A conflict is an event in which two or more aircraft experience a loss of minimum separation. This does not in itself suggest that the aircraft are at any risk of collision. However, the separation minima are set for risk mitigation and therefore it is central to a controller's job to prevent this situation from occurring. Conflicts are detected by data assistants, who report them to the actual controllers; the data assistants suggest how to solve the conflict, but the controller is not obligated to follow the suggested instructions. A conflict occurs when the distance between aircraft in flight violates a defining criterion, usually considered as 5 nautical miles (9 km) of horizontal and/or of vertical separation. These distances define an aircraft's protected zone, a volume of airspace surrounding the aircraft which should not be infringed upon by any other aircraft.Kuchar, J. K., Yang, L. C. “A Review of Conflict Detection and Resolution Modeling Methods.” IEEE Transactions on Intelligent Transportation Systems, Vol. 1, No. 4 2000: 179–80.
