The invention relates to a fly-by-wire system which comprises: three-stage piloting control, each stage including a control computer suitable for determining the positions of the stick, and a monitoring computer capable of verifying all the pre-determined positions of the stick; three-stage control-surface position calculation, each stage including a control computer suitable for calculating the control-surface positions from encoded positions of the stick, and a monitoring computer capable of verifying all the calculated control-surface positions; a single unidirectional communication link connecting the control computer of the first piloting control stage to the control computer of the first control-surface position calculation stage; a single unidirectional communication link connecting the control computer of the second piloting control stage to the control computer of the second control-surface position calculation stage; and a single unidirectional communication link connecting the control computer of the third piloting control stage to the control computer of the third control-surface position calculation stage.