An adjustable orifice for use in an aircraft air conditioning system includes a first orifice element which has an orifice frame as well as a first orifice area. When the orifice is assembled at a duct, the first orifice area of the first orifice element leaves open a part of a cross section of the duct. The orifice also includes a second orifice element with a second orifice area. When the orifice is assembled at the duct, the second orifice area of the second orifice element leaves open a part of the cross section of the duct. The second orifice element is rotatable about an axis, so that the second orifice area is rotatable relative to the first orifice area in order to set a desired flow cross section in the duct.