Metering demand fuel system for gas turbine engines

A fuel system (10) includes a turbine engine (12), and an electric motor (30) that are independently drivable relative to one another. The electric motor (30) has a speed that is selectively controlled based upon a desired fuel flow. A centrifugal pump (24) is driven by the turbine engine (12). The centrifugal pump (24) provides a desired fuel pressure for the fuel system. A positive displacement pump (26) is driven by the electric motor (30). The positive displacement pump (26) is in fluid communication with the centrifugal pump (24), for example in a series arrangement. The positive displacement pump (26) meters a desired volume in response to the speed of the motor (30).