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4D trajectory management: an initial controller perspective |
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A real-time simulation, held in March 2007, investigated 4D trajectory management in an en-route environment. Allowing aircraft to adhere to their preferred 4D trajectories enhanced flight time predictability, but impacted controllers’ tasks. The findings from this simulation and a cockpit simulation held in December 2007 will be used to help refine the 4D trajectory management concept in the context of SESAR.
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The main purpose of this simulation was to conduct a preliminary operational feasibility assessment of the 4D trajectory management concept expressed as a Target Time of Arrival (TTA) in conjunction with the Network Operations Plan (NOP). A secondary aim was to integrate and evaluate the impact of Data Link services on the executive and planning controllers’ roles and tasks (as a follow on to Gate to Gate project).
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With regards to the concept aircraft fly a 4D filed trajectory to achieve a TTA with a timeframe window (up to 2 minutes early and up to 3 minutes late). Hence controllers have to respect the filed 4D trajectories of the aircraft to ensure the aircraft is ‘on-time’ as opposed to expediting traffic through the system. The main aim of 4D trajectory management is to enhance traffic predictability and reduce traffic bunching.
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“Electronic” ATC System; Data link (Controller Pilot data link communication – CPDLC, Controller Access Parameters – CAP, Pilot Preferred Downlink – PPD) were included in the simulation. No advanced tools such as Medium Term Conflict Detection (MTCD) were used.
The en-route airspace chosen was a subset of the current Maastricht Upper Airspace, comprising three measured sectors (Delta, Munster and Ruhr). The route network was based on current route structures. The traffic samples used were taken from live traffic on a busy day in July 2005. The simulation was conducted over a period of four weeks, which comprised two weeks training and two weeks measured exercises, in March 2007. Nine controllers participated in the simulation from AENA, DSNA, ENAV, IAA, ROMATSA and MUAC.
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Objectives of the simulation |
Prior to the simulation several operational options of how the 4D trajectory management concept could be implemented and managed were explored. The option chosen was considered the most feasible from an operational controller perspective: the controller would facilitate the aircraft to adhere to its 4D trajectory in order to achieve its TTA. However, ultimate responsibility to achieve the TTA rested with the aircrew. The main objective of this simulation was to present the concept to controllers and gain preliminary feedback and data. The concept was assessed in terms of usability and suitability, and its impact on the controller (roles, tasks, workload, situation awareness etc), on traffic (predictability, flight efficiency, patterns/complexity) and on safety.
The simulation also assessed the benefits and the limitations of data link services when 75% of aircraft are data link equipped and the impact on executive and planning controller roles and tasks.
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A range of techniques (questionnaires and debriefings) were used to obtain feedback and subjective data from controllers together with system performance data obtained from platform recordings.
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The simulation was divided into two sessions. The first session was an exploratory study to present the concept and gain as much feedback as possible. This first session had three organisations in order to introduce the 4D trajectory management concept to the controllers in a progressive manner. Data link was to be used in all organisations as an alternative to R/T (radio telephony) by the executive in non time critical situations. In addition to normal tasks, the planning controller also had to monitor the executive controller data link communications, to respond to any delegated communication tasks using data link and to transfer out all data link equipped aircraft when exit conditions were met and clear of traffic.
Organisation A: Controllers were instructed to control traffic as today, ensuring a safe, orderly and expeditious flow of traffic i.e. to solve conflicts efficiently, to avoid conflicts by de-conflicting traffic (using direct routes) and to expedite traffic where possible (by issuing direct routes).
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| Figure 1: Flown trajectories (organisation A) |
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Organisation B: Controllers were instructed to adhere to the flight plan route of an aircraft as much as possible. To this end, controllers had to avoid expeditious routings (direct routes) and had to solve conflicts efficiently (but avoiding direct routes as a resolution). After conflict resolution, controllers had to ensure aircraft resumed their flight plan routes as soon as possible.
