Turbofan engine having a longitudinal axis and comprising a motor and a nacelle that surrounds the motor and has a fan casing, wherein a duct for a bypass stream is delimited between the nacelle and the motor and in which an air stream circulates in a flow direction, said nacelle having: - a fixed structure fixed to the fan casing, - a movable assembly having a movable cowl and a slider, the movable cowl being fixed to the slider, the slider being movable in translation on the fixed structure in a translation direction between an advanced position, in which the slider is positioned such that the movable cowl is moved close to the fan casing, and a retracted position, in which the slider is positioned such that the movable cowl is moved away from the fan casing so as to define, between them, an open window between the duct and the outside of the nacelle, - a plurality of blades, each having a first end that is mounted so as to be able to rotate on the slider about an axis of rotation and wherein the blades are angularly offset from one to the next about the longitudinal axis, wherein each blade is able to move between a stowed position, in which the blade is outside the duct, and a deployed position, in which the blade is across the duct, - a set of actuators that move the slider between the advanced position and the retracted position and vice versa, and - a manoeuvring system intended for moving each blade from the stowed position to the deployed position and vice versa, wherein the manoeuvring system has: - for each blade, a shaft that is mounted so as to be able to rotate on the slider about an axis of rotation, and to which the blade is fixed, - for each shaft, a balance beam (414a-c) fixed to the shaft and having a first end and a second end, which are disposed on either side of said shaft, - for a first balance beam, a second balance beam and a third balance beam that are angularly consecutive, two connecting rods (408a-b), wherein the first connecting rod has two ends, one of which is mounted articulated on the second end of the first balance beam and the other of which is mounted articulated on the second end of the second balance beam, and wherein the second connecting rod has two ends, one of which is mounted articulated on the first end of the second balance beam and the other of which is mounted articulated on the first end of the third balance beam, and - an actuation system which produces the rotation of one of the balance beams (414a-c) in one direction and in the other. - a fixed structure fixed to the fan casing, - a movable assembly having a movable cowl and a slider, the movable cowl being fixed to the slider, the slider being movable in translation on the fixed structure in a translation direction between an advanced position, in which the slider is positioned such that the movable cowl is moved close to the fan casing, and a retracted position, in which the slider is positioned such that the movable cowl is moved away from the fan casing so as to define, between them, an open window between the duct and the outside of the nacelle, - a plurality of blades, each having a first end that is mounted so as to be able to rotate on the slider about an axis of rotation and wherein the blades are angularly offset from one to the next about the longitudinal axis, wherein each blade is able to move between a stowed position, in which the blade is outside the duct, and a deployed position, in which the blade is across the duct, - a set of actuators that move the slider between the advanced position and the retracted position and vice versa, and - a manoeuvring system intended for moving each blade from the stowed position to the deployed position and vice versa, wherein the manoeuvring system has: - for each blade, a shaft that is mounted so as to be able to rotate on the slider about an axis of rotation, and to which the blade is fixed, - for each shaft, a balance beam (414a-c) fixed to the shaft and having a first end and a second end, which are disposed on either side of said shaft, - for a first balance beam, a second balance beam and a third balance beam that are angularly consecutive, two connecting rods (408a-b), wherein the first connecting rod has two ends, one of which is mounted articulated on the second end of the first balance beam and the other of which is mounted articulated on the second end of the second balance beam, and wherein the second connecting rod has two ends, one of which is mounted articulated on the first end of the second balance beam and the other of which is mounted articulated on the first end of the third balance beam, and - an actuation system which produces the rotation of one of the balance beams (414a-c) in one direction and in the other.