Hydrogen fuelled gas turbine engine

A fuel system for a gas turbine engine configured to combust hydrogen fuel, the fuel system comprising:

• a main fuel conduit;
• a fuel pump configured to operate on liquid hydrogen within the fuel conduit to provide pressurised fuel to a combustor of the gas turbine engine;
• a fuel metering unit configured to control fuel flow delivered to the combustor;
• a controller configured to control the fuel pump and the fuel metering unit wherein
• the fuel pump is configured to provide hydrogen at an outlet above a critical temperature and pressure, to thereby provide supercritical hydrogen fuel downstream;
• the fuel metering unit is configured to provide a variable flow area downstream of the pump, to deliver fuel at required flow parameters;
• the controller is configured to control the fuel metering unit in accordance with a schedule in accordance with a fuel mass-flow demand setpoint;
• and
• the schedule comprises inputs comprising the fuel mass-flow demand setpoint, static pressure upstream and downstream of the fuel metering unit, and temperature upstream of the fuel metering unit, and an output comprising a valve position setpoint.