An aircraft air conditioning system, which comprises: - an ambient air supply line adapted to be flown through with ambient air, - an ambient air cooling apparatus, which is connected to the ambient air supply line and is configured to cool the ambient air flowing through the ambient air supply line, - an ambient air discharge line, which is connected to the ambient air cooling apparatus and is connectable to an aircraft cabin, in order to conduct ambient air cooled by the ambient air cooling apparatus into the aircraft cabin, - a process air supply line, adapted to be flown through with compressed process air, - a process air cooling apparatus, which is connected to the process air supply line and is configured to cool the compressed process air flowing through the process air supply line, - a process air discharge line, which is connected to process air cooling apparatus and is connectable to the aircraft cabin, in order to conduct process air cooled by the process air cooling apparatus into the aircraft cabin, and - a refrigerating apparatus, which comprises a refrigerant circuit adapted to be flown through with a refrigerant and being thermally coupled to the ambient air cooling apparatus and the process air cooling apparatus, in order to transfer thermal energy from the ambient air cooling apparatus and the process air cooling apparatus to the refrigerant circulating in the refrigerant circuit, characterized by a bypass line branching off from the process air discharge line, which bypass line is configured to discharge cooled process air flowing through the process air discharge line into an aircraft environment, at least in certain operating phases of the aircraft air conditioning system. - an ambient air supply line adapted to be flown through with ambient air, - an ambient air cooling apparatus, which is connected to the ambient air supply line and is configured to cool the ambient air flowing through the ambient air supply line, - an ambient air discharge line, which is connected to the ambient air cooling apparatus and is connectable to an aircraft cabin, in order to conduct ambient air cooled by the ambient air cooling apparatus into the aircraft cabin, - a process air supply line, adapted to be flown through with compressed process air, - a process air cooling apparatus, which is connected to the process air supply line and is configured to cool the compressed process air flowing through the process air supply line, - a process air discharge line, which is connected to process air cooling apparatus and is connectable to the aircraft cabin, in order to conduct process air cooled by the process air cooling apparatus into the aircraft cabin, and - a refrigerating apparatus, which comprises a refrigerant circuit adapted to be flown through with a refrigerant and being thermally coupled to the ambient air cooling apparatus and the process air cooling apparatus, in order to transfer thermal energy from the ambient air cooling apparatus and the process air cooling apparatus to the refrigerant circulating in the refrigerant circuit, characterized by a bypass line branching off from the process air discharge line, which bypass line is configured to discharge cooled process air flowing through the process air discharge line into an aircraft environment, at least in certain operating phases of the aircraft air conditioning system.