An aviation bypass valve for use in a heat exchanger apparatus, including a shape memory alloy material. The heat exchanger apparatus further including an air-cooled oil cooler disposed in a bypass fan duct of an aircraft engine. The heat exchanger apparatus including a bypass valve in fluid communication with the air cooled oil cooler. The bypass valve including a valve body, a piston disposed in the valve body and moveable therein and an actuation component. The actuation component including a shape memory alloy. The actuation component responsive to a change in at least one of a thermal condition and a pressure exerted thereon so as to move the piston, thereby opening and closing the bypass valve.