<div class="htmlview paragraph">In further studies of Advanced Supersonic Transport (AST) powerplants the relative merits of several different engine cycles have been compared. The influence of the noise levels which have to be met is shown to be a dominant factor on the design of both the powerplant and the aircraft. An uprated turbofan derivative of the pure jet Olympus 593 Concorde engine could provide a satisfactory powerplant for a quiet and economically viable AST having improved pollution characteristics.</div>