 Raisbeck went on in 1983 to develop Quiet Turbofan Propellers for the King Air with Hartzell Propeller.The same propeller technology was later used by Raisbeck and Hartzell to develop a Quiet Turbofan Propeller for the de Havilland Canada DHC-6 Twin Otter.Installed on the King Air, the quiet propellers reduce the perceived noise levels enough to allow the airplanes to operate out of European airports with the most stringent noise requirements.