Turbofan having a longitudinal axis and comprising a motor and a nacelle, surrounding the motor, which comprises a fan casing, wherein a duct for a bypass flow is delimited between the nacelle and the motor and in which a flow of air flows in a direction of flow, said nacelle comprising: - a fixed structure fixed to the fan casing, - a movable assembly having a movable cowl and a slider, the movable cowl being fixed to and downstream of the slider with respect to the direction of flow, the slider being movable in translation on the fixed structure in a direction of translation between an advanced position, in which the slider is positioned such that the movable cowl is close to the fan casing, and a retracted position, in which the slider is positioned such that the movable cowl is away from the fan casing so as to define, therebetween, an open window between the duct and the exterior of the nacelle, - a plurality of blades, each one comprising a first end mounted on the slider so as to be rotatable about an axis of rotation generally parallel to the longitudinal axis, wherein each blade is movable 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 causing the slider to move between the advanced position and the retracted position, and vice versa, and - a manoeuvring system intended to move each blade from the stowed position to the deployed position, and vice versa, characterized in that the set of blades comprises a first stage, which is furthest downstream with respect to the direction of flow, wherein the blades are positioned in one and the same plane perpendicular to the longitudinal axis, one after another around the perimeter of the slider, and in that, in the following stage, which is upstream with respect to the preceding stage in the direction of flow, the blades are positioned in another plane perpendicular to the longitudinal axis and are angularly offset about the longitudinal axis with respect to the blades of the preceding stage, and so on. - a fixed structure fixed to the fan casing, - a movable assembly having a movable cowl and a slider, the movable cowl being fixed to and downstream of the slider with respect to the direction of flow, the slider being movable in translation on the fixed structure in a direction of translation between an advanced position, in which the slider is positioned such that the movable cowl is close to the fan casing, and a retracted position, in which the slider is positioned such that the movable cowl is away from the fan casing so as to define, therebetween, an open window between the duct and the exterior of the nacelle, - a plurality of blades, each one comprising a first end mounted on the slider so as to be rotatable about an axis of rotation generally parallel to the longitudinal axis, wherein each blade is movable 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 causing the slider to move between the advanced position and the retracted position, and vice versa, and - a manoeuvring system intended to move each blade from the stowed position to the deployed position, and vice versa,