Propulsion system control

A method of operating an aircraft comprising a gas turbine engine and a plurality of fuel tanks configured to store fuel to power the gas turbine engine, the method comprising:

• arranging two fuel tanks of the plurality of fuel tanks to each store a different fuel;
• starting the gas turbine engine;
• providing only fuel from a second fuel tank of the two fuel tanks to the gas turbine engine while starting the gas turbine engine;
• switching fuel supply from the second fuel tank to a first fuel tank of the two fuel tanks after starting the gas turbine engine;
• performing operations on the ground after starting the gas turbine engine and prior to take-off;
• providing fuel only from the first fuel tank to the gas turbine engine while performing the operations on the ground after starting the gas turbine engine and prior to take-off;
• performing in-flight operations;
• and
• providing fuel from only the second fuel tank during a majority of the in-flight operations.

A power system for an aircraft comprising:

• a gas turbine engine configured to burn a fuel in a combustor so as to provide power to the aircraft;
• a plurality of fuel tanks, each configured to contain a fuel to be used to provide power to the aircraft, the plurality of fuel tanks including a first fuel tank and a second fuel tank that are configured to contain different fuels;
• and
• a controller configured to store information on fuel contained in each fuel tank and to control fuel supply to the gas turbine engine so as to:
• take fuel from only the second fuel tank for engine start-up, before switching to the first fuel tank,
• supply fuel from only the first fuel tank to the gas turbine engine when performing operations on the ground after the engine start-up and prior to take-off, and
• supply fuel from only the second fuel tank during a majority of in-flight operations.

A power system for an aircraft comprising:

• a gas turbine engine configured to burn a fuel in a combustor so as to provide power to the aircraft;
• a plurality of fuel tanks, each configured to contain a fuel to be used to provide power to the aircraft, the plurality of fuel tanks including a first fuel tank and a second fuel tank that are configured to contain different fuels, wherein the first fuel tank is a trim tank of the aircraft, and the first fuel tank contains sustainable aviation fuel, and
• a controller configured to store information on fuel contained in each fuel tank and to control fuel supply to the gas turbine engine so as to:
• take fuel from the second fuel tank for engine start-up, before switching to the first fuel tank, and
• supply the sustainable aviation fuel from the first fuel tank to the gas turbine engine when performing operations on the ground after the engine start-up and prior to take-off so that the sustainable aviation fuel in the first fuel tank is used up performing the operations on the ground and the first fuel tank is at least substantially empty and available to receive fuel pumped thereinto in flight.