Fuel system

A fuel control system for a gas turbine engine comprising,

• a main fuel metering valve for controlling the flow of fuel to a respective gas turbine engine in use, the valve including a valve control member moveable relative to a valve body by fluid pressure applied to a pressure chamber of the valve, to control the quantity of fuel supplied through the valve between zero in a valve closed condition and a maximum in a valve fully-open condition,
• a first fluid control valve operable to control the application of fluid pressure to said pressure chamber of said metering valve to determine the setting of said metering valve and thus the quantity of fuel supplied to the gas turbine engine through the metering valve,
• means for detecting an over-speed operating condition of the respective gas turbine engine in use, and,
• a second fluid control valve moveable from a first condition to a second condition in response to detection of such over-speed condition, said second fluid control valve serving in said first condition to apply fluid pressure derived from said first fluid control valve to said pressure chamber of said metering valve, and serving in its said second condition to prevent the application of fluid pressure derived from said first fluid control valve to said pressure chamber of said metering valve and to vent said pressure chamber to permit said control member of said metering valve to move towards a valve closed position.