours.

The CAA agrees that clutter should not be included here. The NOTE shall be modified as follows:

“NOTE: The criteria shall include the false targets including reflections, detection via side lobes of a radar, targets erroneously declared as aircraft targets by plot extractor systems and erroneous targets exceeding maximum allowable positional error affected on all co-operative and non-co-operative techniques being used.”


This requirement is similar, but not identical, to 6.4.2.4. The requirement in paragraph 6.4.2.4 was intended to be generic for all applications. However as XXXXX have pointed out, the word “separation minima” only applies to Separation application. Paragraph 6.4.2.4 will be deleted since this is covered by paragraphs 6.4.2.2 and 6.4.2.3 generically for all systems, and paragraph 7.1.3 will be retained as it is, since this is specific for separation application.


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Is this true for En-Route too? In which case do we report to ATSSD? Historically we have reported radar/radar interference to DFT/Ofcom for PSR interference, and DAP for SSR related issues. It contradicts the instructions for co-operative systems detailed in CAP 761 “Operation of IFF/SSR Interrogators in the UK”.

It was not intended to be for en-route since it states such occurrences should be reported to the Regional Inspectorate. Whilst the NISC process addresses interference to and from co-operative systems, requirement paragraph 8.1.3 is aimed at both co-operative and non-co-operative systems. Whilst the NISC interference investigation process is important and has implications to Ofcom licences, NISC approvals issued to an interrogator, when it comes to airfield surveillance systems, it is also important to SRG to be aware that surveillance systems are suffering from interference effects since this is a safety concern. This is why the SRG Regional Inspector needs to be aware of the situation. We appreciate XXXXX raising this point and we will add a note under paragraph 8.1.3 to say:

“NOTE: In addition, any interference effects affecting co-operative systems must also be reported to NISC for investigation as required by section 3 of CAP 761”.


A clarification of the word ‘compromise’ is required. I’m not aware of a single wind farm solution so far that doesn’t compromise the radar service in one way or another. The compromise is either manageable, addressed through change in procedure, or mitigated through another means. But in every case the original surveillance performance has been compromised. The statement fails to address who is responsible for ensuring this. Given that the turbine development could be constructed without NATS consent. Does that therefore mean HMG become responsible? In short this is an unsupportable statement.

The “required performance of surveillance systems” is explained in SUR 02 paragraph 4. We are aware that most wind turbine solutions degrade or compromise the performance of surveillance systems in one way or the other. The CAA is not referring to the original performance here. It clearly states the “surveillance performance required for the intended application”. As long as the surveillance system is used to provide the same service, it has got to meet the required performance to be able to provide the service. This statement is not about who takes the responsibility, it is rather a statement that is true for any application. For example if the system met the performance criteria required to perform a 5 NM separation, and if the ANSP still intends to provide 5 NM separation with the surveillance system, it has to meet that performance criteria to be able to continue to use the system for that purpose.


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28 SUR03 paragraph 2 Data links and plot combination are two unrelated concepts. It is not at all clear that it is beneficial to combine them into one section.

The CAA agrees that surveillance data combination can be considered as a topic on its own. It was felt that the content of paragraph 3 was not enough to permit a SUR section just for that topic. Also please note text in introduction and scope. The data transmission links are a key element of any single sensor system or any multiple sensor systems whether remote or local such as a Local Area MLAT system or an ORRD, hence we felt it was appropriate to include these two topics under a single SUR section.


Many radio links are provided by third parties e.g. BT. It is not always possible to provide evidence that they carry out safeguarding. There may not be the regulatory framework to allow such safeguarding in all cases. Perhaps it would be advisable to include a clause that where evidence for such safeguarding cannot be provided, the ANSP can show that there are other mitigations such as redundancy available.

The CAA agrees with this comment. A note will be added:

NOTE: Where the radio link is provided by a third party and evidence of safeguarding cannot be provided, then appropriate mitigation for interruption of the link shall be provided.


Change “received by a remote supplier” to “received from a remote supplier”.

Agreed.


We are not aware that this is ever done (e.g. on XXXXX ORRD). Suggest this recommendation is removed.

Agreed since this is covered by the APIIR Annex IV. Section deleted.


Combining of co-mounted PSR/SSR is almost always carried out as a function of the radar. Suggest this is moved to SUR04 or 05.

The CAA agrees that combining is almost always carried out as a function of the radar. The reason this could not be moved to SUR 04 or SUR 05 is that they are applicable individually to PSR systems and SSR systems. Hence this section seemed to be the appropriate place for combined PSR/SSR systems.


This is a basic radar requirement not a combining requirement. Agreed. The recommendation will be moved under PSR Geographic alignment of PSR in SUR 04.


If they are co-mounted they have to be geographically aligned. Azimuth alignment is already described in 5.1.1

Agreed. Paragraph 5.1.4 will be removed.


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There is not always an OR to use a PSR/SSR in PSR only. The requirement should be qualified with “if it is intended to provide an operational service in this state”

The text will be amended as follows:

5.1.4 Where the PSR active reflectors, PSR PEs or SSR Remote Field Monitors are used as an on-going performance verification technique in a combined PSR/SSR system, appropriate monitoring mechanisms shall still be in place during PSR or SSR unavailability for alignment checking purposes where PSR only or SSR only service will be provided.


Multi-sensor tracker would be a more generic term than MRT. Agreed. The text will be revised to read:

The following requirements shall be met as a minimum by systems such as Plot Assigner Combiners and Multi Sensor Tracking Systems that use multiple feeds for the integration of surveillance data.


This does not appear to be a sensible note. Who would co-mount two 2D radars!? With the exception of some obscure military applications, they’re never going to be co-mounted! Equally the slant range error can be corrected. Otherwise we would not be able to utilise PSR only in MRT systems…..which we do.

