Acceleration of a gas turbine

A method of operating a gas turbine engine in an aircraft, the gas turbine engine having a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine;

• a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine;
• a combustion system comprising a fuel metering unit;
• an energy storage system;
• and an engine controller, the method comprising:
• determining that a throttle lever angle setting has changed, the throttle lever angle setting indicative of an acceleration event;
• increasing fuel flow to the combustion system by the fuel metering unit;
• determining that a state of charge of the energy storage system is greater than a minimum value;
• determining that a total aircraft power demand is less than a maximum power available from the energy storage system;
• and
• responsive to determining that the state of charge of the energy storage system is greater than the minimum value and determining that the total aircraft power demand is less than the maximum power available from the energy storage system, supplying the total aircraft power demand using the energy storage system, supplying excess power from the energy storage system to the first electric machine and operating the first electric machine in a motor mode to increase the HP spool rotational speed and engine core mass flow.