A gas turbine engine includes a core engine casing, a bypass duct and a core engine duct. The gas turbine engine further includes a plurality of flaps pivotally coupled to the core engine casing and arranged circumferentially around a principal rotational axis. Each flap extends from a first casing end and is configured to pivotally rotate relative to core engine casing about a pivot axis between a first position and a second position. In the first position, each flap is disposed in a circumferential direction and is radially disposed between a plurality of outlet guide vanes and a plurality of stator vanes. In the second position, each flap is inclined to the first position and extends at least partially into the bypass duct and the core engine duct.