There are provided aircraft air conditioning systems and methods. The aircraft air conditioning system has a duct in an aircraft connected to an aircraft cabin and configured to flow pressurized cabin outflow air from the aircraft cabin. The aircraft air conditioning system further has a turbine connected to the duct and configured to reduce a temperature of the pressurized cabin outflow air and to generate power, and further has a compressor configured to generate a compressed inlet air stream, and further has an air conditioning pack configured to receive a reduced temperature cabin outflow air from the turbine and configured to receive the compressed inlet air stream from the compressor. The air conditioning pack has a cooling cycle system, a humidity control system, and one or more heat exchangers configured to use the reduced temperature cabin outflow air as a heat sink.