Self-separation

Aircraft Self-separation is the capability of an aircraft maintaining acceptably safe separation from other aircraft without following instructions or guidance from a referee agent for this purpose, such as air traffic control. In its simplest forms, it can be described by the concept of see and avoid, in the case of human-piloted aircraft, or sense and avoid, in the case of non-human piloted aircraft (such as UAVs). However, because of several factors such as weather, instrument flight rules and air traffic complexity, the Self-separation capability involves other elements and aspects such as rules of the air, communication technologies and protocols, air traffic management and others.

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 nowadays flights is 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, 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.

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