A method of operating a fuel delivery system of an aircraft engine of an aircraft includes operating the aircraft engine in a standby mode by maintaining combustion in a combustor of the aircraft engine by supplying fuel to the combustor via a first set of fuel nozzles of a first fuel manifold while providing a trickle flow of fuel via a second set of fuel nozzles of a second fuel manifold into the combustor during engine operation, the trickle flow being defined as a fuel flow rate selected to prevent flame-out of the combustion while providing one of: substantially no motive power to the aircraft, and no motive power to the aircraft, via the combustion of the trickle flow of fuel. An aircraft gas turbine engine is also described.

An aircraft that includes a hybrid-electric propulsion system is provided. In one aspect, the hybrid-electric propulsion system includes at least one propulsor that includes a gas turbine engine and an electric machine mechanically coupled with a spool of the gas turbine engine. When idle operation is commanded, electrical power is provided to the electric machine to cause the electric machine to apply torque to the spool and fuel provided to the engine can be reduced. Thus, the electric machine is controlled to provide a power assist to maintain the engine at the commanded idle speed whilst reducing fuel consumption.

An aircraft engine, has: a low-pressure compressor and a high-pressure compressor located downstream of the low-pressure compressor; a gaspath valve upstream of the high-pressure compressor, the gaspath valve movable between an open configuration and a closed configuration; and a bypass flow path having in flow series a bypass inlet, a bypass valve, and a bypass outlet, the bypass inlet fluidly communicating with the gaspath upstream of at least one stage of the low-pressure compressor, the bypass valve having an open configuration in which the bypass valve allows a bypass flow and a closed configuration in which the bypass valve blocks the bypass flow, the bypass outlet fluidly communicating with the bypass inlet via the bypass valve and with the gaspath at a location in the gaspath fluidly downstream of the gaspath valve, downstream of the low-pressure compressor, and upstream of the high-pressure compressor.

A method is provided for operating an aircraft system. During this method, an engine is operated using first fuel provided by a first fuel source. A fuel supply for the engine is switched between the first fuel source and a second fuel source, where the switching of the fuel supply includes shutting down the engine during aircraft flight. The engine is operated using second fuel provided by the second fuel source.

Methods and systems for supply of fuel for a turbine-driven fracturing pump system used in hydraulic fracturing may be configured to identify when the supply pressure of primary fuel to a plurality of gas turbine engines of a plurality of hydraulic fracturing units falls below a set point, identify a gas turbine engine of the fleet of hydraulic fracturing units operating on primary fuel with highest amount of secondary fuel available, and to selectively transfer the gas turbine engine operating on primary fuel with the highest amount of secondary fuel from primary fuel operation to secondary fuel operation. Some methods and systems may be configured to transfer all gas turbine engines to secondary fuel operation and individually and/or sequentially restore operation to primary fuel operation and/or to manage primary fuel operation and/or secondary fuel operation for portions of the plurality of gas turbine engines.

Various implementations described herein are directed to an aircraft having a multi-engine configuration with multiple engines. The aircraft may have a flight control system coupled to the multiple engines with a multi-engine interface. The flight control system may be configured to shutdown at least one engine of the multiple engines during reduced-engine operation by continuously calculating altitude for the reduced-engine operation based on one or more of an aircraft descent rate of the aircraft and an engine restart time of the at least one engine.

Various implementations described herein are directed to an aircraft having a multi-engine configuration with multiple engines. The aircraft may have a flight control system coupled to the multiple engines with a multi-engine interface. The flight control system may be configured to shutdown at least one engine of the multiple engines during reduced-engine operation by continuously calculating altitude for the reduced-engine operation based on one or more of an aircraft descent rate of the aircraft and an engine restart time of the at least one engine.

A system of a hybrid aircraft includes a first gas turbine engine including a fan, a high speed spool, and a low spool motor configured to drive rotation of the fan. The system also includes a second gas turbine engine and a controller. The controller is operable to determine an operating mode of the hybrid aircraft, control the low spool motor to drive rotation of the fan of the first gas turbine engine responsive to a thrust command while the second gas turbine engine is driven by commanding fuel combustion based on the operating mode, and accelerate the high speed spool of the first gas turbine engine and command fuel combustion at the first gas turbine engine based on a transition of the operating mode to perform a starting operation of the first gas turbine engine.

The turboshaft engine for a rotorcraft includes a low pressure spool having a low pressure compressor and a low pressure turbine section, and a high pressure spool having a high pressure compressor and a high pressure turbine section. The spools are independently rotatable relative to one another. The low pressure compressor section includes a mixed flow rotor. A set of variable guide vanes (VGVs) are discposed upstream of each of the low pressure and high pressure compressors, the VGVs being configured to be independently operable relative to one another.

Methods and systems of operating a gas turbine engine in a low-power condition are provided. In one embodiment, the method includes supplying fuel to a combustor by supplying fuel to a first fuel manifold and a second fuel manifold of the gas turbine engine. The method also includes, while supplying fuel to the combustor by supplying fuel to the first fuel manifold: stopping supplying fuel to the second fuel manifold; and supplying pressurized air to the second fuel manifold to flush fuel in the second fuel manifold into the combustor and hinder coking in the second fuel manifold and associated fuel nozzles.