An onboard access control system to an information system onboard an aircraft, for communication from the open domain to the avionics domain, the open end avionics domains being connected to each other through a single-directional link from the avionics domain to the open domain. The system includes: a security device including: access switches controlling access to the avionics and open domains, a controller, a module for acquisition putting data into buffer memory and transmission to the avionics domain, a data control module, an acquisition module from the open domain and putting into buffer memory, and an operator's authentication mechanism.