The human factor in air traffic control (ATC) has been the subject of widening discussion as air navigation service providers (ANSPs) increasingly push the boundaries of technology and automation. Recent incidents in the US have reawakened a conversation about the burden on ATC operators, and the factors impacting their performance.

In November 2018, an air traffic controller at McCarran Airport, which serves Las Vegas, was heard slurring her words and giving unclear instructions as pilots continually asked her to repeat herself. Following this, the FAA made a statement saying it was investigating the causes of the incident, and that the controller was no longer employed at the airport.

Air traffic controllers were forced to work without pay as a result of the US Government shutdown. Temporary lay-offs led to some airports being thin on the ground, leading to overtime and cognitive overload for controllers essentially working for free.

“It is a very high-stress job and you need to be on your game at all times,” Mick Devine of the National Air Traffic Controllers Association (NATCA) told NPR. “There is a concern that as this goes on, the human factors aspect of this shutdown will take a toll on the psyche and concentration level of our members.”

With various countries around the world impacted by shortages in air traffic controllers, and demand for air services ever increasing, analysing the human factor in ATC is seemingly more important than ever.

Put emergency procedures in place

Following the Las Vegas incident, the FAA introduced a new policy requiring two controllers to be in an ATC tower for the first 90 minutes of the midnight shift. A NATCA statement said it was “important to remember the outstanding work that is done every day by the thousands of men and women who keep the National Airspace System safe”.

“We are proud of our safety record both in Las Vegas and at every facility, and will continue to work to keep our airspace system the world’s safest,” the statement continued.

National Air Traffic Services head of human performance Neil May is tasked with minimising the impact of human error and enhancing safety in an ATC operation. He says that for UK controllers, training is provided on an annual basis for unusual circumstances and emergencies, so they are well practised in taking over from another controller in an emergency situation should the need arise.

“Controllers work in teams and are continually communicating with each other,” he says. “If the behaviour of a controller was unusual, this would be spotted immediately by one of their colleagues who would raise concerns with the individual, the supervisor and other team members. Assistance would be provided to the incapacitated controller and a team member would immediately take over the role of that controller, ensuring a safe operation.”

Causes of stress in ATC

Pursuing the human factor consists of decreasing the potential of ATC error and enhancing safety. A major aspect of this is analysing sources of stress and streamlining ATC procedures to lessen potential impacts on human performance. According to SKYbrary, the common sources of stress in ATC are related to the operational aspect, such as peaks of traffic load and time deficit; and organisational aspects like shift management and conflicting roles.

“What is stressful for Italians maybe is not stressful if you go to Germany because the context is different, the training is different and so on. There are some events that are stressful for all, but you have specific situations generating stress.”
Stefano Bonelli

SKYbrary acknowledges that errors still occur during periods that may be deemed less stressful; when traffic is light or not notable for its complexity, controllers are required to continually maintain vigilance. The period following a time of very high stress can result in a situation called the lacuna of indecision, when it becomes impossible to take decisive actions.

Stefano Bonelli is a human factors expert working at Italian consultancy Deep Blue. He says that much of the stress placed upon air traffic controllers is dependent on the organisation or culture they work in.

“What is stressful for Italians maybe is not stressful if you go to Germany because the context is different, the training is different and so on,” he says. “There are some events that are stressful for all, but you have specific situations generating stress.”

The role of air traffic controllers is set to change in the future due to the use of highly automated systems. For example, the FAA’s Next Generation Air Transportation System development programme strives to create a future in which air traffic controllers will work with new automation tools, such as the Standard Terminal Automation Replacement System, En Route Automation Modernisation and Data Comm.

“You are changing the role from an active role to a monitoring role,” says Bonelli. “This means that there will be different situations leading to stress.”

Innovative technologies

Funded by the Single European Sky ATM Research project, the STRESS project examined the impact of new technologies on controller performance. The project was conducted by European partners, including the École Nationale de l’Aviation Civile and Eurocontrol, and coordinated by Deep Blue.

Concluded in 2018, the project had a number of outcomes, including “guidelines for the design of innovative technologies that are compatible with human capabilities and limitations”.

However, arguably the most important development of the project is a neurophysiological measurement toolbox that can assess the impact of future ATC scenarios on controllers.

STRESS identified a number of relevant human factors, including attention, mental workload and types of cognitive control on tasks. Using a number of air traffic controllers as test subjects, it collected data that was used to develop specific neurophysiological indicators (for instance, brain activity) for each of these factors. The next step was to measure neurophysiological signals given off by controllers while they participated in a simulated future ATC scenario.

Bonelli says that there are many ways of estimating the impact of a new tool on stress, but they don’t always hit the mark. Questionnaires for controllers may be too subjective, while measuring the level of cortisol in the blood – another stress indicator – is too invasive.

Bonelli adds that if it were distilled into a more practical device, the STRESS technology could be used by ANSPs during demonstrations of new automation procedures. Controllers would be able to objectively show their employers whether new tools and procedures were, in fact, increasing their workload beyond a reasonable limit.

“We spoke with a lot of controllers, and they would like to have these kinds of tools, because now organisations don’t trust them,” Bonelli says.

Bonelli says that feedback had generally been good for the project so far. One extreme worry was that the tool could be used by ANSPs to determine whether or not an employee was too overwhelmed to carry on in their position. However, overall controllers saw it as a good tool for proving their point.

Next steps for the project will involve increasing the scope of the technology to measure other factors such as fatigue and situational awareness.

NextGen technologies

The FAA’s plan to modernise US aviation, the Next Generation Air Transportation System (NextGen), is leading to the introduction of a range of new technologies that impact air traffic management. Intended for use by aircraft in most US airspace by 2020, the Automatic Dependent Surveillance Broadcast uses satellite technology to transmit information, resulting in increased accuracy. New computer systems – the Standard Terminal Automation Replacement System and En Route Automation Modernisation – are now in use at many ATC facilities. Decision support systems for air traffic management are reportedly saving between two and five minutes per departure at 20 airports, while Data Comm allows for written messages as well as radio, reducing the likelihood of misunderstandings.