This comment is not understood. Both PSRs and SSRs only measure range and azimuth and do not measure height information. It is true that SSR can transmit pressure altitude information, but the SSR is not capable of making a 3D measurement. Hence we consider that normal PSR and SSRs to be 2D whether they are co-mounted or not. The CAA is aware that there are various methods to correct a slant range error, but in each method some elevation information is necessary. 3D radars give height information which can be used for slant range correction. If there is an SSR, the Mode C information is used in the absence of height data. Other methods assume a default altitude depending on the context the aircraft is at a given time. To add clarity, the note will be reworded as follows; We believe the revised wording addresses potential confusion:

NOTE: If the radars are not co-mounted, there will be a difference in their slant range measurement of the same target by each radar. Altitude or height information of the target is necessary for the slant range error correction process.


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This paragraph is unclear, please clarify Most combined systems display the position information as range and azimuth information where a radar sensor is involved, although the position is not originally measured in terms of range and bearing. For example, where PSR and MLAT systems are used, MLAT position information is also displayed as range and azimuth data and the location of the PSR radar is used as the reference point. This may however not always be the case. This requirement was included to understand the format by which position information is displayed to the controller and to understand the reference point used for measurement.

A note will be added for clarity:

NOTE: For example, position information can be displayed as range and bearing with respect to the position of a radar head used as the reference point.


The meanings of these terms should be defined. Also it is not clear what testing them means with regard to the multi radar tracker.

The multi sensor tracker may use various tracking algorithms when fusing surveillance data from multiple different surveillance sensors. These may introduce delays, position errors, track discontinuities across the boundaries between sensor sources, track jumps if not known as track jitter when the position jumps between the sensors (e.g. where a target may have no line of sight to one sensor, hence no data from one sensor for that target for a short period of time), dual tracks for the same target specially across the boundaries between two sensors or false tracks when the tracker may be confused by excessive false plots coming from a wind farm etc. The requirement will be modified as follows: The methods used to integrate positional information from multiple surveillance sources may introduce features that may impact on the accuracy and the ability to apply a certain separation standard. The impact of these features on the ability to support the defined operation shall be assessed. Such features may include: Lag in turns Track discontinuities e.g. across the boundaries between sensor sources Track jumps Track deviations


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Split Tracks False Tracks


Presumably this section is addressing the effect of loss of a surveillance feed (perhaps “sensor” would be a better term) on the performance of the MRT. If so it should state this.

The CAA understands XXXXX comment. Whilst the word “sensor” also seems like a better term, the word “feed” is used with the intention to make a distinction between a single surveillance system formed of multiple sensors such as MLAT and one that uses data from different individual standalone systems. Hence the title of section 5 is stated as “Combined Surveillance Data from Multiple Surveillance Systems” rather than from “sensors”. For example if a PSR and MLAT is fused, one can wonder if we mean the individual data feeds within the MLAT system or whether the whole output of the MLAT system should be considered as a feed. But when we say a “sensor” each MLAT sensor is a “sensor” but this is not what we mean for the data fusion process.

On reflection, the text in paragraphs 5.2 and 5.3 will be amended as below for added clarity:

5.2 Requirements for Systems used for Combining Surveillance Data from Multiple Systems

5.2.1 The following requirements shall be met as a minimum by systems such as Plot Assigner Combiners and Multi Sensor Tracking Systems that use feeds from multiple systems for the integration of surveillance data.

5.2.2 The data feeds from the individual surveillance systems used for the combination process shall be defined including the following elements:

5.3 Loss of Data Feeds from Individual Surveillance Systems

5.3.1 The impact of the loss of data from individual surveillance systems on the accuracy and the ability to provide surveillance data to meet the operational requirement shall be assessed.


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The use of IP data, and in particular UDP links means this is not feasible. However, it depends on the definition of ‘system’, if system includes the appropriate design assurances, people, process, and other monitoring techniques the risk of such an overload can be controlled and managed.

This is an existing requirement. However the comment is noted. This requirement will be reviewed in due course. In the mean time paragraph 5.4.1 will be deleted and the text in paragraph 5.4.2 amended as follows:

5.4.2 The system shall provide automatically through the display system or procedurally to advise the controller of an overload situation on the links.

To help us review this requirement to suit the current environment, we would like to understand how XXXXX, when providing radar data to third parties, know that there is an overload on the link and whether some of the data were shed by the system as a result.

42 SUR03 paragraph 6

We believe this section is unnecessary. CAP 670 applies to all operational systems, so it is unnecessary to reiterate that it applies to redundant systems.

The CAA understands XXXXX comment. However, certain ANSPs do not appear to realise the difference between a truly redundant system and a system of which its contribution is necessary for what is considered as the “normal operation”. For example, where PSR and SSR data is necessary to provide a service, the data supplied by the SSR is required for the operation, hence the loss of SSR means there is an impact on the service being provided. However there may be a second SSR that is a redundant SSR, of which the loss is not altering or impacting the service being provided. We feel it is necessary to make this difference clear to ANSPs, meaning that it will be retained for the time being.


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We question the regulatory need for this section. Frequency assignment, stability, bandwidth is covered outside CAP 670. We believe there is at least one surveillance system in the UK that does not use these frequency bands.

The CAA agrees with this comment. These provisions are more related to the DAP Spectrum management functions, however such requirements are not published in any DAP document or other CAA document. However, having a separate document would mean that users would have to look at a number of documents to find the regulations applicable to the equipment. We have the long term objective to review the requirements and regulations with regards to spectrum characteristics of PSR systems and other surveillance systems, and the means by which compliance with the regulations can be demonstrated. In the interim we believe it is useful to retain the requirements on spectrum related aspects in CAP 670 than having them mentioned nowhere, and therefore we have retained and updated the text in this section in accordance with that mentioned in ITU regulations. In the longer term we intend to gather all spectrum related requirements related to SUR systems into one document, potentially to be included as an Appendix to CAP 670 for easy reference.


