4D Trajectories for Air Traffic Management. Concept of Operations and Implementations

One of the main missions of Air Traffic Management (ATM) is to efficiently separate aircraft sharing the same airspace.

Trajectories, which describe their movement in space, play an essential role in this task, enabling :

• maintain an adequate safety distance between aircraft;

• provide a concise description of the flight intentions of each airspace user (AU);

• facilitate the management of potential conflicts between several aircraft ;

• calculate possible traffic overloads in overhead sectors;

• establish a mental representation shared by the various ATM players.

In order to model, represent and process these trajectories, various automated systems have been implemented, both by airlines (e.g. flight planning algorithms) and by control organizations (e.g. dynamic sectorization or regulation algorithms). To cope with the significant increase in traffic and its growing complexity due to the emergence of new aircraft types, major ATM systems modernization programs (such as SESAR in Europe) have been launched, alongside new automated control systems (such as 4-FLIGHT ).

4D trajectories, including the aircraft's current and past position, as well as its flight intentions, are a major element common to all these programs and systems. However, at the time of their deployment, it is essential to ask in-depth questions about the notion of trajectory. Do all players really share the same definition of trajectory? What does 4D actually mean? What technological building blocks are needed, both on the ground and on board aircraft? What's the difference between a 4D trajectory and a 4D contract? Are 4D trajectories also suitable for managing other types of traffic?

The aim of this article is to provide precise answers to these questions, by defining the various terms and concepts and exploring the traffic management systems of yesterday, today and tomorrow. How can 4D trajectories be implemented in practice? Will they make it possible, with reasonable investment, to meet the ATM challenges of the years ahead, in particular...