An environmental control system, ECS, for an aircraft comprising: at least one cooling turbine (30, 62); a compressor; a primary heat exchanger and a secondary heat exchanger; and a turbine bypass valve disposed fluidly upstream of a first air load, the turbine bypass valve configured to: direct a first portion of an ECS output airflow to the first air load at a first pressure via a first outlet passage; and direct a second portion of the ECS output airflow across a cooling turbine of the at least one cooling turbine via a turbine inlet passage and to a second air load at a second pressure lower than the first pressure for cooling thereof; wherein the at least one cooling turbine includes a first cooling turbine and a second cooling turbine of the ECS, with the turbine bypass valve configured to: direct the first portion of an ECS output airflow from the first cooling turbine to the first air load and bypass the second cooling turbine; and direct the second portion of the ECS output airflow from the first cooling turbine across the second cooling turbine and to the second air load; wherein the compressor is arranged on a common shaft with the first cooling turbine; and wherein the compressor is fluidly coupled to an outlet of the primary heat exchanger and an inlet of the secondary heat exchanger of the ECS; wherein the turbine bypass valve is disposed at a fluid pathway between the first cooling turbine and the second cooling turbine of the ECS; the environmental control system further comprising a condensing heat exchanger disposed on the fluid pathway between the first cooling turbine and the second cooling turbine; and wherein the turbine bypass valve is disposed fluidly downstream of the condensing heat exchanger, between the condensing heat exchanger and the first air load. at least one cooling turbine (30, 62); a compressor; a primary heat exchanger and a secondary heat exchanger; and a turbine bypass valve disposed fluidly upstream of a first air load, the turbine bypass valve configured to: direct a first portion of an ECS output airflow to the first air load at a first pressure via a first outlet passage; and direct a second portion of the ECS output airflow across a cooling turbine of the at least one cooling turbine via a turbine inlet passage and to a second air load at a second pressure lower than the first pressure for cooling thereof; direct a first portion of an ECS output airflow to the first air load at a first pressure via a first outlet passage; and direct a second portion of the ECS output airflow across a cooling turbine of the at least one cooling turbine via a turbine inlet passage and to a second air load at a second pressure lower than the first pressure for cooling thereof; wherein the at least one cooling turbine includes a first cooling turbine and a second cooling turbine of the ECS, with the turbine bypass valve configured to: direct the first portion of an ECS output airflow from the first cooling turbine to the first air load and bypass the second cooling turbine; and direct the second portion of the ECS output airflow from the first cooling turbine across the second cooling turbine and to the second air load; direct the first portion of an ECS output airflow from the first cooling turbine to the first air load and bypass the second cooling turbine; and direct the second portion of the ECS output airflow from the first cooling turbine across the second cooling turbine and to the second air load; wherein the compressor is arranged on a common shaft with the first cooling turbine; and wherein the compressor is fluidly coupled to an outlet of the primary heat exchanger and an inlet of the secondary heat exchanger of the ECS; wherein the turbine bypass valve is disposed at a fluid pathway between the first cooling turbine and the second cooling turbine of the ECS; the environmental control system further comprising a condensing heat exchanger disposed on the fluid pathway between the first cooling turbine and the second cooling turbine; and wherein the turbine bypass valve is disposed fluidly downstream of the condensing heat exchanger, between the condensing heat exchanger and the first air load.