Surveillance Applications Policy – Review Policy on Radar Monitoring

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Surveillance Applications Policy – Review Policy on Radar Monitoring

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

WP No. 92

Surveillance Applications Policy – Review Policy on Radar Monitoring

Presented by TOC

Summary

Radar monitoring is a controller skill based around the most common form of electronic surveillance in use – radar. This skill is practiced by what remains the most integral part of the ATC system – the controller. Increasing pressure by airspace users for greater efficiency is pushing the introduction of new technologies and accompanying procedures which place routes and aircraft closer together to achieve the efficiency goal. Radar monitoring is cited in many of these procedures as a mitigating factor. There is a concern that the controller’s ability to perform their role may be adversely affected, if there is a capacity increase in combination with a reduction in spacing or separation standards. This paper looks firstly at the meaning of the term radar monitoring – as there appears to be uncertainty as to what the term actually means. It then looks at the current IFATCA policy in relation to current applications and other mitigating factors such as monitoring tools. It considers if separation standards are being reduced and the appropriateness of the current policy with regards to the application or R-NAV based procedures.

Introduction

1.1. This paper stems from the concern raised by the Technical and Operations Committee (TOC) that radar monitoring is being increasingly used in conjunction with the implementation of new technologies as mitigation for procedures with criteria below the current separation standards. As a result capacity increase is occurring, increasing controller workload. TOC is also concerned as to what impact this increase may be having on the controller’s ability to perform their role.

1.2. Subsequent discussion has also highlighted ambiguity as to what radar monitoring is by definition. TOC is of the opinion that it is important to establish what radar monitoring means in application.

1.3. The purpose of this paper is to establish a clear definition of radar monitoring, assess its use and finally to review IFATCA Policy.

Discussion

2.1. IFATCA Policy for radar monitoring is broken into two parts as follows:

“Arrival/Departure Phase

Radar monitoring should not be used as the primary means of providing separation between traffic patterns where aircraft are on their own navigation.

Radar monitoring should not be used as the means of providing separation with obstacles (terrain clearance) where aircraft are on their own navigation and below the Minimum Radar Vector Altitude (MRVA). Any escape procedure should provide adequate terrain clearance.

En-Route Phase

Separation standards should not be reduced below those that would otherwise be required purely because of the use of radar monitoring.

Any introduction of Precision RNAV routes should ensure that these routes are spaced at such a distance from each other that the required separation minima are not likely to be infringed if an aircraft on one of the routes deviates from its cleared path.”

 

This policy’s design was influenced by the introduction of:

  • Independent parallel approaches and Precision Runway Monitoring (PRM)
  • Precision Area Navigation (RNAV) and Required Navigational Performance (RNP)

2.2. Radar monitoring Definition

2.2.1 Firstly, it is important to establish what is meant by the words used in the term Radar Monitoring. The definitions below are provided via the Oxford Dictionary.

Radar • noun a system for detecting the presence, direction, and speed of aircraft, ships, etc., by sending out pulses of radio waves which are reflected back off the object.

— ORIGIN from radio detection and ranging.

This definition is obviously based on the operation of primary radar. None the less the essence of its operation is applicable to secondary radar types as well.

Monitor • verb keep under observation, especially so as to regulate, record, or control.

— ORIGIN from Latin monere ‘warn’.

2.2.3 ICAO defines radar monitoring as:

RADAR MONITORING: the use of radar for the purpose of providing aircraft with information and advice relative to significant deviations from nominal flight path, including deviations from the terms of their air traffic control clearances.

2.2.4 IFATCA has no stand alone definition for radar monitoring but refers to the ICAO definition in relation to its current policy.

2.2.5 The ICAO definition indicates a process that is perhaps not as proactive as the literal translation (there is no mention of control) however in both cases monitoring is indicated as a precursor to a more positive action i.e. regulating, recording, control or the provision of information and advice.

2.2.6 It would be fair to say that in application radar monitoring is used more as in the Oxford definition. It is a process carried out to facilitate the application of regulation and control when those positive actions are required.

2.2.7 That is to say monitoring in itself does not affect an aircraft flight path or resolve a conflict. If one of two aircraft on parallel tracks begins to deviate from its flight path no amount of monitoring only will resolve the conflict. The same can be said for an aircraft that deviates on an instrument approach and its proximity to terrain. Radar monitoring is merely a combination of a type of information display and a basic controller skill – deviation/conflict detection.

