An airplane is provided. The airplane includes a pressurized volume and an air conditioning system. The air conditioning system includes a compressor configured to receive a flow of a first medium, a turbine downstream of the compressor in a flow path of the first medium, a first valve that diverts the flow of the first medium around the turbine, a second valve that provides a second medium to the turbine, and a third valve downstream of the turbine that directs an outlet flow of the turbine towards the pressurized volume and that directs the outlet flow of the turbine away from the pressurized volume.