Abstract: An air-to-air heat exchanger is provided for a gas turbofan engine to significantly reduce the quantity of cooling air that is presently needed to effectively cool the hot turbine parts. Typically, the turbine is internally cooled with air bled from the compressor which, though cooler than the turbine, has been heated due to the work done on it by the compressor. In accordance with the present invention, the heat exchanger is located internally of the bypass duct to place in heat exchange relationship a captured portion of the relatively cool bypass flow and this warmer compressor bleed air, thereby cooling the turbine coolant and significantly reducing the amount of such coolant required. This results in a decrease in engine specific fuel consumption.