Air conditioning system for an aircraft cabin

An air-conditioning system for airplanes is proposed in which a portion of the fresh airflow to be prepared is tapped at high pressure from a power unit and another portion is sucked in from the surroundings. The energy potential of the tapped airflow is utilized to compress the ambient air. The compressed ambient air and the tapped air are mixed into a mixed airflow before the mixed airflow's pressure is expanded in one or more turbine stages (T1, T2). Water is separated from the mixed airflow between the mixing point (X) and the first turbine stage 1 (T1). In order to cool down the tapped airflow to a temperature at which water can be separated at all, the tapped airflow is guided past the entire cooler mixed airflow, preferably in two steps (REH, CON), namely once before the pressure expansion and another time after the pressure expansion of the mixed airflow in the first turbine stage (T1) . In a preferred form of execution, the ambient air is compressed in two steps, in connection with which in each case a compressor wheel (C1, C2) and a turbine wheel (T2, T1) (two-step pressure expansion) are mounted together on a shaft.