An environmental control system for an aircraft uses engine bleed air for cabin environment control. The environment control system regulates the inlet airflow by assessing a plurality of parameters that provides, but not limited to, the aircraft operating conditions and external environment data, aiming at substantially reducing the extracted engine bleed air demand for cabin environment control and fuel consumption reduction and concurrently complying with aircraft pressurization, ventilation and thermal load requirements. The environmental control system airflow target is calculated based on the actual aircraft operating conditions, external environment data and a multi-dimensional airflow schedule map. Then, environmental control system airflow target is further trimmed based on the actual aircraft operating conditions and air conditioning system performance capabilities by fixing the air conditioning airflow outlet temperature and then regulating the air conditioning inlet mass airflow through the flow control valve. The first control method reduces and the second one trims the environmental control system airflow target comparing to conventional control methods. Thus, fuel consumption reduction is obtained when the environment control system airflow target (extracted bleed air demand) can be reduced and or trimmed depending on flight conditions.