Abstract : This article deals with the introduction of partial automation in the En-Route air traffic control working position. More precisely, it presents an experiment whose objective is to evaluate the generated impact on air traffic controllers by the use of a more automated environment, including a conflict aid services system (conflict detector and solver). This impact is evaluated through the assessment of air traffic controllers' mental workload. In this experiment, the evaluation of mental workload is carried out mainly through psychophysiological parameters, especially ocular data. This assessment is compared with subjective evaluation collected by questionnaire and assessment scale, and also with performance indicators analysis focused on communications between controllers and pilots. Results achieved show that automated system proposed in the case of the SESAR project (W.P.4.7.2) seems to be promising because it generates a decrease of mental workload felt in comparison with a non-automated situation.