A nacelle comprising a fixed structure with a fixed cowling and a cowling movable in translation between closed and open positions, to open an opening between a duct and the exterior. A blocking door is rotatably movable on the movable cowling between a stowed position and a deployed position. A deployment system comprises an arm with a first end articulated on the blocking door and a second end that bears a stop, a slider fixed to the arm, a linear guide system is fixed on the fixed structure and guides the slide, and a cam. The stop is configured to lie against the cam when the movable cowling reaches an intermediate position from the closed position and to be guided by the cam to drive the rotation of the arm about the slider when the movable cowling moves from the intermediate position to an open position.