Turbofan engine having a longitudinal axis and comprising an engine and a nacelle surrounding the engine which comprises a fan casing, in which a stream of bypass air is delimited between the nacelle and the engine and in which a flow of air circulates in a direction of flow, said nacelle comprising: - a fixed structure fixed to the fan casing, - a mobile assembly having a mobile cowl and a runner, the mobile cowl being fixed to the runner, the runner being translationally mobile on the fixed structure in a direction of translation between an advanced position in which the runner is positioned so that the mobile cowl is close to the fan casing and a back-off position in which the runner is positioned so that the mobile cowl is away from the fan casing to define between them a window that is open between the stream and the outside of the nacelle, - a plurality of blades, each comprising a first end mounted to be rotationally mobile on the runner about an axis of rotation and in which the blades are angularly offset step-by-step about the longitudinal axis, in which each blade is mobile between a retracted position in which the blade is outside of the stream and a deployed position in which the blade is across the stream, - a set of actuators ensuring the displacement of the runner between the advanced position and the back-off position, and vice versa, and - a manoeuvring system intended to displace each blade from the retracted position to the deployed position at the same time as the runner is displaced from the advanced position to the back-off position and vice versa, the manoeuvring system comprises, for each blade, a shaft mounted to be rotationally mobile on the runner about an axis of rotation, and to which the blade is fixed, characterized in that the manoeuvring system comprises: - for each blade, a toothed segment fixed to the shaft and coaxial with the axis of rotation, - a toothed arc coaxial with the longitudinal axis, mounted to be rotationally mobile on the runner about the longitudinal axis, in which the teeth of the toothed arc mesh with the teeth of each toothed segment, - a slip mounted to be translationally mobile on the runner in a plane at right angles to the longitudinal axis between a first position corresponding to the retracted position and a second position corresponding to the deployed position, - a connecting rod mounted articulated between the slip and the toothed arc, - a rib integral to the fixed structure, and - a guiding U integral to the slip and which straddles the rib, in which the rib has an appropriate form for displacing the guiding U and therefore the slip from the first position to the second position when the runner is displaced from the advanced position to the back-off position, and vice versa. - a fixed structure fixed to the fan casing, - a mobile assembly having a mobile cowl and a runner, the mobile cowl being fixed to the runner, the runner being translationally mobile on the fixed structure in a direction of translation between an advanced position in which the runner is positioned so that the mobile cowl is close to the fan casing and a back-off position in which the runner is positioned so that the mobile cowl is away from the fan casing to define between them a window that is open between the stream and the outside of the nacelle, - a plurality of blades, each comprising a first end mounted to be rotationally mobile on the runner about an axis of rotation and in which the blades are angularly offset step-by-step about the longitudinal axis, in which each blade is mobile between a retracted position in which the blade is outside of the stream and a deployed position in which the blade is across the stream, - a set of actuators ensuring the displacement of the runner between the advanced position and the back-off position, and vice versa, and - a manoeuvring system intended to displace each blade from the retracted position to the deployed position at the same time as the runner is displaced from the advanced position to the back-off position and vice versa, the manoeuvring system comprises, for each blade, a shaft mounted to be rotationally mobile on the runner about an axis of rotation, and to which the blade is fixed, characterized in that the manoeuvring system comprises: - for each blade, a toothed segment fixed to the shaft and coaxial with the axis of rotation, - a toothed arc coaxial with the longitudinal axis, mounted to be rotationally mobile on the runner about the longitudinal axis, in which the teeth of the toothed arc mesh with the teeth of each toothed segment, - a slip mounted to be translationally mobile on the runner in a plane at right angles to the longitudinal axis between a first position corresponding to the retracted position and a second position corresponding to the deployed position, - a connecting rod mounted articulated between the slip and the toothed arc, - a rib integral to the fixed structure, and - a guiding U integral to the slip and which straddles the rib, in which the rib has an appropriate form for displacing the guiding U and therefore the slip from the first position to the second position when the runner is displaced from the advanced position to the back-off position, and vice versa.