An engine pylon has a primary structure fastened between an engine and an aircraft wing and a cowling system having a front set of fixed cowls, a rear cowl, a displacement system having a first structure as one with the rear cowl and having a first slide mechanism, and a second structure fastened to a fixed structure of the wing and having second slide mechanism. The slide mechanisms cooperate so as to realize a sliding connection and to move the rear cowl in translation from an advanced position to a retracted position. An immobilizing system locks the rear cowl in the advanced position.