The arrangement comprises a fan by-pass duct located within the nacelle and having an inlet and an outlet. The outlet is generally oriented substantially radially and at an intermediary location along the nacelle. The nacelle has an aft section with an initially convex and substantially outwardly extending surface adjacent to the outlet of the fan by-pass duct. The surface of the aft section decreases in curvature and becomes concave towards a rear end of the engine.