It would be useful to include “terrain” as well as local obstructions. The need to ensure that the system has line of site with targets is not limited to PSR, therefore this could be in SUR02.

Agreed. This has been moved to SUR 02 under Section 9 ‘Siting requirements’ and the words have been amended to be more generic rather than specific to PSR as follows:

9.4 Siting Requirements for Sensors

9.4.1 Local site obstructions and terrain effects shall be shown to be acceptable for the required coverage (337).

9.4.2 Recommendation: This should be provided by a 360 degree representation giving the elevation (in degrees) of any obstruction versus bearing and a ‘line of sight’ coverage chart for several target heights based on these obstructions and using the Radar earth curvature (338).


This requirement is addressed by SUR02 section 6. The CAA agrees that the required performance of surveillance systems is addressed generically by SUR 02. However, it was felt that the inclusion of the NOTE in this section is helpful when expressing performance specifically with respect to a PSR.


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Should consider whether this section applies to SMR as it is currently written.

We have considered this but do not believe any change is necessary to the existing text. Since SUR 09 clearly addresses “Surveillance Systems for Airport Surface Surveillance including SMR specific section” we assume the context in SUR 04 where the word “PSR” is used is understood by the readers.


What is the regulatory basis for including SRAs only in the PSR section? SRAs could be provided using, say, SSR subject to a safety case being provided by the ANSP.

This has been a topic that has been debated with XXXXX many times. Traditionally, requirements for SRAs were included under PSR since SRAs with SSR only was not encouraged by the CAA; although we accept that it is possible to provide SRAs wither other surveillance technologies. The key concern was the transponder failures and malfunctioning transponders reporting wrong ranges. In addition to the impact of track smoothing effects, processing delays were also amongst the concerns raised. We understand that XXXXX have greater confidence in SSR technology as XXXXX consider SSR position to be the principle position when combining PSR/SSR data. Provided that a robust safety argument could be provided by the ANSP we have agreed to consider allowing SRAs based on technologies other than PSR. This is however not a view that the CAA want to encourage due to concerns with transponders, which are outside of an ANSPs control. We suggest retaining this under PSR but to add a note under section 4 title stating:

NOTE: SRAs may be provided using surveillance technologies other than PSR provided that a robust safety argument is presented by the ANSP addressing all risks and the CAA is satisfied.


The accuracy requirements would be better expressed in absolute values. As the old requirement for the radar to be within 37 km has been removed it is conceivable that a 1°/5% accuracy could lead to some very large errors.

The CAA agrees with this comment. The text will be revised as follows:

4.3.1 When used for surveillance radar approach (SRA) purpose, the accuracy of the position information shall be justified as suitable for SRA within the range where SRAs are performed.


“The Mode A code for the RFM shall be 7777”. This effectively contradicts the recommendations of 7.3.3 (Page 35) as to check that the Mode A code change is correctly processed by the sensor requires the RFM to use a Mode A code other than 7777 to detect a change.

The CAA agrees with this comment. The text will be revised as follows to make it consistent with the text in UK AIP ENR 1.6 section 2.2.4:

7.4.7 The Mode A code for the SSR RFM shall be 7777 and/or 7776 unless stated otherwise in the SSR approval certificate.


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Suggest change “configurable depending on the OR” to “configured to meet the OR”.

Agreed.


Bullet b) appears to be contradicting the directive in 5.3 above. There is an error with the original text. It will be corrected as follows:

5.3 Interrogations from multilateration systems shall not set “lockout” on any targets.

The text in paragraph 6.3 is that mentioned in the Mode S IR that is applicable to all Mode S interrogators. As such the conditions therein are applicable to Active MLAT systems that are capable of Mode S.


This paragraph is not needed. 9.1 already addresses what is required.

Agreed. Paragraph 9.3 will be removed.


A-SMGCS MLAT typically use a test transmitter (not transponder). The regulator should consider rewording this unless it feels this is inadequate.

The words ‘Remote Field Monitor’ will be used. MLAT systems use SSR site monitors as a means of measuring on-going system performance. For example, NATS North sea system contains five SSR site monitors manufactured by Beel Technologies Limited for system monitoring. Since ‘RFM’ is used elsewhere in CAP 670, the same words will be used here for consistency.


Use of test transponders can be problematic for wide area MLAT. The spread of receivers makes it difficult to maintain line of site with test transponders. It may be impossible to comply with a reasonable system design.

The CAA wishes to clarify that this statement does not require the RFMs to be the only monitoring mechanism that monitors the MLAT system. We agree that in Wide Area MLAT systems, it is difficult to achieve Line Of Sight with all of the Remote Units with one site monitor. Most MLAT systems have in-built system testing and monitoring capability and, in most cases RFMs provide additional means of monitoring, so they re-inforce or add confidence regarding the system status. Every WAM system that has been deployed in the UK contains RFMs as a means of system status monitoring.

Paragraph 12.2 is included to recognise that RFM may not be the only method of system performance monitoring.

Paragraph 12.1 will be modified:

“The MLAT system shall use at least one Remote Field Monitor (SSR site monitor) for on-going system integrity and end-to-end performance monitoring.”


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A requirement to use the “best data output mechanism” seems open ended.

Agreed. The text will amended to read:

15.1 The data output rate shall be identified and the MLAT system shall use the data output method that gives the highest quality and positional accuracy of data.


There is nothing particularly different about MLAT’s ability to meet low level coverage compared with SSR. Both can be affected by terrain (MLAT has perhaps more flexibility to deal with it). This paragraph is not necessary.

The CAA agrees that both SSR and MLAT coverage can be affected by terrain and MLAT has more flexibility to deal with it. However it must be recognised that SSR is a single sensor system with a more consistent shape or area of coverage at a given altitude (subject to retain effects) whereas an MLAT system contains multiple sensors where each sensor may be situated at different heights from the ground, and at various distances all of which contribute to the overall surveillance coverage achieved collectively by the system. In all MLAT systems SRG have come across and approved to date, the low level coverage has been more difficult to achieve than at higher levels, and the area of coverage varies on the sensor distribution which has to be demonstrated through suitable performance assessment method.

