Introduction

1.1. During the 2004 IFATCA conference, a definition was accepted for Controller Tools. This definition was written to provide guidance to Member Associations (MAs) who may be asked to assess the use of enhanced functionalities or increasing levels of automation.

1.2. The purpose of this paper is to investigate Route Conformance Monitoring Systems (RCMS) and its associated alerts, the Route Deviation Alert (RDA) and the Estimated Time Over Deviation Alert (ETODA), and recommend appropriate definitions. Presently IFATCA does not have definitions or policy for these tools.

1.3. For the purpose of this paper, TOC considered a route to be a two dimensional path, i.e. lateral and longitudinal. Lateral monitoring is based on cross track deviation and longitudinal monitoring is based on along track deviation.

Discussion

2.1. A Route Conformance Monitoring System (RCMS) is a function of an Automated Air Traffic Management System that scrutinizes the positions of aircraft to detect when they divert from their expected routes. Position information is received from various forms of surveillance (the surveillance position, i.e. from radar, ADS-B or ADS-C).The processed position or track is then displayed to the controller on the air situation display and the RCMS compares the surveillance position with the expected position from the route of the Flight Data Record (FDR). The processor has logic to decide if the surveillance position is laterally displaced outside the route using pre-defined route conformance tolerances. If so, the RCMS will respond in various ways; often by suspending other processing as well as alerting the controller by displaying a Route Deviation Alert (RDA). The route conformance tolerances vary and often depend on the type of airspace (i.e. amount of traffic, proximity of traffic to other routes or restricted use airspace, etc.) and also on what other interfaces are associated with the system (i.e. flow management tools).

2.2. The functionality of the RCMS is described above, however it has different titles in different countries. It is called a Route Adherence Monitor (in Australia) and IFATCA has referred to it in the past as a Route Deviation Monitor. We are classifying this tool by describing its functionality and will refer to it as an RCMS to reduce confusion.

2.3. An RCMS is a tool that assists controllers in meeting the objectives of ATS but it does not replace the need for the controller’s decision making processes. It doesn’t dictate a course of action and is therefore a Controller Tool as per IFATCA policy:

2.4. In a procedural control environment, longitudinal displacements (i.e. if an aircraft will be earlier or later at a particular waypoint) can also be monitored. Where a pilot estimate (Estimated Time Over: ETO) is entered into the Flight Data Processing System (FDPS) and it differs from a previous pilot estimate or system estimate by a pre-determined tolerance, an alert can be provided to the controller. This alert also has different titles in different countries but we will refer to it as an Estimated Time Over Deviation Alert (ETODA). Processing is normally unaffected by an ETODA however the controller should check the new pilot estimate and attempt to resolve the discrepancy.

2.5. Indirectly, the RCMS functionality could assist controllers by providing an RDA on aircraft deviating towards sensitive areas or into conflict with a busy route. The RCMS is still considered to be a Controller Tool and not a Safety Net, as other tools should warn controllers during these events.

2.6. Present IFATCA policy supports the use of these tools:

2.7. The HMI of the RCMS is vastly different throughout different systems. Some systems don’t provide notification to the controller whereas others will present a deviation to the controller as a Route Deviation Alert (RDA) using visual and/or aural indications. Others will alert the controller indirectly through another tool; for example certain flight plan conflict probes are designed to provide an alert to the controller when the RCMS indicates an aircraft’s position is outside tolerances (even though no alert is received directly from the RCMS). Other tools rely on output from the RCMS to function correctly; for example some Medium Term Conflict Detection tools (MTCD) require an FDR to be within tolerances before it is included in its conflict search. Some systems will continue normal processing after an RDA while others will suspend certain processing to prevent the use of incorrect information.

