Cooling capacity of the F-15 environmental control system (ECS) has been significantly increased in the current F-15 growth system by applying the high-pressure water separation (HPWS) technique. To further increase the F-15 ECS thermal cycle efficiency, an advanced high-temperature, turbine-powered bootstrap air cycle system has been designed to operate directly from the engine bleed air source. The advanced system more fully exploits the engine compressor bleed air energy potential by using the bleed air at maximum pressure and temperature to drive a power turbine. The power turbine pre cools the bleed air and drives a closed-loop bootstrap air cycle cooling system.The advanced system significantly reduces aircraft fuel consumption because it requires less bleed air and ram air. Furthermore, because it has fewer parts, the projected system reliability is increased and weight is reduced.The paper introduces the subject through a brief discussion of the recent air cycle system approaches and engine bleed air preconditioning techniques. Thermal cycle diagrams compare the advanced high-temperature, turbine-powered bootstrap with the F-15 growth system at extreme operating conditions.