The note will be amended as follows so no comparison is made with the radar:

NOTE: MLAT system coverage and probability of detection can significantly vary across vertical levels. The probability of detection may be lower than the required criteria at lower altitudes.


Covered in SUR02 section 6. Whilst SUR 02 addresses key performance parameters relevant to any ground based surveillance system in generic terms, it does not give any technology-specific requirements or recommendations specific to multilateration technique. This section addresses the performance that should be expected by an MLAT system. For example, with MLAT technology it is expected that a false target count would be much less than a radar, and same applies to ADS-B. The CAA therefore feels this section is relevant and will be retained.


The only number of targets lower than 1 is none. The CAA agrees with this comment. This was intended to be a %. The text will be corrected as follows:

18.2.1 Recommendation: The number of false targets during any update should be less than 1%.


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We don’t understand the need or benefit of recognising UAT or VHF DL Mode 4. This just introduces ambiguity as to whether it is considered useable in the UK or not and confuses the aircraft equipage needs within UK airspace. Suggest removing all references to either technology (other than to say perhaps it is not viable in the UK).

It is true that Mode S ES is an accepted ADS-B data link medium worldwide and that Europe has also chosen 1090ES as the primary physical layer for ADS-B. This is because the SPI IR mandated Mode S ES squitter ADS-B equipment on aircraft meeting certain criteria. A secondary data link medium has not yet been selected between UAT and VDL Mode 4 for Europe. Furthermore, the SPI IR does not mandate ADS-B ES capability on all European aircraft and it does not prevent a secondary medium being applied as suitable to national and European environments.

Also, various data link mediums have different benefits. For example, VDL Mode 4 is known to be best used for short message transmissions from a large number of users. VDL Mode 4 systems are capable of increased range in comparison to 1090ES or UAT systems. The SPI IR requires that ANSPs implement the most efficient deployment solutions taking into account local operating environment etc. Provided that the ANSP provides a robust safety argument for using a medium which is best for their needs, the CAA has no reason to object. Furthermore it is known that some European states are trialling VDL Mode 4-like technologies as a secondary ADS-B medium and airborne equipment capable of supporting more than 1 medium are also being explored. The CAA believes it is necessary to identify the alternative techniques and we do not believe this causes ambiguity.


Note 1 & 2. As per the above comment, these notes are unhelpful as they simply introduce ambiguity. Who is ‘The implementer’ in this scenario? Why would we expect to provide services to suitably equipped aircraft when we’ve mandated 1090 ES?

See response to comment no. 59.


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It’s not clear who is accountable for the airborne elements. It’s certainly not the ANSP (we would have thought this was a government obligation to the ANSP). We cannot recall airborne aspects being mentioned elsewhere in CAP670. Should this not be covered in some other form of documentation? i.e. Aircraft related regulation, type approval.

Carriage of transponder equipment is published in UK AIP GEN 1-5 Section 5.3. Currently published carriage requirements are limited to SSR only. Transponder Mandatory Zone airspace is also published in the same section in the AIP. The transponder carriage requirements and the standards that must be met are usually published in ICAO SARPS, SES Implementing Rules, EUROCAE and RTCA Standards, EASA certification specs etc. For ADS-B ES, carriage requirements are published in SPI IR, however additional carriage requirements should be developed nationally to suit the UK airspace requirements. By imposing National carriage requirements and defining airspaces where carriage of particular type of transponders is mandatory, the CAA is able to help ANSPs as the national regulator. However, more discussions need to take place involving ANSPs before imposing such requirements, since such policy decisions need to take ANSP’s future surveillance strategies into account. We have initiated work to review the transponder carriage requirements, airspace policy decisions related to ADS-B internally, but until such decisions are finalised, the intention was to refer to the existing ADS-B requirements in CAP 670. By stating all these requirements in one place, we do not intend to make the ANSP responsible for airborne equipage or the standards such equipment must meet. However, unlike for radar, the ANSP solely rely on an airborne system to give the position information, therefore to provide a surveillance based ATS. The ANSP must therefore be able to argue that the performance of such data are adequate to provide an Air Traffic Service. This can be done by referring to the performance data defined in applicable standards and regulations and through monitoring data (e.g. The CAA monitors GPS signals for its performance). This text intends to ensure is that an ANSP using data from airborne sources to be confident that the data they are using is suitable to provide an air traffic service.


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Who is this directed too, the ANSP? How will the ANSP know in real time whether an ADS-B installation has been certified or which meets the performance criteria. Who is going to be responsible for ensuring this is in place, it seems inappropriate to place the emphasis on the ANSP.

The CAA is not saying here that the ANSP is responsible for making sure the airborne equipment are certified and meet the appropriate standards. It is European regulation as well as national transponder/airborne equipage carriage requirements that must impose requirements for the airborne equipage as well the standards to me met by those systems. No such meaning is implied here by the text.

It is however known that there are many variations of ADS-B airborne standards and equipment types. Since ADS-B is not operationally implemented in the UK, we believe there should be a pre-operational trial period which has to monitor the various equipage levels and the standards they are capable of meeting. For example Eurocontrol conducted ADS-B airborne monitoring project and revealed statistics about the various levels of ADS-B equipage in Europe and the standards met by them. If ADS-B based air traffic services are to be provided, the ANSP must be able to justify the appropriate environment exist for the safe service provision. Apart from SPI IR, no national requirements are imposed on ADS-B airborne domain at present by the CAA. Of course, more discussions are necessary between the regulator and the ANSP, should an ANSP expect to introduce ADS-B based air traffic services in the UK.


The same comment as for 5.5 & 6.1 above but in addition there appears to be no recognition that ADS-B is a dependant form of cooperative surveillance and the expectation this places on the regulator.

