Abstract : During their initial and on-the-job training, air traffic controllers communicate with human operators called pseudo-pilots who act as pilots for several simulated aircraft. With the expected increase in air traffic, a significantly higher number of aircraft will be handled during the simulations. The existing tools and working methods of the pseudo-pilots do not allow them to handle more traffic without increasing the number of operators. The increase in the number of pseudo-pilots induces problems of cost, logistics and collaboration (distribution of traffic and radio frequency congestion). This article describes the design process and improvement of a pseudo-pilot HMI which led us to a radical change of both the visualization and the interaction. This user centered process aims to optimize visualization, effectiveness of interaction and the level of realism of the simulations. We also integrated in a seamless and robust way voice recognition in the visualization.