An environmental control system for an aircraft comprising: a plurality of heat exchangers (110, 130; 210, 230); a compressing device (120; 220; 320) in communication with first and second heat exchangers (110, 130; 210, 230) of the plurality of heat exchangers (110, 130; 210, 230), the compressing device (120; 220; 320) being configured to regulate a pressure of air for a cabin, which is bled from a low pressure location of an engine core and flows from the first heat exchanger (110; 210) to the second heat exchanger (130; 230) via the compressing device (120; 220; 320), from a first pressure to a second pressure that is higher than the first pressure, wherein the compressing device (120; 220; 320) comprises: a shaft; a compressor fan; and a turbine arranged to drive the compressor fan via the shaft to regulate the pressure of the air; a flow valve located upstream from the first heat exchanger (110; 210) and configured to control retrieval of a portion of the air for powering the turbine, such that the portion of air is supplied to the turbine, while the rest of the air goes through the first heat exchanger (110; 210); and an outlet to the aircraft cabin, characterised by further comprising: a cross valve located downstream of the second heat exchanger (130; 230), such that the rest of the air can proceed directly from the second heat exchanger (130; 230) through the cross valve to the outlet; and a further outlet for exiting the portion of air, utilized by the turbine, from the environmental control system. a plurality of heat exchangers (110, 130; 210, 230); a compressing device (120; 220; 320) in communication with first and second heat exchangers (110, 130; 210, 230) of the plurality of heat exchangers (110, 130; 210, 230), the compressing device (120; 220; 320) being configured to regulate a pressure of air for a cabin, which is bled from a low pressure location of an engine core and flows from the first heat exchanger (110; 210) to the second heat exchanger (130; 230) via the compressing device (120; 220; 320), from a first pressure to a second pressure that is higher than the first pressure, wherein the compressing device (120; 220; 320) comprises: a shaft; a compressor fan; and a turbine arranged to drive the compressor fan via the shaft to regulate the pressure of the air; a shaft; a compressor fan; and a turbine arranged to drive the compressor fan via the shaft to regulate the pressure of the air; a flow valve located upstream from the first heat exchanger (110; 210) and configured to control retrieval of a portion of the air for powering the turbine, such that the portion of air is supplied to the turbine, while the rest of the air goes through the first heat exchanger (110; 210); and an outlet to the aircraft cabin, characterised by further comprising: a cross valve located downstream of the second heat exchanger (130; 230), such that the rest of the air can proceed directly from the second heat exchanger (130; 230) through the cross valve to the outlet; and a further outlet for exiting the portion of air, utilized by the turbine, from the environmental control system. a cross valve located downstream of the second heat exchanger (130; 230), such that the rest of the air can proceed directly from the second heat exchanger (130; 230) through the cross valve to the outlet; and a further outlet for exiting the portion of air, utilized by the turbine, from the environmental control system.