A gas turbine engine comprising: an inner cowl ; an annular air-oil cooler ; and a fan air diverter , the fan air diverter comprising: a nozzle flap disposed circumferentially about the inner cowl and coaxially adjacent to the annular air-oil cooler , the nozzle flap being pivotally coupled to the inner cowl and selectively movable relative to the annular air-oil cooler between an open position and a closed position; and an actuation system assembly operatively coupling the nozzle flap to the inner cowl , the actuation system assembly being configured to actuate the nozzle flap between the open position and the closed position; characterised by : a plurality of cooling fins of the annular air-oil cooler extending into a fan duct and nozzle and into a path of the fan airflow ; wherein the nozzle flap is axially positioned in the fore of the annular air-oil cooler , the nozzle flap having a leading edge that is pivotally hinged to a surface of the inner cowl and a trailing edge that is movable between the open position and the closed position relative to an inlet of the annular air-oil cooler . an inner cowl ; an annular air-oil cooler ; and a fan air diverter , the fan air diverter comprising: a nozzle flap disposed circumferentially about the inner cowl and coaxially adjacent to the annular air-oil cooler , the nozzle flap being pivotally coupled to the inner cowl and selectively movable relative to the annular air-oil cooler between an open position and a closed position; and an actuation system assembly operatively coupling the nozzle flap to the inner cowl , the actuation system assembly being configured to actuate the nozzle flap between the open position and the closed position; characterised by : a plurality of cooling fins of the annular air-oil cooler extending into a fan duct and nozzle and into a path of the fan airflow ; wherein the nozzle flap is axially positioned in the fore of the annular air-oil cooler , the nozzle flap having a leading edge that is pivotally hinged to a surface of the inner cowl and a trailing edge that is movable between the open position and the closed position relative to an inlet of the annular air-oil cooler . a nozzle flap disposed circumferentially about the inner cowl and coaxially adjacent to the annular air-oil cooler , the nozzle flap being pivotally coupled to the inner cowl and selectively movable relative to the annular air-oil cooler between an open position and a closed position; and an actuation system assembly operatively coupling the nozzle flap to the inner cowl , the actuation system assembly being configured to actuate the nozzle flap between the open position and the closed position; characterised by : a plurality of cooling fins of the annular air-oil cooler extending into a fan duct and nozzle and into a path of the fan airflow ; wherein the nozzle flap is axially positioned in the fore of the annular air-oil cooler , the nozzle flap having a leading edge that is pivotally hinged to a surface of the inner cowl and a trailing edge that is movable between the open position and the closed position relative to an inlet of the annular air-oil cooler . a plurality of cooling fins of the annular air-oil cooler extending into a fan duct and nozzle and into a path of the fan airflow ; wherein the nozzle flap is axially positioned in the fore of the annular air-oil cooler , the nozzle flap having a leading edge that is pivotally hinged to a surface of the inner cowl and a trailing edge that is movable between the open position and the closed position relative to an inlet of the annular air-oil cooler . <EOS>