First-come, first-served—the decades-old paradigm for equitable access to airspace—is being challenged as uncrewed aircraft enter the airspace in greater numbers, requiring a new definition of fairness.

The diversity of use cases for uncrewed traffic management (UTM) requires a new approach to prioritizing airspace access, so the Airbus UTM team has partnered with the Massachusetts Institute of Technology (MIT) to develop the concept of a Fairness Engine.

In traditional air traffic management (ATM), Airbus UTM says, the first-come, first-served approach works because today’s flight plans are not deconflicted because flight and the traffic is relative homogeneous. In most UTM systems, however, flight plans are deconflicted when they are requested, resulting in a first-requested, first-served approach to prioritizing airspace access.

But first-requested, first-served becomes increasingly inadequate as uncrewed traffic grows and the types of operation increase and become more varied, Airbus UTM says. The approach can leave operators that cannot file flight plans early, such as on-demand delivery services and air taxis, unfairly disadvantaged, the Airbus unit says.

Because it has a decentralized architecture in which a network of service providers manage traffic based on shared data and common regulation, implementing fairness in the early stages of UTM’s development is critical, says Airbus UTM, and discourages early movers and industry giants from gaming the evolving system.

The Fairness Engine concept has two components: monitoring flight operations by gathering fairness-relevant information from operators and service providers; and automatically applying that information to traffic management conflicts to determine priority in a way that is fair.

“We started by thinking what data is available and what are the metrics we can use to monitor a system that could lead to a notion of fairness and then, from there, how do you manage it?” says Scot Campbell, U.S. head of Airbus UTM.

“Fairness exists in the traditional air traffic management system because there’s this notion of first-come, first-service and of collaborative decision-making,” he says. “[But] a lot of collaborative decision-making is centered around human negotiation and sharing of information, whereas the systems of the future are digital. And the question we ask ourselves is how can we leverage the digital information that is being shared in order to monitor fairness so that it can be managed?”

The monitoring function of the Fairness Engine considers the cost of ATM to the operator measured by the delay they suffer beyond what they would experience if they were the only operator seeking airspace access.

“In UTM there is a service commonly called strategic deconfliction where an operator will share their intent and the system will then look for a conflict. And if there is a conflict, then the operator is going to need to do something to resolve it,” Campbell says.

“One of the things they can do is delay their flight and replan their operation for some time in the future,” he says. The Fairness Engine seeks to identify when an operator filed its intent to the system and if that intent was accepted or a conflict was identified and the operator had to replan.

Measuring that delay is one way to assess the cost. “The system will keep track of how people have operated historically so you’ll know when they have accepted delay and when they haven’t had delay and that could potentially be a factor in the prioritization of flights in the future,” Campbell says.

“The other way it can be done is to have an additional service in UTM that is monitoring things like system demand and that could then provide resolutions based on delay,” he says. As demand for airspace increases, access delays increase, so demand and capacity balancing within UTM would distribute the delay across operators with a sense of fairness.

The first step in Airbus UTM’s vision is to monitor system behavior to identify occurrences of under airspace use. With MIT, the team is working with standards developers, including ASTM International, to ensure that as UTM standards are published they include the level of data logging needed to support the monitoring of fairness, he says.

The next step is prioritization of how flights are authorized based on a calculation of fairness. Initially this function determines priority based on the type of operation–emergency services before passenger and package services, for example.  In the event of a conflict between operations of the same type, the program would apply the fairness metric assigned by the monitoring function based on historic delays to resolve the conflict and determine priority.

Transparency will be important. “The key is that the prioritization rules would be well-known. It’s something that ideally would be a community-based approach,” Campbell says. 

In parallel to working with standards organizations, Airbus UTM has implemented elements of the Fairness Engine as an operational prototype within air navigation service provider Airservices Australia’s Flight Information Management System to support new users of low-altitude airspace. “It is not commercialized, but has gone through a set of operational trials,” he says.