Abstract: A gas turbine engine is supplied with fuel by way of a metering unit which includes a metering valve responsive to a servo pressure which is regulated by electrical signals from a control circuit. Failure of electrical signals to the metering unit results in the metering valve being arrested in its position at failure. A combined manually operable and shut-off valve arrangement is in series with the metering unit includes a valve which is normally biassed fully open and is operable by a manually regulated servo pressure. The manually operable arrangement also includes a device for setting the servo pressure of the valve in the metering unit to a value which maintains that metering valve fully open.

Abstract: The main metering valve of a gas turbine fuel control system is positioned by a servo pressure signal controlled by a servo valve. The servo valve is positioned by the sum of forces derived from the operating positions of a torque motor and a stepping motor. If both motors are de-energized by electrical failure the servo valve, and hence the main metering valve is maintained in a position which corresponds to the steady-running fuel flow at the time of failure.