A heat exchanger assembly that in a preferred embodiment comprises: an inlet duct lower wall interfacing with a bypass duct; an outlet duct lower wall interfacing with a bypass duct; a heat exchanger coupled between the inlet duct lower wall and the outlet duct lower wall wherein the heat exchanger is at a compound angle with respect to an inlet duct air flow direction; and a fairing coupled to the top of the heat exchanger wherein the fairing forms the inlet duct upper wall and the outlet duct upper wall.