Abstract : The Air Traffic Control (ATC) environment is complex and safety-critical; operators work in dynamic situations and must make high-risk decisions under stress and temporal pressure. Whilst exchanging information with the aircrafts under their responsibility via radio, operators must also be alert to the occurrence of auditory alarms, such as the collision avoidance alert or danger area infringement warning. In addition, auditory warnings are increasingly integrated within ATC workstations. The high perceptual load involved in ATC means that controllers’ attention must be shared between several subtasks, with few or no remaining attentional capacity for processing information that is not related directly to the focal task. In this kind of situation, the likelihood of a controller failing to become aware of an auditory alarm, i.e. inattentional deafness, is high. Characterizing physiological symptoms associated with inattentional deafness would enable online detection of the phenomenon in safety-critical situations (nuclear power station supervision, piloting or air traffic control). We designed an ecological ATC thanks to the simulation environment called the “LABY” microworld. Twenty participants were required to guide one (low cognitive load) or two planes (high cognitive load) around a given route, while dealing with visual notifications relating to peripheral aircrafts. During the task, participants were played either standard tones which they were told to ignore, or deviant tones (“the alarm”, probability = 0.20) which they were told to report (20 alarms per scenario). We hypothesized that the detection rate of auditory alarms will decrease with cognitive workload. In order to explore this possibility, Behavioral results showed that 28.8% of alarms were not reported when guiding one plane, and up to 46.2% when guiding two planes (high load). The cognitive load increase led to a reduced visual notification detection rate, but the performance to guiding the central aircrafts was maintained, as well as the reaction times to report auditory alarms when perceived. This high rate of inattentional deafness is essential to further physiological studies on alarm omission in aeronautics, such as ERP or eye movement analysis. Potential applications are related to the integrative online detection and prevention of alarm omission, and the online measurement of workload in ecological situation.