A aircraft gas turbine engine and operation method, the engine including: a staged combustion system having pilot and main fuel injectors, and operates in a pilot-only range wherein fuel delivers to pilot fuel injectors, and a pilot-and-main operation range wherein fuel is delivered to at least the main fuel injectors. The engine further includes a fuel delivery regulator to pilot and main fuel injectors, which receives fuel from a first and second source containing fuels each with different characteristics. The staged combustion system switches between pilot-only and pilot-and-main range operation when in steady cruise mode, the mode defining a boundary between first and second engine cruise operation range. The fuel delivery regulator delivers fuel to pilot fuel injectors during at least part of the first engine cruise operation with different fuel characteristics from fuel delivered to one or both pilot and main fuel injectors the second engine cruise operation range.

A method is provided which includes: processing first fuel data to determine a first trend of a powerplant performance characteristic for a first fuel, wherein the first fuel data is indicative of a plurality of first values of a tracked operational parameter for an aircraft powerplant model over a period of time, and the first values were recorded when combusting the first fuel; processing second fuel data to determine a second trend of the powerplant performance characteristic for a second fuel, wherein the second fuel data is indicative of a plurality of second values of the tracked operational parameter for the aircraft powerplant model over the period of time, and the second values were recorded when combusting the second fuel; and scheduling use of the first fuel and the second fuel based on the first trend of the powerplant performance characteristic and the second trend of the powerplant performance characteristic.

A method of operating a dual fuel gas turbine engine includes operating the engine with a first fuel according to a first control loop. The method also includes while the engine is operating with the first fuel, bumplessly transitioning the engine to operate with a second fuel, and operating the engine with the second fuel according to a second control loop.