An open-rotor gas turbine engine comprising a starter/generator, a first spool and a second spool, the second spool is of a lower pressure than the first spool; wherein the starter/generator is connected to the first and second spools via first and second clutches respectively. The method of operating the open-rotor engine comprises the step of supplying power to the starter/generator to drive the first spool via the first clutch to start the engine and, once the engine is self-propelling, a step of driving the starter/generator from the second spool via the second clutch to generate electricity.