A method for operating a hybrid-electric propulsion system of an aircraft, the hybrid-electric propulsion system comprising a gas turbine engine having a starter system, a high pressure system, a low pressure system, a first electric machine coupled to the low pressure system, and a second electric machine coupled to the high pressure system, the first electric machine and the second electric machine separate from the starter system, the method comprising:
- during a flight, receiving data indicative of an actual or anticipated in-flight shutdown of the gas turbine engine;
- and
- during the flight, adding power to the gas turbine engine within five seconds after receiving data of the actual in-flight shutdown through the first electric machine and the second electric machine in response to receiving data indicative of the actual or anticipated in-flight shutdown of the gas turbine engine;
- wherein adding power to the gas turbine engine comprises adding power using the first electric machine and the second electric machine to maintain a rotation speed of the low pressure system and the high pressure system of at least 25% of a pre-shutdown rotation speed of the low pressure system and the high pressure system throughout the actual in-flight shutdown and a subsequent restart of the gas turbine engine,
- wherein adding power to the gas turbine engine comprises adding at least 10 horsepower and up to 1000 horsepower,
- wherein adding power to the gas turbine engine comprises adding power to the high pressure system to reduce an exhaust gas temperature of the gas turbine engine by at least 10° Celsius and up to 100° Celsius, and
- wherein adding power to the gas turbine engine includes adding power to the low pressure system of the gas turbine engine using the first electric machine embedded within the gas turbine engine at a location aft of a turbine section of the gas turbine engine and inward of a core airflow path through the gas turbine engine to reduce a rate of deceleration of components of the gas turbine engine following the actual in-flight shutdown, decrease a first amount of time required for the gas turbine engine to get back to the pre-shutdown rotational speed following the actual in-flight shutdown, and reduce altitude loss during the subsequent restart of the gas turbine engine;
- and adding power to the high pressure system of the gas turbine engine using the second electric machine in electrical communication with an electric power bus and inward of the core airflow path through the gas turbine engine to reduce the rate of deceleration of the components of the gas turbine engine following the actual in-flight shutdown, decrease the first amount of time required for the gas turbine engine to get back to the pre- shutdown rotational speed following the actual in-flight shutdown, and reduce altitude loss during the subsequent restart of the gas turbine engine.