In this paper, we show how genetic algorithms can be used to solve en-route aircraft conflict automatically to increase Air Traffic Control capacity in high density areas. The ATC _ background and the model are presented. The complexity of the problem is then discussed. The author then justifies the choice of GAs. After a brief description of genetic algorithms, the author describes the improvements that were used for solving the conflict resolution problem. Several numerical applications are then given justifying the choices that were made and illustrating the interest of the research. Next steps of this work are discussed in the conclusion.