Conflict avoidance (CA) is an essential aspect of Air Traffic Management (ATM). One criterion for conflict is that the aircraft is under-protected zone (PZ), which is there should be 1,000 ft distance exist between two planes as a mini-vertical distance. Conflict Detection and Resolution (CDR) was solved by using three maneuvers, namely velocity, altitude, and flight direction. The main problem of the CDR is to provide optimal solutions without interfering with the time flight that has been given. In this work, the Velocity, Turn and Altitude Change (VTAC) model will be implemented as a CDR approach and a solution basis to avoid conflicts between aircraft. The VT AC model provides three solutions to avoid planes from conflicts, which are changing altitude, turn, and velocity. The purpose of the VTAC model is to minimize changes in altitude, turn and velocity so that the aircraft still flies according to its flight time. The output of the VTAC model is the altitude, turn angle, and velocity of the plane which does not conflict with other aircraft. Moreover, we also put consideration on cumulonimbus cloud to be avoided by a plane in our simulation. By employing a well-known heuristic Particle Swarm Optimization (PSO) method, the conducted correctness test of shows that all of the potential conflicts are able to be avoided.