MASS FLOW METERING METHOD AND SYSTEM

A fuel supply system for a gas turbine engine includes a low flow circuit that branches off parallel to a main flow circuit from an upstream main flow line (39) upstream of a metering valve (34) and has an upstream low flow line (38) having a line connected to an orifice (40) having an upstream side and a downstream side. The downstream side of the orifice is connected to a mass flow meter (42). A return low flow line (32) is downstream of the mass flow meter and connected into the downstream main flow line at a downstream point. A controller (46) is programmed to take in a low flow circuit mass flow measured by the mass flow meter, and calculate a main mass flow through the main flow circuit and the total mass flow delivered to the engine. A gas turbine engine and a method of operation are also disclosed.