The invention relates to a flap (10) for air channels provided with a multi-flow conduit arranged downstream with respect to said flap, airflows (45, 46) being limited by flow guiding elements (56, 57), and thereby separated from each other. According to said invention, the axis of rotation (11) of the flap is arranged on the edge, the flap being transversally projected with respect to the axis and divided into two flap segments which are arranged one after another. Each flap segment is provided with at least one sealing device (14) for airtight seating against a passage opening.