*2.2. Events Considered in the Design of Exercises*

To design the exercises, the first step was to agree on the ATC events to be considered when creating a designed taskload profile that would characterise each exercise. For this purpose, a series of workshops were organised that brought together ATM experts as well as people with previous experience using SkySim.

Within the group of experts, the vision of experienced working controllers was highly valued. On the other hand, researchers with previous experience in the design of simulation exercises and in the development of validations in research projects at the national and European level were included in the working group.

In particular, there were two previous studies that were very useful for defining the final ATC events. On the one hand, at the national level, UPM had previous experience working with the Spanish Aviation Safety Agency.

On the other hand, the events considered in the SESAR AUTOPACE project were also of great interest [20].

The results of the AUTOPACE project provide a better understanding of how cognition and automation coexist, thus supporting new strategies for training and interface design [21]. Although the objectives are not aligned with those of the present line of research, the events defined in this project have been considered as a reference, as has the definition of difficulty in the design of the exercises.

Figure 2 shows, in schematic format, the activities that were identified as key ATC tasks (shaded in blue), the designed ATC events associated with each of them (shaded in green), and the base score for each of the events (rectangles with a white background).

The first aspect that was defined was the key activities carried out by ATCOs in nominal traffic situations. The result can be seen in the six blue rectangles shown in Figure 2, including the identification of an aircraft, the takeover/handover process, the identification of a conflict and its resolution, and, finally, the monitoring of the traffic present in the sector. On the basis of these activities, at least one event associated with each of them was defined. The twelve events considered can be seen in the green rectangles in the figure above. For each event, an average duration and a base score were defined.

Eleven of the events have an absolute value associated with the event. The monitoring event is the only one that is relative. It is associated per minute with each of the aircraft within the sector at a given time.

In defining the twelve events, complexity factors aligned with those identified by other authors have been considered. Specifically, the authors of [22] conducted a Principal Component Analysis (PCA) on 24 complexity factors defined in the literature to reduce them. The final result was a set of eight complexity factors. Several of these factors have been considered when defining the events listed in Figure 2, in particular, aircraft count, aircraft vertical transitioning, and conflict sensitivity. In this line of research, the complexity factor of aircraft count has been considered by defining three scenarios of traffic density that condition the base values of taskload. Similarly, in the case of conflicts, the contribution

of aircraft climbing or descending has been taken into account by giving conflicts where one or both aircraft are changing their flight level a higher taskload value than conflicts where aircraft are at cruise level.

**Figure 2.** Identification of the key activities carried out by ATCOs (blue rectangles) and the ATC events associated with them (green rectangles). In total, twelve ATC events form the basis of the simulations in the experiment conducted.

Air traffic control is a service task whose duty is to prevent conflicts between aircraft [23]. The events associated with conflicts were discussed in detail. It was decided that conflicts should be categorised according to the state in which the aircraft were: in cruise flight or climbing or descending. When two aircraft are on the same trajectory and one of them starts to approach the other, until the separation minima are infringed, an overtaking event occurs.

ATCOs are required to ensure that minimum separation standards are complied with at all times in terms of horizontal and vertical separation between aircraft [24]. Regarding the level of automation of the platform, the configuration used in this experiment is very similar to the so-called attention-guided mode in [25]. In this configuration, conflict detection is automatically performed by the simulator. However, the ATCO retains the role of controlling the aircraft and is not assisted in resolving the conflict. In the context of this experiment, a conflict is defined as a situation where the minima of 5.0 NM in the horizontal plane and 1000 ft in the vertical plane are infringed.

In the simulator's conflict detection tool, the detection threshold in the horizontal plane is set to 7.9 NM. This allows ATCOs to receive information in advance of a conflict situation occurring. The conflict detection tool helps them identify which aircraft are involved in the conflict situation, how close they will be at the closest point of approach (CPA), and the time until this point is reached. However, the decision-making process to resolve the conflict remains in the hands of the ATCO, without guidance. In short, conflict detection is automated on the simulation platform, but resolution is not.

Although there are many factors that can increase the complexity of an event for a controller, traffic density is one of the key factors that increases perceived workload [26].

To account for this contribution, the base score of each event increases as the number of simultaneous aircraft in the sector increases. For this purpose, three traffic density scenarios were defined: low (less than five aircraft), medium (between five and nine aircraft), and high (more than ten aircraft).

Additional information on the definition of events and the assignment of taskload values can be found in [9]. This reference also includes a table that compares the basic characteristics of the four exercises used in this study, including the number of aircraft in each exercise, the number of events, or the sector in which the simulations were conducted.