The CAA agrees with the first comment. This was not intended to place any emphasis on the ANSP regarding airborne equipment. The revised text is given below:

The vertical position information shall be processed by the ground based surveillance system equivalent to processing Mode C information from SSR.

NOTE: This is to ensure same level of data integrity is maintained by the ground system when processing altitude information received from ADS-B equipment.

Regarding the second point: We do not understand the rationale for making such a comment here. It is needless to say to ANSPs that techniques such as SSR, ADS-B and MLAT are co-operative surveillance techniques. A co-operative surveillance technique is a co-operative technique and the intention here is to identify the requirements that are relevant to this particular technique. Whether it


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suits the type of service and the environment that it will be used for is to be argued by ANSPs who implement such techniques. There is no reason for a regulator to prevent anyone from implementing techniques that are argued as suitable and appropriate to meet the safety levels. Is XXXXX suggesting that the CAA should prescribe what techniques to be used by an ANSP? We believe this comment relates to the UK Surveillance Strategy topic which we have commented on in response to previous questions.


A more positive statement needs to be made suggesting which of the two should be made. To mix the two together is a recipe for disaster. To that end I would suggest only barometric is used for the purpose of separating aircraft.

The CAA agrees with this comment. This was written not to suggest that an altitude other than barometric can be used for the purpose of separating aircraft. The note clearly states “only the barometric altitude is allowed to be used for ATS applications”.

However, the CAA agrees that paragraph 9.7.3 has the potential to cause some misunderstanding. The text will be revised as:

9.7.3 Only barometric altitude shall be displayed to the ATCO for separation purposes.

NOTE: Some avionics may allow aircraft to transmit geometric height in the ADS-B message although only the barometric altitude is allowed to be used for separation applications.


Why is this mentioned for ADS-B but not SSR? This is a valid comment. Considering this is standard practice when using altitude for separating aircraft this requirement will be deleted.


What is the proposal for the provision of service in the event the quality criteria from the aircraft are not acceptable? You can’t simply ignore it!

We don’t believe it is for the CAA to decide what to do in the case of aircraft not qualifying the required quality indicator criteria. It is to be argued by the ANSP who is wishing to provide an ADS-B based air traffic service. The entire purpose of having the quality indicator messages in the ADS-B reports is so that they are monitored by the ground, and those qualifying are known as meeting the operational standards. Some ANSPs in Europe appear to either discard the messages not meeting this criteria, or display the position but flag it on the HMI so the controller is aware and the appropriate procedure can be applied or precautions can be taken. It is for the ANSP to complete the risk assessment and come up with a proposal.


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Is this not more a display requirement? Partially agree. One could argue either way, but it can only be displayed if a data item (emergency indicator in this case) coming from the airborne system is available and correctly processed by the ground system. So it is also RDP and a display requirement for systems using such airborne data.


The use of ATM to provide an approach service (for example at night) is being investigated. The NOTE in this paragraph should be qualified. Perhaps add “without a full safety assessment being carried out.”

Noted. CAP 493, MATS Part 1, Section 2, Chapter 1 Page 14 states:

“Operation of an ATM is not associated with a particular rating and must not be used as an ATS surveillance system to provide Approach Radar Services.”

If we add XXXXX suggestion into the note, it will mean, with a full safety assessment carried out, the ATM can be allowed for Approach Control services. The CAA has not made such a policy decision to date although we are aware that XXXXX is looking at this possibility. Until such a policy decision is made we suggest that CAP 670 is kept consistent with the current policy in CAP 493.

69 SUR09 paragraph 1 It might be worth mentioning vehicle tracking systems. Text will be added as follows:

1.1 Surveillance sensors play a crucial role in systems used for airport surface surveillance such as SMGCS and A-SMGCS. The surveillance sensors providing data for these systems may comprise of a single non-co-operative sensor such as a Surface Movement Radar (SMR) or a combination of a non-co-operative and multiple co-operative sensors. While ADS-B can be used as a form of surveillance technique for detecting co-operative targets including vehicles, local area multilateration is a popular form of surveillance in surface movement surveillance systems for detecting co-operative targets in the airport environment.


We don’t think this definition works. The minimum legitimate distance between objects can be zero e.g. aircraft and tug. Suggest you might just use the form of words in 5.7.1

Agreed. The text will be revised as below:

5.6.1 The horizontal resolution of the sensor equipment shall be determined by a safety assessment for the specific aerodrome.


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71 SUR09 paragraph 9 As stated in 2.1, SMGCS is not just surveillance, and need not even include SMR. This requirement therefore seems beyond the scope of SUR.

The CAA agrees with this comment. Although a surveillance system does not essentially need to be part of an SMGCS, this section was included to recognise the possibility that a surveillance sensor could be an element of an SMGCS, hence the need to give due consideration to the surveillance element of it. It was also used to emphasise the difference between A-SMGCS and SMGCS (if and where a surveillance sensor is involved). The text will be revised as:

9.1 Where surveillance sensor/s form part of an SMGCS, a local safety assessment shall determine the safety impact in the event of failure of any element of the surveillance system.

9.2 A local safety assessment shall also justify the suitability of the functional and performance requirements of the surveillance system used as part of SMGCS.


The movement area includes aprons and gates. Labelling in these areas is undesirable. Suggest movement area is changed to manoeuvring area.

The text will be revised as follows:

12.1 The A-SMGCS shall provide identification and labelling to all authorised aircraft and vehicles on the manoeuvring area, and on other movement areas as required.


A 10s restart time is unachievable. We have revised this and researched into what current systems achieve and the start time stated, in material such as EUROCAE ED-117. The revised time is changed to less than 3 minutes.

12.4 Upon re-starting, the system recovery time shall be less than 3 minutes. Upon re-starting, the system shall restore the information on current traffic and system performance.


