A Krueger, or leading edge flap, deployable from a lower aerodynamic surface of an aircraft main wing element so as to form a slot between the Krueger and the main wing element when deployed, the deployed Krueger having a leading edge, a trailing edge and upper and lower aerodynamic surfaces extending between the leading edge and the trailing edge, and a flow deflector which provides an effectively divergent flap profile thickness in the downstream direction at or adjacent the Krueger trailing edge so as to direct airflow away from the lower aerodynamic surface of the deployed Krueger towards an upper aerodynamic surface of the main wing element. Also, aircraft wing assembly including a main wing element and the Krueger.