2.2.8 ICAO PANS-ATM Doc 4444 Chapter 8.6.6.1 adds weight to this with regards to navigation assistance.

An identified aircraft observed to deviate significantly from its intended route or designated holding pattern shall be advised accordingly. Appropriate action shall also be taken if, in the opinion of the controller, such deviation is likely to affect the service being provided.

2.2.9 Again the process of observation (monitoring) is separated from the more proactive appropriate action required when service will be affected.

2.2.10 The questions then raised are – when is monitoring applied and does monitoring cease when those more positive actions have been put into effect?

2.2.11 Radar monitoring is a skill applied by controllers even when no known traffic is displayed at his or her position. The controller must still monitor the screen for any itinerant aircraft that may display or scheduled traffic when they become airborne or enter the airspace. It is something done from the moment the controller assumes the position. But does it cease when the more positive action of control is carried out?

2.2.12 ICAO PANS-ATM Doc 4444 cites radar monitoring as one of the eight key functions of the use of radar in an air traffic service under Chapter 8.7.1:

g) maintain radar monitoring of air traffic;

Note – Where tolerances regarding such matters as adherence to track, speed or time have been prescribed by the appropriate ATS authority, deviations are not considered significant until such tolerances are exceeded.

This highlights its overall application to all radar services.

2.2.13 The ICAO definition of radar monitoring also provides an answer to this:

– information and advice relative to significant deviations from nominal flight path, including deviations from the terms of their air traffic control clearances.

2.2.13 The last part of the above sentence would indicate that this is an ongoing process. If an initial deviation is recognised and control action taken then this will most likely include a revision to the air traffic control clearance such as “turn left 20 degrees” or “descend to FL 150” . Monitoring must continue to ensure that the aircraft is conforming with the revised clearance. Thus the process is on going.

2.2.14 This also agrees with the previously mentioned statement regarding navigation assistance under ICAO PANS-ATM Doc 4444 8.6.6.1 (see para 2.2.8).

2.2.15 Further confirmation of its overall and continuing nature is provided by IFALPA PANS-ATM Chapter 8 X 1.1 with regards to the utilisation of radar:

a) to monitor traffic so as to assure controllers that clearances are being maintained;

2.2.16 We now have a clear understanding of what radar monitoring is –

A continuous process of observation carried out via a radar display, to facilitate the application of regulation and control.

2.2.17 To confirm this interpretation definitions of the proactive terms are included:

Regulate • verb 1 control or maintain the rate or speed of (a machine or process). 2 control or supervise by means of rules and regulations.

Control • noun 1 the power to influence people’s behavior or the course of events. 2 the restriction of an activity or phenomenon. 3 a means of limiting or regulating something. • verb (controlled, controlling) 1 have control or command of. 2 limit or regulate.

2.2.18 It is important to note in the revised understanding the inclusion of there being a radar display.

2.2.19 The reason for this is to delineate radar monitoring from overall conformance monitoring. Conformance monitoring can be conducted in both the procedural and radar environments. In fact it may be fair to say radar monitoring is merely conformance monitoring with the aid of radar.

2.2.20  At this stage, it is also important to highlight the link radar monitoring has with surveillance. The IFATCA Manual provides the following definition:

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

 

2.2.21  Radar monitoring uses radar – which is a form of independent surveillance.

2.2.22  Currently, diversification of surveillance methods is taking place e.g. Automatic Dependent Surveillance – Broadcast (ADS-B) and Multilateration. Concurrently ICAO is reviewing its documents with the intention of making them more applicable to the multiple surveillance forms available. Generic terms that encompass the skills that may be applied regardless of how traffic is surveilled is an example. Radar monitoring is a definition that may fall under this affect.

2.2.23  Many of the findings and definitions derived from this paper could have application in any IFATCA policy or definitions that may need be created or amended to remain applicable as a result of change as described in 2.2.18.


2.3. Primary Tool

2.3.1 Radar monitoring is specifically cited as a mitigating factor in:

  • Independent parallel approaches to Closely Spaced Parallel Runways (CSPR)

2.3.2  Radar monitoring is cited as applicable in the following by higher policy statements or implied by statements of action within the procedure:

  • Approaches to single or parallel runways below 2500ft
  • Dependent approaches
  • RNAV/RNP route and parallel route spacing procedures
  • RNAV/RNP approach procedures

2.3.3  In all these procedures once established on the route or approach navigation resides with the pilot. The controller has no other tool to use but radar monitoring in the first instance to check conformance.