The meaning of this is unclear, please clarify. The A-SMGCS systems perform planning functions to accommodate requested movements for a future time, e.g. up to an hour. To do this it has to detect likely conflicts and take into account many other factors. On reflection, it is realised this is relevant to the overall processing system of the A-SMGCS system and not specific to the surveillance data processing system, although surveillance data may be used in this activity. We have therefore deleted this recommendation.


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The requirement for faithful recording of clarity, brightness, etc, goes too far. Many of these relate to particular conditions of the display itself and will not be recorded from the video input.

The CAA agrees and the text shall be amended as follows:

10.3 The recording system shall have the capability to record ATG data at a suitable refresh rate and display resolution and shall faithfully record all the features displayed to the controller at the time of screen capture.


We are not sure why this is necessary? Note that this requirement has been in place in CAP 670 for some time and is not a new requirement introduced at this time. In the case of an accident, when data is required by the AAIB for accident investigations, the staff at the ANSP must be able to provide visual replay and these procedures are normally recorded in the ANSP’s MATS Part 2 for them to follow.


It is unlikely to be possible to be able to replay TTW recordings made offsite (as allowed in para 6.2) simultaneously. The use of the phrase time-synchronised is preferable.

The text will be changed as follows:

16.1.3 It shall be possible to replay audio and TTW or ATG recordings simultaneously in a time-synchronised manner at the ANSP replay station for any controller position of interest.


CCDS is the name of a system. A more generic term would be preferable.


4.5 The presence of co-operative and non-co-operative surveillance input signals and CCDS code call sign conversation data signals shall be continuously monitored by the system.

79 SUR11 paragraph 7d

75Hz refresh rate is unnecessary with modern displays. Suggest this recommendation is deleted

Agreed. The recommendation will be deleted.


Surveillance coverage is 3D. Displaying this would be complex. This requirement is hard to achieve. The benefit to ATC needs to be established.

Understand XXXXX comment. We agree that this requirement as it is written is not feasible. The intention was not to represent a 3D diagram of coverage (although the wording suggests so), but where the actual surveillance coverage detected by a system is not a simple area that can be represented by a range value (e.g. MLAT 2D coverage area can be complicated, such as the North Sea system), the need to accurately represent the achieved coverage to the controller on a 2D display. Having further investigated into the issue we have decided to delete this requirement.


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A reference is needed. A Reference will be added as follows:

11.3 The system shall comply with the European Union Low-Voltage Directive (Directive 2006/95/EC http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2006:374:0010:0019:EN:PDF).


This should be qualified, as it may only be necessary to differentiate if ATC will make different decisions depending on the sensor source.

It is well established practice that PSR, SSR or other co-operative only target reports, combined target reports and coasted reports are displayed in different symbology in the ATC environment. Of course this must be known by the ATC personnel, since reports from various sensors and actual/predicted target reports have a safety significance and the data items received from each source differ in many ways (i.e. number of data items, accuracy and integrity levels etc). The CAA does not believe any change is necessary to this text.


XXXXX has concerns about this recommendation, as it allows a target to be completely hidden based on a single data field, which can become corrupted.

If the CAA understands this comment correctly, XXXXX is concerned about is the fact that once ATC applies the filtering function based on a particular parameter, if that parameter had been corrupted in some way, this may allow the wrong targets to disappear from the screen. It is a possibility as long as non-perfect systems exist which are not completely free of corruption and of course such an occurrence depends on the rate of corruption caused by the system.

The CAA does not understand what XXXXX expect by raising this comment. Filtering is a useful function to ATC which the ATC use currently and has been using for a long time and different systems have different filtering capability and criteria that can be applied. The idea of filtering is either to completely remove targets that are not of interest to the controller at a given point in time, or to remove some data elements that are not required to be displayed in some circumstances. This depends on the controller’s needs at a particular unit.

The recommendation here is to say that if filtering is applied, targets which match that filtering criteria must be completely taken off the display and it should not display the position of those targets which are meant to be filtered out.


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XXXXX concern is about the consequences of applying the filtering function based on a parameter that can be corrupted; however, the CAA recommendation is about completely removing the targets which the controller wants to be filtered out. Is XXXXX suggesting that even if the controller wants to filter out targets (for example the filter criteria being all targets above FL 150), these targets must not be completely removed from the screen, but at least the position symbol must be remained since there is room for corruption of data?

The CAA does not see a requirement to change the existing text.


If symbols representing the dimensions of the target (e.g. on A-SMGCS), then the symbol size should vary.

This comment is true to non-processed (non plot-extracted) primary radar sources showing a blip representing target size as seen by the radar (hence to the SMR element of the A-SMGCS).


12.5.1 Recommendation: The symbol size from plot-extracted systems should not vary with displayed range (572).

85 SUR11 paragraph 15.1/15.4

Modern displays do not suffer from colour drift like CRTs did. Calibration is no longer needed.

We agree with XXXXX in the sense that the common wisdom is that the LCD/TFT monitors drift at a much slower rate than CRT monitors do or do not colour drift at all. The problem with CRT monitors is that the phospors age with use, although not as rapidly as CRT displays. Evidence available from users of modern display systems suggest that the colour in Modern displays also drift over time. Some links below show discussions on the colour drift effect on LCD displays.

