A computer-implemented method of assessing a health of a gas turbine engine of a hybrid-electric propulsion system for an aircraft, the hybrid-electric propulsion system comprising an electric machine rotatable with the gas turbine engine, the method comprising: changing, by one or more computing devices, an amount of fuel (R 0, R 1) provided to the combustion section of the gas turbine engine for an amount of time (t 0, t 1); receiving, by one or more computing devices, data indicative of an amount of electrical power provided to, or extracted from, the electric machine; determining, by the one or more computing devices, a change in the amount of electrical power provided to, or extracted from, the electric machine during at least a portion of the time that the amount of fuel is changed receiving, by the one or more computing devices, data indicative of an operating parameter of the hybrid-electric propulsion system; assessing, by the one or more computing devices, a health of the gas turbine engine based at least in part on the received data indicative of the amount of electrical power provided to, or extracted from, the electric machine and the received data indicative of the operating parameter of the hybrid electric propulsion system; assessing by the one or more computing devices, the health of the gas turbine engine based at least in part on the received data indicative of the change in the amount of fuel provided to the combustion section of the gas turbine engine and the received data indicative of the change in the amount of electrical power provided to, or extracted from, the electric machine during at least a portion of the amount of time; and providing, by the one or more computing devices, information to a user indicative of the health of the gas turbine engine. changing, by one or more computing devices, an amount of fuel (R 0, R 1) provided to the combustion section of the gas turbine engine for an amount of time (t 0, t 1); receiving, by one or more computing devices, data indicative of an amount of electrical power provided to, or extracted from, the electric machine; determining, by the one or more computing devices, a change in the amount of electrical power provided to, or extracted from, the electric machine during at least a portion of the time that the amount of fuel is changed receiving, by the one or more computing devices, data indicative of an operating parameter of the hybrid-electric propulsion system; assessing, by the one or more computing devices, a health of the gas turbine engine based at least in part on the received data indicative of the amount of electrical power provided to, or extracted from, the electric machine and the received data indicative of the operating parameter of the hybrid electric propulsion system; assessing by the one or more computing devices, the health of the gas turbine engine based at least in part on the received data indicative of the change in the amount of fuel provided to the combustion section of the gas turbine engine and the received data indicative of the change in the amount of electrical power provided to, or extracted from, the electric machine during at least a portion of the amount of time; and providing, by the one or more computing devices, information to a user indicative of the health of the gas turbine engine.