2.3.4  Once deviation is detected or alerted the controller will then move to more positive action and instruction to either retain the required spacing for the procedure or establish separation if an infringement takes place.

2.3.5  This concept impacts on the current policy. To reiterate the affected part:

Arrival/Departure Phase

Radar monitoring should not be used as the primary means of providing separation between traffic patterns where aircraft are on their own navigation.

 

2.3.6  Based on the definition in 2.2.16 and the procedures cited above this requirement is difficult to fulfill.

2.3.7  Going beyond this to the more general application of radar monitoring the same can be said. From the moment a controller takes over a position they monitor the airspace via the radar display presentation of it. All other radar control action stems from this primary task.

2.3.8  From the arguments put forward in 2.3.6 and 2.3.7 it is proposed the current policy is amended.


2.4. Separation and spacing

2.4.1  In the approach environment there are several procedures using radar monitoring that do not conform to the minimum terminal radar separation. These all pertain to parallel runway operations and relate to the spacing required between aircraft on the two approach paths.

2.4.2  Dependent and closely spaced independent parallel approaches require the controller to either maintain or monitor a required spacing. If that spacing is degraded then the controller must take action to re-establish radar separation. This is an important delineation and supported by documents such as the ICAO Manual on Simultaneous Operations on parallel or near-parallel Instrument Runways (SOIR) Doc 9643 section 2.2.2.1 of which highlights the lack of separation criteria for such operations.

2.4.3  Such procedures do increase the capacity of those locations that they are applied in increasing the through put in adverse weather conditions towards the visual conditions level. (On average approximately 1/3 increase above the original adverse weather levels)

2.4.4  Some of the procedures mitigate the increased workload by providing automated monitoring assistance e.g. Precision Runway Monitoring (PRM) and/or dedicating positions to the role of monitoring such approaches e.g. independent parallel approaches to CSPR require one monitoring controller for each approach path.

2.4.5  Some current and proposed reductions in approach spacing do not provide for greater controller monitoring assistance e.g. reduced track segregation for parallel runways below 2500ft centre line spacing or dependent approaches with segregation set at 1.5 NM.

2.4.6  The increase in capacity, in combination with the increased workload of the controller because of the additional monitoring tasks, is an area of concern to IFATCA.

2.4.7  It might be the case, that States are devising and trialing new procedures to accommodate the existing infrastructure at airports. The experience gained from these trials is used to influence ICAO standards. IFATCA’s concern is that this encourages other States to apply such trial standards at locations with further reductions in criteria to suit their own environment. An example of this is the application of independent approaches to CSPR at Frankfurt, Germany, where a 2.5 NM spacing is used between aircraft on the same approach as compare to adjacent approaches as defied in the ICAO criteria.

2.4.8  En-Route and approach RNAV/RNP route design and approach/departure procedures have the potential to have a major impact on radar monitoring.

2.4.9  Eurocontrol studies have indicated that when fully applied, RNAV/RNP routes will potentially result in longer periods of uninterrupted monitoring and less proactive control such as vectoring.

2.4.10  However, full implementation is still some time off and controllers face many risks in the intervening transitional period of mixed mode operations. Methods of accurately and easily conveying aircraft equipage and routing requirements must provide the controller with ease of use.

2.4.11  There is and will continue to be pressure to reduce route spacing and even separation standards in the en-route and approach environments based on the accuracy of RNAV/RNP aircraft navigation systems.

2.4.12  En-Route, as of yet, there has not been a reduction in separation standards. Parallel route spacing is being reduced and Eurocontrol research indicates the closer that it is brought towards the separation criteria the greater the number of controller interventions.

2.4.13  During the review of IFATCA Policy it was noted that the term “separation standards” has been used when referring to the required distance between routes. It is therefore recommended that the term “route spacing” replaces “separation standards” in these instances.

2.4.14  There is case history to support reduction. The application of Reduced Vertical Separation Minimum (RVSM) based on the increased accuracy of aircraft altimetry systems is the best example. IFATCA should not be adverse to such initiatives provided they do not compromise overall safety.

2.4.15  There is a strong case for the requirement of applicable and accurate monitoring tools with such procedures.


2.5. Terrain clearance

2.5.1  There is still some ambiguity as to the responsibility for terrain separation for:

  • Independent parallel approaches to CSPR break out procedures
  • RNAV/RNP approaches and departures and aircraft deviation from the procedure and controller response.

