Abstract: A high turndown mass flow control system for the regulation of gas flow to a variable pressure system such as a gas turbine engine. The herein described system controls the flow of gas into a load system where the gas delivery pressure at the load varies directly as a function of the mass flow. The system employs flow control and mass flow measurement subsystems, controlling the mass flow to maintain a mass reference value called for by an outside master control. Flow control apparatus includes a throttling control valve while the flow measurement subsystem includes a flow restriction element, .delta.P, pressure and temperature transducers while using a flow calculation algorithm to calculate the actual gas mass flow passing through the system. The high turndown mass flow control characteristic of the invention acquired by an unique placement and usage of the gas restriction element allows the reading of .delta.P parameters with conventional instrumentation.