Abstract: In an aircraft wing having a landing flap, a driven, flap mounting carriage being guided in rails, a tri-parted, aerodynamically contoured cover structure for the rails constructed for avoiding any formation of gaps unfavorable for aerodynamic flow over and around the wing, and having an upstream cover body, a middle cover body and a downstream cover body, the upstream body is secured to the wing; the middle body is hinged to the upstream body; the downstream body is hinged to the carriage by means of a first hinge connected to the downstream body, a biparted rocker connected to the first hinge, a second hinge connects the rocker to the carriage; the rocker has its two parts controlled by means of two rods each connected to these hinges; a downstream portion of the downstream body is connected to the flap by means of a rod hinged respectively to the downstream body and the flap, the downstream body is telescoped into the middle body and they are interconnected through pins extending from sides of the middle b