Pilots of modern aircraft cannot rely only on visual abilities and piloting skills to maintain acceptably safe
separation from other aircraft, thus a considerable proportion of contemporary flights are performed under
instrument flight rules with the responsibility for
separation belonging to
air traffic control (ATC). However, as the air traffic growth in the end of the 20th century and in the beginning of the 21st is straining the
ATC capacity, and pilot shortages become an ongoing issues, researchers on aviation and air transport are trying to propose operational and technological improvements in order to cope with this strain, one of which is self-separation. Self-separation started being considered as a potentially feasible operational concept within the
Free Flight initiative. Its key technological enabler is
automatic dependent surveillance-broadcast (ADS-B), in which aircraft spontaneously transmit periodic position and state reports, including absolute horizontal position information, which is not used as information source for the pre-existing
Traffic Collision Avoidance System (TCAS). In relation to the current implementations of TCAS, which is intended only for collision avoidance, self-separation requires a leap in processing logic, time anticipation and procedure changes. Its feasibility is dependent on confidence in automation and its co-existence with the human role in the cockpit. Some studies have been conducted to assess this relationship, and the results show that the concept is well acceptable from the pilot point of view without imposing unreasonable workload. An aligned but less radical and more implementable approach was later proposed and named as Distributed Air-Ground Traffic Management (DAG-TM), keeping ATC still with a significant role, but allowing more freedom in en-route airspace. Besides, other relevant aspects in a wider context have been studied in the Mediterranean Free Flight project (MFF) which had, as one of the main conclusions, that self-separation would be overall beneficial, but it should have to be limited to low- or medium-density
airspace. Since the beginning of the association between self-separation and
ADS-B, it has been also associated with another technical concept called Airborne Separation Assistance System (ASAS) which, in short words, performs the core logic of Self-separation and other related applications. With this association, the concept of aircraft Self-separation in the full technological and operational context is more clearly distinguishable from the already cited
see and avoid and
sense and avoid basic concepts. ASAS was an assumption in the MFF project and also in subsequent studies such as the series from Consiglio et al., which went deeper in the
human factor aspects and set the foundations for separating strategic and tactical conflict management processes in self-separation. Other projects provided complementary contributions, such as the Advanced Safe Separation Technologies and Algorithms (ASSTAR), which carried out performance, safety and cost-benefit analyses for ASAS applications, including a limited version of Self-separation, resulting in positive findings. Based on the above-mentioned and other studies, ASAS-based self-separation has been selected as one of the goals to be pursued by major development programs in air traffic management, such as
Single European Sky ATM Research & Development (SESAR) and the U.S. Next Generation Air Transportation System (NextGen), even if limited to certain conditions and airspaces. == Recent developments ==