Preventing mid-air collisions despite increasing traffic and the introduction of new airspace users, such as drones.
Mid-air collisions have occurred since the beginning of aviation. The investigations in the aftermath of each collision have prompted R&D to introduce or enhance systems and procedures that increase aviation safety. Following several decades of research and development in the USA, a first Airborne Collision Avoidance System (ACAS) was installed on some commercial airliners in the early 1990’s.
Then, in 2002 a mid-air collision happened over Überlingen (Germany) between a commercial aircraft and a cargo jet, both equipped with ACAS. All 69 passengers and crew members were lost. The resulting investigation identified among the main causes, ambiguities in the operational ACAS procedures for pilots and a limitation in the version of the ACAS involved. It triggered research and improvement across all these fronts, coordinated in Europe by EUROCAE and EUROCONTROL and involving stakeholders from system suppliers, air navigation service providers, airlines, pilots, regulators and more.
This tragic event illustrates the wide ranging and complex nature of ACAS, requiring studies not only into systems themselves but also their operational environment, procedures, training and use.
Today, the integration of drones into the same airspace in which aircraft currently operate, create new situations, which could potentially lead to close encounters, or even mid-air collisions. The performance and the characteristics of drones are different to airplanes, so it is not possible to equip them with the same ACAS. This has led to the development of a new ACAS, dedicated to drones.
A key principle for all ACAS systems is that they have to be as independent as possible from the other aircraft equipment for the triggering of the alerts. Nevertheless, it is possible that some advanced aircraft functions could improve ACAS performance through a connection to the autopilot, without affecting the ACAS itself.
ACAS is embedded in aviation operations today, which means that whenever a new operation is conceived, its compatibility with ACAS must be assessed and validated. With all industry players aiming to improve flight efficiency and airspace capacity, operational change is inevitable. Expertise in ACAS is as important today as it was when Egis first began working on it, 27 years ago.