Hybrid electric idle and braking for an aircraft

An engine system of an aircraft, the engine system comprising:

• an energy storage system;
• a first gas turbine engine comprising a low spool, a high spool, a low-spool generator operably coupled to the low spool, and a high-spool electric motor operably coupled to the high spool;
• and
• a controller configured to:
• detect a braking condition of the aircraft;
• determine a fuel combustion state of the first gas turbine engine and a second gas turbine engine of the aircraft;
• determine an electrical demand of the aircraft from the energy storage system associated with the fuel combustion state of the first gas turbine engine and the second gas turbine engine;
• determine a storage capacity state of the energy storage system;
• transfer power from the low-spool generator to the energy storage system based on the storage capacity state of the energy storage system and the electrical demand;
• and
• transfer power to the high spool through the high-spool electric motor to support combustion in the first gas turbine engine while a rotational speed of the low spool is reduced responsive to the low-spool generator extracting energy from the low spool.