A cover door that includes a frame having a wall and an upper aperture extending at the end of the wall, and a lid covering at least one portion of the upper aperture and movable relatively to the frame so as to clear the upper aperture. The lid is attached to the wall through a hinge-forming area. The hinge-forming area has at least one central hinge connecting a central portion of the lid to the frame, and at least one side hinge connecting a side portion of the lid to the frame. The side hinge has a greater length than the length of the central hinge.