2.5.2  With regards to independent parallel approaches, it is the responsibility of the State to design the procedure so that a breakout instruction can be carried out at any time by the controller down to the minimum of 400ft above threshold elevation and safely allow the flight to achieve the minimum radar vectoring altitude with regards to terrain. ICAO PANS-OPS Doc 8168 Volume II Part iii Attachment S provides guidance for states.

2.5.3  Guidance is required for the controller to outline the response actions required for deviation in the case of non-precision pilot interpreted approaches and RNAV/RNP departure procedures.

2.5.4  Because of the ambiguity indicated it would be prudent to amend the current policy to reflect where responsibility lies for ensuring the safety of procedures that may rely on controller intervention in the event of aircraft navigation error below the Minimum Radar Vectoring Altitude (MRVA).


2.6. Monitoring tools

2.6.1  Monitoring tools provide the controller with the greatest level of assistance at the moment. Their use is specifically highlighted for Closely Spaced Independent Parallel Approaches. Additionally ICAO guidance material cites such tools for consideration by states when initiating plans for reducing route spacing.

2.6.2  Bringing parallel routes or approaches closer together increases the risk of placing aircraft in close proximity in the event of an aircraft deviation, blunder or system error. Eurocontrol studies indicate that closer spacing increases the level of controller intervention whether by cockpit application error or controller perception of deviation.

2.6.3  In many cases route spacing is being reduced in environments, such as terminal airspace, without the provision of adequate monitoring aids. An example of this was the recent application of R-NAV routes in the Brisbane area of Australia without a monitoring tool that could alert controllers (as the tools parameters were set to large values to stop nuisance alerting). This can be particularly dangerous for parallel route structures that include turns over fly by or fly over points.

2.6.4  States must set criteria for route and approach spacing below which adequate automated monitoring assistance is required.

2.6.5  Such monitoring tools should be two stage operating in much the same way as the controller display required by independent parallel approaches. That is a primary alert indicating a deviation from route and a secondary indicating penetration of a route protection area or approach buffer zone.

2.6.6  IFATCA radar monitoring Policy should include a requirement for adequate automated monitoring tools as required by the environment in which radar monitoring is used.

2.6.7  Route design must provide adequate spacing to accommodate deviation, detection and resolution.

2.6.8  IFATCA Policy supports this:

Any introduction of Precision RNAV routes should ensure that these routes are spaced at such a distance from each other that the required separation minima are not likely to be infringed if an aircraft on one of the routes deviates from its cleared path.

 

2.6.9 Additionally Policy should provide support for the use of monitoring tools to assist the controller.


2.7 Airborne tools

2.7.1  There is evidence to suggest that Traffic Collision Avoidance Systems (TCAS) could impact on the controller’s ability to monitor effectively with regards to closely spaced routes and some approach applications. Eurocontrol ACAS bulletins have provided several examples of mis-interpretation and action by pilots based on Traffic Advisory (TA) information provided by such systems. FAA guidance material regarding the application of Simultaneous Offset Instrument Approaches (SOIA) highlights the possibility of Resolution Advisory (RA) alerts and their pre-eminence over controller instruction.

2.7.2  Airborne Separation Assistance Systems (ASAS) will potentially have a major impact on the controller’s monitoring role. The systems use of Cockpit Display of Traffic Information (CDTI) tools may result in the sharing of the monitoring function. Incorrect application of this information by crew similar to that outlined in 2.7.1 is possible.

2.7.3  In its more advanced applications, ASAS could see the responsibility for the maintaining of separation pass to the pilot. This could result in pilot response to onboard monitoring systems and result in reduced controller intervention. Controlling will become more strategic. Some studies have indicated that this scenario could result in relinquishing of the controllers requirement to monitor specific aircraft once separation instruction has been passed to the pilot. This of course would rely on reliable on board systems and procedures and controller confidence in the system.


2.8 Approach versus En-Route

2.8.1  Many of the issues that affect radar monitoring in the approach environment are shared en-route. These include:

  • The reduction in route or track spacing
  • Decreasing application of positive action because of aircraft navigational accuracy and route design
  • Mixed mode operations and varying standards for en-route and approach classification
  • Onboard application of TCAS information

2.8.2  In both environments when aircraft are under their own navigation it is radar monitoring that becomes the controller’s initial means of deviation/conflict detection.

