Apparatus for obstructing air flow through an aperture in an aircraft wing where a movable anti-icing duct extends through the aperture are disclosed. An exemplary apparatus comprises a base member (40) configured to be secured to the duct and a first seal member (42) configured to obstruct air flow through the aperture. The first seal member comprises a proximal portion (42A) connected to the base member and a distal portion (42B) configured to movably contact an inner surface of a skin of the wing. The use of such apparatus may reduce the amount of leakage flow from the high pressure lower wing surface to the low pressure upper wing surface through the aperture and thereby reduce the loss of lift associated with such leakage flow.