Abstract: The main concepts of flight separation safety assessment are present: flight separation, separation minima, conflict, airmiss, and collision. Then the flight separation safety assessments are addressed in detail from six main models: REICH model, intersecting rout model, probability model, stochastic analysis model, EVENT model and RASRAM model, and then the application scope, merits and drawbacks of each model are analyzed. The results show that the main key problems of safety assessment of flight separation are the conditional limit of the model, the reasonable intent and safety evaluation. Furthermore the tendencies of the research in the future are put forward: the flight separation safety assessment based on communication, navigation, surveillance (CNS) performance, the avoidance system how to reduce the collision risk, and human factors how to influence the collision risk.

Key words: air traffic management, flight separation, collision risk, safety assessment