2.8.3  R-NAV/RNP errors, failings and advantages are applicable to both environments. Examples include:

  • Human input error
  • The reference system used in RNAV applications e.g. FMS, INS, GPS
  • Varying levels of equipage and onboard conformance monitoring creating mixed mode operations

2.8.4  The application of appropriate monitoring tools would be beneficial in both environments. This is particularly true when closely spaced route structures are being devised or approach procedures that intend to use criteria below the approach separation minima.

2.8.5  From the arguments and examples presented in 2.8 it is possible to combine the current arrival/departure and en-route phase policies into one.

Conclusions

3.1.  Pressure to increase the capacity of the ATS system continues to build.

3.2.  The controller will continue to be seen as the most critical part of the ATC system for the foreseeable future and will continue to be during the transitory period that the industry is going through.

3.3.  Radar monitoring is the primary function that radar controllers conduct and is continuous in nature. All other radar controller actions with regards to radar traffic stem from this function.

3.4.  Clearer understanding of what defines radar monitoring is required. As this working paper places IFATCA in a position where it does not agree with the ICAO definition the federation should have its own definition of the function.

3.5.  Many of the issues that affect approach monitoring are shared by en-route monitoring. Combination of the separate policy statements for the arrival/departure phase and en-route is possible.

3.6.  With regards to terrain clearance, there are several approach procedures that leave the controller potentially exposed if required to intervene with positive control actions when aircraft deviation is observed. States need to clearly mitigate such ambiguity.

3.7.  In the approach environment there are several procedures that do not use the minimum terminal radar separation. There are also some States applying and proposing standards that go even lower than those defined in ICAO documents – many without any further assistance to the controller in his or her monitoring role.

3.8.  En-Route and approach route spacing will continue to evolve around extracting greater capacity generally by closer spaced routes. This has the potential to increase controller workload through greater intervention.

3.9.  During the review of IFATCA Policy it was noted that the term “separation standards” has been used when referring to the required distance between route. It is therefore recommended that the term “route spacing” replaces “separation standards” in these instances

3.10.  RNAV/RNP accuracy and procedure design will, longer term, reduce the amount of positive controller intervention.

3.11.  Accurate and applicable monitoring tools are the best available aid for the controller at present. Such monitoring tools could include:

  • Trajectory prediction functions,
  • A Route deviation alert,
  • A Penetration alert for when aircraft enters the protected airspace buffer between such routes.

3.12.  Airborne Separation Assistance Systems (ASAS) will potentially have a major impact on the controller’s monitoring role. This will be longer term however possibly over the next 10 – 15 years.

Recommendations

It is recommended that;

4.1.  The following definition of radar monitoring:

A continuous process of observation carried out via a radar display, to facilitate the application of regulation and control.

is included in the IFATCA Manual on page 3 2 3 9.

4.2.  IFATCA Policy on page 3 2 3 9 of the IFATCA Manual:

Radar monitoring should not be used as the primary means of providing separation between traffic patterns where aircraft are on their own navigation.

Radar monitoring should not be used as the means of providing separation with obstacles (terrain clearance) where aircraft are on their own navigation and below the Minimum Radar Vector Altitude (MRVA). Any escape procedure should provide adequate terrain clearance.

Separation standards should not be reduced below those that would otherwise be required purely because of the use of radar monitoring.

Any introduction of Precision RNAV routes should ensure that these routes are spaced at such a distance from each other that the required separation minima are not likely to be infringed if an aircraft on one of the routes deviates from its cleared path.

is deleted.

4.3. IFATCA Policy is:

Route spacing standards should not be reduced below those that would otherwise be required purely because of the use of radar monitoring.

Radar monitoring should not be used as the means of providing separation with obstacles (terrain clearance) where aircraft are on their own navigation and below the Minimum Radar Vector Altitude (MRVA). Any escape procedure shall provide adequate terrain clearance from the point the aircraft is below the MRVA to the lowest defined altitude at which any such pocedure can be initiated. States are required to assure this.

Any introduction of RNAV/RNP routes that are spaced below the current non RNAV/RNP route spacing, with the intention to increase capacity, must be accompanied by the introduction of accurate automated monitoring assistance for the controller.

Any introduction of Precision RNAV/RNP routes should ensure that controllers can, upon identification or notification of a deviation, carry out the necessary action so that the required separation minima is not likely to be infringed.

and is included in the IFATCA Manual on page 3 2 3 9.

References

Oxford Dictionary.

ICAO PANS-ATM Doc 4444.

IFALPA PANS-ATM.

Working paper B 5.10.

Last Update: September 29, 2020  

April 13, 2020   262   Jean-Francois Lepage    2007    

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