2.8. The regularity with which the position information is processed by the FDPS depends on the type of airspace and the airspace user. If the FDPS utilised a surveillance position that isn’t on the FDR route but is within the RCMS tolerances, it will (normally) project the position onto the route and use this projected position for certain processing. As a result, there can be a difference between where the aircraft is and where the FDPS thinks the aircraft is. If the surveillance position subsequently moves outside the RCMS tolerances, the flight data system may suspend certain processing and will often provide a warning to the controller when this has happened. This is because there is a possibility that strip posting and automatic hand-offs as well as other functionalities may be incorrect. Calculations using times or estimates may also be suspended. Certain other events can also cause the deferral of RCMS processing; for example: aircraft being held; or aircraft who have left the relevant airspace or have had their FDR manually suspended by the controller. Processing will normally recommence after the route has been updated to reflect where the aircraft is going; thus cancelling the RDA.

2.9. The airborne equivalent to an RCMS is a Track Deviation Indicator which presents the aircraft’s displacement from the route knowledge held in the Flight Management System onto the Navigation Display. There is no aural warning, only the visual presentation in the cockpit.

2.10. For the Automated ATS System to function, changes to the aircraft’s route, level and estimates for positions are required. This is achieved either automatically, using Automatic Position Reports (APRs), or manually by the controller using an estimate, reroute or level update function within the HMI. For example, if an aircraft diverts from its planned route due to vectoring, track changing or weather deviations, the FDPS information would be incorrect and the facility must exist to update the flight data system so the FDR for a flight matches the aircrafts route, level and speeds. This is often called a re-route.

2.11. APRs provide a regular interface between the surveillance position and the RCMS processor. The update rate for automatic position reporting is generally predetermined however can often be changed by the controller either for a particular flight or for the workstation. This rate would be higher (three or four times a minute) during climb and descent, in areas where vectoring is commonplace or where other processing is involved (i.e. flow management processing tools). This is to provide accurate estimates as soon as an aircraft tracking returns to a known point on the route. The RCMS allows APRs to trigger calculation of the aircraft’s profile, estimates for position, flight levels and the list of crossed sectors using the mode C or reported altitude and the surveillance position.

2.12. The controller must be adequately trained in what processing is suspended during an RDA, how an RDA influences the system integrity as well as how to respond to an ETODA. When the Automated ATS System is degraded, clearly defined operational procedures must exist. Regular refresher training for operations for degraded modes must be provided. To avoid distraction, nuisance and false alerts must be kept to an absolute minimum.

Conclusions

3.1. An RCMS is a function of an Automated ATS System that monitors the position of an aircraft to detect when it deviates from its route. An RCMS compares aircraft trajectory data from various forms of surveillance with known points on the system route for an aircraft and then calculates if the aircraft position falls outside pre-defined parameters. When this occurs, certain processing can be suspended and an alert is often sent to the controller. An RCMS is considered to be a Controller Tool.

3.2. An RDA is an alert provided to a controller to notify that an aircraft’s position is laterally displaced outside the tolerances defined within the RCMS, and that certain processing may be suspended.

3.3. An ETODA is an alert provided to a controller to notify that the system or pilot estimate is significantly different from a the previous estimate.

3.4. Adequate training must be provided prior to the introduction of such tools. Regular refresher training for operations for degraded modes must be provided. Suitable operational procedures must exist for operations during degraded modes.

3.5. An RCMS is not designed to replace traditional methods of track monitoring but is intended to be used as a Controller Tool to assist in monitoring conformance.

Recommendations

It is recommended that;

4.1. A Route Conformance Monitoring System be defined as:

A Route Conformance Monitoring System (RCMS) is a function of an Automated ATS System that monitors the position of an aircraft to detect when it deviates from its route. An RCMS is considered to be a Controller Tool.

and be included in the IFATCA Manual page 3 2 1 20.

4.2. A Route Deviation Alert be defined as:

A Route Deviation Alert (RDA) is an alert provided to a controller to notify that an aircraft’s position is laterally displaced outside the tolerances defined within the RCMS, and that certain processing may be suspended.

and be included in the IFATCA Manual page 3 2 1 20.

4.3. An Estimated Time Over Deviation Alert be defined as:

An Estimated Time Over Deviation Alert (ETODA) is an alert provided to a controller to notify that the system or pilot estimate is significantly different from a previous estimate.

and be included in the IFATCA Manual page 3 2 1 20.

References

ICAO Doc 4444.

WP 89 – Hong Kong 2004.

Professional and Technical Manual of IFATCA (2004).

IFATCA Manual (2004).