Fuel delivery

A method of operating a gas turbine engine for an aircraft, the gas turbine engine comprising a staged combustion system having pilot fuel injectors and main fuel injectors, the staged combustion system being operable in a pilot-only range of operation and a pilot-and-main range of operation, the method comprising:

• determining one or more fuel characteristics of a fuel being supplied to the staged combustion system;
• determining a staging point, defining the point at which the staged combustion system is switched between pilot-only operation and pilot-and-main operation, based on the determined one or more fuel characteristics;
• and
• controlling the staged combustion system according to the determined staging point, wherein
• the one or more fuel characteristics indicate that the fuel is associated with a lower nvPM production level compared to fossil kerosene, and the one or more fuel characteristics, based on which the staging point is determined, are determined using sensor data from a sensor,
• the determined staging point is a cruise staging point,
• the combustion system is controlled using the determined staging point during a cruise operating condition of the engine, and
• the staging point is determined such that the staged combustion system is arranged to switch between the pilot-only range of operation and the pilot-and-main range of operation at a staging point which corresponds to a steady state cruise mode of operation of the engine, the staging point defining a boundary between a first cruise operation range and a second cruise operation range.