specifically the actuator 60 comprises a hollow body 61 inside which a translatable rod 62 is housed the hollow body 61 is attached at its upstream end to the front frame structure 4 while the rod 62 is attached at its free downstream end to the nozzle flap 50 said rod 62 thereby passing through the upstream end of the moving cowl 30 and optionally the rear frame structure 40 to be fastened on the nozzle flap 50 alternatively it is also possible to consider the following opposite solution a threaded rod fixed in translation and rotating and a hollow tube connected on the one hand to the flaps and on the other hand to the threaded rod by means of a nut to manage the pivoting of the nozzle flap 50 and the translational movement of the moving cowl 30 the rod 62 of the actuator 60 is movable between a first position called idle position shown in fig1 and 2 in which the rod 62 controls the moving cowl 30 in its closing position and the nozzle flap 50 in its closed position a second position called open position of the nozzle flap 50 illustrated in fig3 and 4 in which the rod 62 is retracted inside the hollow body 61 relative to the first position said rod 62 keeping the moving cowl 30 in its closed position and commanding the pivoting of the nozzle flap 50 toward its open position by going from the first to the second position and a third position called open position of the moving cowl 30 illustrated.