A flight control system of an aircraft including a first processing unit, a second processing unit, communication means configured to establish a first two-way digital link and as second two-way digital link between the first processing unit and the second processing unit. The second link is redundant with the first link, and the first link and second link are likely to be active concomitantly. The system further includes backup communication means enabling data exchanges between the first processing unit and the second processing unit in the case of a failure in the first link and second link. The backup communication means includes an array of sensors or actuators and/or a secure onboard network for the avionics.