Abstract: A method and apparatus for conditioning a supply of bleed air from an aircraft engine to a system using such bleed air, including passing the bleed air to a turbine over which the air is expanded to produce a power output, and regulating the power output thereby to control the condition of the air downstream of the turbine.

Abstract: An air cycle cooling system for cooling a first heat load and a second heat load, the system including a compressor to pressurise air in the system, and an expansion apparatus for allowing the compressed air to expand and cool for use in cooling the first and second heat loads, and wherein at least a proportion of the air utilised for cooling the first heat load is recycled to the compressor and at least a proportion of the air utilised for cooling the second heat load is utilised as a coolant in a primary heat exchanger to cool the air from the first heat load prior to the air from the first heat load being expanded in the expansion apparatus.