The access system has a hinge pin that is offset with respect to the primary articulated joint (14). The step plate being linked to the door by one drive component that is connected to the door by a third articulated joint (16) and to the step plate by a fourth articulated joint (17). The pins of first, second, third and fourth articulated joints are parallel to one another and arranged so as to form the four summits of a parallelogram deformable between an open position and a closed position of the door.
