A method of operating a gas turbine engine having a turbine and a compressor connected via a shaft, a main fuel supply line for supplying fuel to a combustor that is positioned to release expanding hot gases to the turbine, the engine further including a starter/generator connected to the shaft via a gearbox assembly, the method is characterised the step of during engine start up fuel is circulated in a re-circulating fuel circuit positioned on the main fuel supply line and which has a first fuel/oil heat exchanger, for cooling the oil, and a fuel accumulator.