: This paper describes a collision avoidance problem of aircraft. In a conventional avoidance problem, there is an assumption that target information is certain. However, information may not be always certain in reality, and handling of uncertain information has not been discussed. Therefore, new control law is proposed to deal with uncertain information and to get correct information. The uncertainty depending on position, which is defined in the inertial or relative coordinate system, is dealt with in this paper. To cover each coordinate system, proposed control law is applied to 'corner problem' and 'in-fog problem', respectively. Several elements are defined in order to express uncertainty of target information. Simulation results show that the severe avoidance by conventional law is improved and to be obtained satisfactory performance by dealing with uncertain information.