A pylon for attachment of a gas turbine engine to a wing of an aircraft has a trailing edge which is rearward of the trailing edge of the core fairing and the trailing edge of the fan nacelle. The pylon has two laterally-spaced side faces which extend in the rearward direction of the engine to end at the trailing edge of the pylon. Each side face has a bottom edge which extends in a rearward direction of the engine from the core fairing to the bottom end of the trailing edge of the pylon. The bottom edges merge such that the bottom edges form a single bottom edge. The pylon is intended to exert control on the bypass flow of a gas turbine engine. Other pylons are also provided which can also exert such control.