Organisation C: Controllers were instructed to adhere to the flight plan route of an aircraft and monitor the position of the aircraft in the timeframe window. As a result, they were instructed to avoid expeditious routings, to consider the position of an aircraft in the timeframe window (early / late) when solving a conflict and to resume the flight plan route as soon as possible after conflict resolution.
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| Figure 2: Flown trajectories (organisation C) |
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The second session of the simulation was a more rigorous experimental study, the aim of which was to gain preliminary performance data in order to assess the operational benefits and limitations of the concept (i.e. organisation C) compared to a control organisation (i.e. Organisation A).
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Controllers were generally positive about the concept. However, they reported that they only considered an aircraft’s target time of arrival when they had the time to do so i.e. when workload was not too high.
The requirement to adhere to the flight plan route and TTA was found to affect the controller’s tasks in several ways. The planning controller was unable to use direct routes to solve potential conflicts early and as a result could do less pre-sector planning and preparation. The planning controller had to concentrate on and monitor more what was happening within the sector, supporting the executive controller, identifying and remembering potential conflicts. The executive controller's role was generally unaffected by the concept. However, some changes to tasks were identified, and these changes were also found to be potential safety issues. Direct routes and speed changes were avoided to respect the TTA and as a result the executive controller had fewer options available to resolve potential conflicts. Potential conflicts could not be dealt with early e.g. ‘give a direct and forget’. Instead the executive controller had to continue to monitor any identified potential conflicts until they could be resolved in a way that did not take them off their trajectory for too long. This led to an increase in the amount of monitoring and the process of conflict resolution took longer. Furthermore, when the executive controller acted to resolve the conflict the task became more time pressured and time critical. As a result controllers felt that directs within their own sector should be permitted.
Controllers also had an additional factor to consider when resolving conflicts, i.e. how their actions might affect an aircraft’s TTA, thus adding to the complexity of conflict resolution. Some controllers reported experiencing additional pressure since pilot requests now had greater priority as requests for direct clearances were to facilitate an aircraft in achieving its TTA. Responses from questionnaires indicated that these changes resulted in an increase in the workload experienced by both executive and planning controllers. As a result all controllers felt that the responsibility for ensuring adherence to the TTA should rest with the pilot and not the controllers.
System performance data indicated that although predictability was enhanced (Figure 3) the distance flown by aircraft was greater than when direct routings could be used (Organisation A). Furthermore, requiring aircraft to adhere to the trajectory in the current system was found to increase the complexity of traffic patterns with traffic being more condensed over certain crossing points (Figure 4). The controllers felt this was due to the concept being implemented with the current route structure and sector configuration. For the full potential benefits of 4D trajectory management to be achieved all controllers strongly felt that the current route structure should be examined and possibly modified, and larger sectors respecting traffic flows be introduced.
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| Figure 3: Predictability - Comparison of real and expect flown distance |
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| Figure 4: Bunching at SPY - sector DD |
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With regards to data link, the controllers found it to be a useful tool, as in the Gate to Gate project. However, they experimented less with task sharing than in Gate to Gate and adhered more to the given guidelines. This was probably because the controllers were not so familiar with each other as the controllers in Gate to Gate were.
The findings from this preliminary simulation will be used to help refine the 4D trajectory management concept in the context of SESAR. Future studies to examine route structure and sector configuration to comply with the concept and the impact of the concept on traffic patterns and characteristics will be conducted. A cockpit simulation was conducted in December 2007 to investigate the impact of the concept on pilot roles and tasks. Prototyping sessions are also planned to further develop the requirements for the 4D trajectory management interface, tools and operational procedures. The output of all these planned studies will feed into the Episode III Cycle 1 real time simulation planned for December 2008 as part of SESAR validation.
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This simulation was made in the frame of the EVP programme from DG-TREN, as a follow-on to the Gate To Gate project. The controllers came from AENA (Spain), DSNA (France), ENAV (Italy), IAA (Ireland), ROMATSA (Romania) and MUAC (Maastricht).
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Last validation: 12/02/2008
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