http://photomusings.wordpress.com/2008/06/20/persistence-of-vision-part-ii/

http://photomusings.wordpress.com/2008/05/24/persistence-of-vision/

http://toastycode.com/blog/2008/02/05/lcd-scrub/

http://ddisoftware.com/tech/computer-hardware/monitor-calibration-drift/?wap2

Although the chances of it happening in an ATC environment is not exactly known, evidence suggest that LCD monitors can also suffer from Image Persistence. There are both software and hardware tools

http://photomusings.wordpress.com/2008/06/20/persistence-of-vision-part-ii/�

http://photomusings.wordpress.com/2008/06/20/persistence-of-vision-part-ii/�

http://photomusings.wordpress.com/2008/05/24/persistence-of-vision/�

http://toastycode.com/blog/2008/02/05/lcd-scrub/�

http://ddisoftware.com/tech/computer-hardware/monitor-calibration-drift/?wap2�

http://ddisoftware.com/tech/computer-hardware/monitor-calibration-drift/?wap2�


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that allow calibration of colour in modern displays. However, the need to have the colour set calibrated at regular intervals depends on how critical the use of colour is to the tasks that the controller is performing. The colour perceived by the user can also depend on the viewing angle and how well engineered the system is for maintaining colour accuracy. Since we cannot rule out the possibility that colour drift can happen in modern displays, and since colour calibration can be carried out with simple software tools without necessarily buying specialised tools, these requirements will be retained in this amendment. The use of colour in an ATC environment and the associated human factors need to be looked at in more detail and more research will be necessary in some areas to understand the requirements for ATC display systems.


It is hard to imagine anyone wanting to use viewing hoods. Suggest this recommendation can be retired?

Agreed. Paragraph 16.3 and the associative note will be removed.


Given the stability of modern displays, this requirement is no longer needed. It is doubtful that it is truly being complied with now, anyway.

This is a human factors related issue rather than to do with the surveillance display stability. The text in this section will be revised as follows:

17.1 Colour alone shall not be the single factor used for distinguishing information between multiple sets of data that are presented in a similar manner on the display. (628).

17.2 The use of colour shall not conflict with the reserved meanings of colour use conventions in ATC displays.

17.3 Recommendation: Displays should not use colour for decluttering, however if used, it should be ensured that the contrast control is not available in normal use (629).


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XXXXX has been told verbally that mosaics used for small wind-farm areas do not need to be marked. Can this be included here?

We understand XXXXX suggestion to include such a statement. This requirement is written more generically to any situation where a surveillance picture comprises of multiple areas combined together.

With regards to specific guidance regarding wind farm mitigation solutions, The CAA is in the process of preparing guidance for industry to be published soon where display issues such as this have been captured. The guidance is that ANSPs should assess whether it is necessary to mark the boundary of such areas to be displayed to ATCOs based on a number of factors listed therein. Further information can be provided if necessary.


What is the regulatory/safety need for this requirement? There are situations where controllers would want to enter some free text, e.g. SSR codes/comments which might be safety related. Most display systems have some capability to allow the controller to do this. However, this may only be needed rarely and may not be a frequently used function. We have therefore revised the text and made it a recommendation rather than a requirement.

19.5 Recommendation: The system should have the capability for entering annotations for display. A means should be available to distinct annotations from other data.


Some of these may not be applicable to all ORs e.g. range rings not used on an SMR. Perhaps this could be a recommendation.

We agree that some of these may not be applicable to all circumstances, however it is impossible for the CAA to write the context and applicable system for each requirement. Most requirements are written generically and applicable to most scenarios, and it is expected that the specific context is understood by the reader CAP 670 is aimed at. For example, labelling can only be shown where labelling is used. The existing requirement will be amended as follows:

‘The following elements shall be available for display as applicable:’


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The purpose and meaning of this requirement is unclear. Agree with the comment. The text will be changed as follows:

21.2 Where surveillance data from multiple surveillance sources (e.g. SSR/MLAT/combined/non combined) are available, the sources from which data to be displayed shall be available as a selectable function.

The controller must be able to select the sources (where the data is available from multiple sources for the same volume of airspace) from which they prefer the surveillance data to be displayed as suitable to the situation.


Display of Met data should be part of an OR. A regulation is not necessary.

Agreed. The requirement has been deleted.


It would not be normal to display both plots and tracks. There seem to be a misunderstanding in the way in which XXXXX have interpreted this requirement. Tracks can display trail dot history for the track, but trail dots are not similar to displaying individual position symbols.

Nevertheless, on reflection requirements 21.6 to 21.10 will be deleted since we felt that these requirements are more to do with the user requirement rather than safety related requirements.


This is an OR issue. There is no need for a requirement. See the response to comment no. 94.


We believe you would struggle to find a display system as slow as this! It is not a helpful recommendation anymore.

Agreed. The recommendation will be deleted.


The maps are OR specific. For example they would not be on an A-SMGCS.

Please see the response to comment no. 90. The text will be amended to read:

35.8 The map presented shall have specific graphic representation for the following entities as applicable:


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450m would be a large error for an SMR map. XXXXX comment is true for an SMR map or any maps used for surface surveillance applications such as A-SMGCS or for an SMR used as part of an SMGCS.

However, the CAA believes the 450 m accuracy requirement is still a reasonable value for approach services and en-route services. The existing requirement is modified and retained for such services, and a new requirement is introduced for surface surveillance applications. The revised text is as follows:

39.3 On displays used for en-route or approach control services for all features, position accuracy shall be within 450 metres (0.25 NM) (699).

39.4 Recommendation: On displays used for surface surveillance, accuracy of all features should be as defined in section 7.3 of Eurocontrol Functional Requirements for A-SMGCS Implementation Level 1.

NOTE: Where this cannot be met the ANSP shall define and justify the accuracy criteria used for the application for which the system is used.


This paragraph could be better summed up as the maps need to be aligned with the surveillance data.

The CAA disagrees with the manner in which XXXXX has summarised this paragraph. Summarising as a high level objective in this way does not capture the point which is highlighted here, which is an error that could happen in the conversion process as a result of using a different system than that used for the original co-ordinate derivation. How is the reader’s attention brought to this specific issue by summarising it this way?

We therefore do not believe summarising this NOTE as per XXXXX’s suggestion is adequate.

99 SUR12 General comment

We have a general concern about the cost of meeting this proposal. It will be expensive for airports to implement. CAA should consider assessing the cost to the industry.

