The declared capacity calculations often require approval from national and international safety agencies. Therefore, it is necessary to use a well-defined and validated methodology, in which all stakeholders, such as ANSPs, airport managers, air traffic controllers, etc., can form an expert committee to offer their expertise and propose final figures for capacity declaration.

Creating a methodology starts with defining the concept of capacity. According to EUROCONTROL, Air Traffic Control (ATC) capacity refers to ‘the maximum number of aircraft that can enter a Control Area in a given period of time, while maintaining an acceptable level of ATC Workload’.

A methodology for calculating the operational capacity of various air traffic control services, including airport tower positions, approach and en-route sectors, can be created by directly applying air traffic controller workload calculations to a fast-time simulation.

Organizations such as ICAO and EUROCONTROL recognize that the human factor plays a significant role in air traffic capacity limitations. EUROCONTROL’s own documentation, published in 2003, presents a more nuanced perspective, noting that “workload is a construct […] that cannot be seen directly, but must be inferred from what can be seen or measured.” For this reason, methodologies based on workload calculations require careful implementation.

Establishing the Baseline for Capacity Calculation

Considering all these definitions and assumptions, the baseline of any capacity calculation methodology can be established:

1. Firstly, real data on ATC activity should be collected and characterized with the help of operational experts in the control position.
2. Secondly, the scenario to be analyzed needs to be modeled to be able to perform a fast-time simulation.
3. As a result of this simulation, flight events that can be correlated with control events will be obtained, thus allowing ATC activity to be gathered.
4. It will then be possible to calculate the workload generated by the activity that a controller must perform to manage the flights. Numerous studies and theories of human factors allow the calculation of the workload from the activity performed, i.e. Wickens’ Multiple Resource Theory.
5. Finally, all the metrics and complexity thresholds can be validated based on hourly workload to guarantee an efficient, safe, and sustainable ATC operation.

The Importance of Fast-Time Simulation in Capacity Studies

Fast-time simulations offer a significant advantage by providing a realistic representation of airport and airspace operations. This facilitates the assessment of proposed modifications without disrupting actual operations and saving time and resources. As a result, fast-time simulations have become a crucial tool for ANSPs and airports in capacity studies. 

This process revolves around two main events: the fast-time simulation modeling to obtain all flight events, and the workload model to translate said events into measurable calculations. The combination of these two parts makes it possible to obtain capacity per position as a function of the control service provided. 

Inputs Needed for Effective Capacity Modeling

A fast-time simulation tool, such as AirTOP is designed to reproduce aircraft movements by generating flight events. These events can be used to infer the associated control tasks.

For a methodology to be effective, the tool requires specific inputs:

• Airspace sectorization
• Historic traffic data or forecast
• Restrictions related to aircraft movements on the ground, such as pushback, taxiing routes, parking position rules, runway exit selection or queue management
• Letter of agreements
• Arrival and departure procedures, etc.

To obtain as many scenarios as possible, the traffic samples used can start with the usual demand of the airport or airspace under study. These samples can then be cloned up to saturation levels to reach high workload situations.

How Workload is Quantified and Analyzed

For workload analysis, the methodology relies on different theories or processes, usually based on the use of cognitive channels. The purpose of these cognitive models is to evaluate the resources required for ATC activities, to determine whether this demand stays within human factor limits, and to not put operations at risk.

To quantify the level of controller activity, each set of control events within a given time interval will be linked to a value that estimates ATC workload. Some workload calculation methods consider that equal events, such as assuming a flight, require the same time and effort from the controller. Others, however, account for the unique characteristics of each flight, recognizing that some inbound events are easier while others are more complex. Therefore, the cognitive effect corresponding to each calculation is applied, factoring in the weights assigned to the channels used, as well as the interference that occurs between these cognitive channels. As a result, each action of the controller has a different weight depending on the resources demanded.

The events performed by a controller can and will occur separately and consecutively or, on the contrary, simultaneously. Simultaneous tasks increase workload as it reduces the execution time and places greater demands on resources. The latter type of workload measurement method allows a task-level description and considers the non-linear relationship between workload and occupancy time. It also considers the complexity of actions, and how decision-making is harder if there are several decisions to take at the same time

By adding all these events, tasks and actions over time, and considering the interference between them, an instantaneous workload can be visualized. This data can then be used to create workload vs aircraft per hour graphs and compare several scenarios. For example, scenarios with new taxiways or updated instructions for aircraft crossing the runway.

Turning Simulation Data into Actionable Insights

AirTOP is a powerful tool for modeling the behavior of airspace and airports, allowing users to assess the impact of changes in infrastructure and operations. It generates detailed information about the flight events required for an aircraft to operate within the airport environment. By analyzing the output data from the simulation, a schematic of the activities performed by control personnel can be built, as an aircraft’s status only changes with controller authorization.

The simulation output provides a complete record of all the phases the aircraft has gone through within the analyzed area, which are then translated into ATC actions, each assigned to different workload values. Once the scenario is simulated, it becomes possible to study the workload distribution across different areas of responsibility or determine how to deploy the most appropriate positions according to the expected traffic movements. It is also possible to analyze what benefits can be expected when joining or deploying certain positions.