Comment noted. This document has already been through a round of external consultation, and the CAA believes that in order to justify that a system is safe and meets the performance criteria to provide a particular service, the aspects identified in this section need to be evaluated. Some amendments have been made to this section (see comments below). We would consider if XXXXX could be more specific as to which areas in XXXXX’s opinion are unnecessary or unjustifiable.


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This is an unreasonable requirement, or could result in significant cost to XXXXX. 1m.sq is the recognised standard for performance assessment. The rather unhelpful statement, stating “the smallest target likely to operate in the operational environment” is open to massive abuse. Does that mean for XXXXXX we should procure radars capable of seeing aircraft the size of a 737 or bigger, because that is the most likely target in the area. Or should we be testing against something the size of a bird, because they’re quite likely to be in the operational environment too. Who decides what is most likely?

Text will be changed to 1 m2 which is the recognised standard:

5.2 Where, a dedicated test target is used, the target shall have an RCS of approximately 1 m2.


This is not practical. The process utilised by XXXXX utilises a recording of several hours, capturing thousands of aircraft. To assess the approximate size for each one is not practical. The approach we use currently is to evaluate targets which do not perform as per expectation, to determine whether a small RCS was a contributing factor which is a much smaller dataset to evaluate.

By stating this requirement, the CAA is not expecting XXXXX to find out the RCS of all thousands of targets that were recorded as part of Opportunity Traffic analysis. RCS of a target as seen by the radar is a key factor for the target detection. The system must meet be capable of detecting a 1 m2 target at the greatest range operationally required. Hence Pd expressed without knowing what targets were involved does not have much meaning and does not necessarily mean that the system is capable of detecting small targets (1 m2) at longer ranges operationally required. One might record data for several hours, but the judgment as to whether this meets the operational requirement depends on whether the sample of the data captured during this time represents the targets of small sizes (i.e. 1 m2). Of course the larger the data sample, greater confidence can be placed that almost all types of targets in the area were flown during this period. However the CAA writes requirements generic to all ANSPS and not from one ANSP’s perspective.


Who do SRG deem ‘suitable’. What is meant by time of applicability in this particular context?

Comment noted. The text will be revised as follows:

6.3 Where results are assessed by manual observation, assessment shall be performed by competent personnel (e.g. ATCOs or Air Traffic Engineers), and the results shall be logged with time of applicability.

NOTE: Time of applicability may be the time the data item was displayed or a time duration, where the relevant performance parameter being assessed is measured with respect to time. E.g. probability of update or Pd, or delay etc.


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Please see comment for Page 82, Para 5.2 above. Noted. The text will be changed as follows:

11.4 Detection at the edge of coverage shall be confirmed with a target of 1 m2 RCS.


Why is a dedicated flight trial required? What benefit or value does this add?

On reflection, the CAA believes that the latency attributable to the ground based surveillance system is addressed by requirement 14.1, and therefore 14.2 and 14.3 will be deleted.


Formatting note: The second one……should be Para 14.3.

Exactly how would an ANSP test this? There is no practical way of establishing the point when the action in the cockpit took place with any means of accuracy. This should be covered by factory testing using injected test targets. As for the airframe, this should be certificated by the relevant authorities, why would you want to test it as part of a Sensor or SDP evaluation?

On reflection, the CAA believes that the latency attributable to the ground based surveillance system is addressed by requirement 14.1, and therefore 14.2 and 14.3 will be deleted.

However we would like to emphasise that there are many practical ways of time stamping and recording the performance of the data items related to airborne position and other data items for the purposes of performance assessment.

The data elements and performance criteria defined in recent Eurocontrol Surveillance Performance specification (with Eurocontrol intended to be accepted as AMC to the SPI IR) also contains such data items and end-to-end performance checks which cannot be verified by TOP analysis.


Is this truly necessary? Surely a more pragmatic approach is to configure the sensor to its most demanding operational configuration and test that. If it passes in this configuration why test further?

Agree with XXXXX comment. Text will be revised as follows:

The performance assessment shall assess the surveillance sensor in both its normal mode of operation and in its most degraded mode of continuing operation (807).

Recommendation: All modes of operation of the sensor should be verified.

NOTE 1: Such configurations may include multiple PRFs, polarisation settings, interrogation patterns, reduced redundancy etc.

NOTE 2: Such verification may be achieved through a combination of testing and theoretical analysis.

107 NAV01 paragraph 4.3

Where IRVR systems use a combination of centreline and edge lights to determine the light intensity (as Doc9328 Chapter 6, section 6.5), it

The third edition of the ICAO Manual of Runway Visual Range and Reporting Practices was published in 2005. In this document, the ICAO


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would be worth identifying the range of lamp ageing factors valid in the UK for centre line lights.

Visual Aids Panel determined that the appropriate de-rating factor to be applied to centre-line lights, when these are required, would be 50% while a greater proportion (80%) of the edge lights should be used in the calculation of IRVR. Several factors are mentioned in paragraph 6.5.2 of Doc. 9328 and elsewhere in the same document the effects of errors arising from variations in MOR (visibility), runway lighting intensity and the visual threshold of illumination for the landing pilot are assessed. Greatest of these is the latter because this will be influenced by the level of ambient lighting inside the cockpit, by the transmittance of the windscreen and the angle through which the pilot views the runway lights.

108 Part C, Section 2, NAV 01 paragraph 4.3

LHR Airports Ltd welcome the proposal from CAA to raise the 20% peak to be 40% of the average for edge lights used in IRVR calculations.

We understand that the assumed reduction used historically for AGL output by CAA has been very low and has not changed for many years.

This topic is currently being explored by XXXXX to more accurately take account of real-life achieved light output. Furthermore the general change in the industry towards LED lights should also bring about further improvements that need to be recognised.

The CAA welcomes this positive response. The CAA look forward to assisting XXXXX in achieving this objective and to receiving confirmation of the benefits which we believe will be obtained from these proposals.

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