Patent Description:
Gas turbine engines of an aircraft can have different starting requirements for ground-based starting and in-flight restarting. Ground-based starting is performed at a steady altitude, while in-flight restarting can occur during a change in altitude and speed of the aircraft. In-flight starting can use a windmill effect to drive engine spool rotation by decreasing aircraft altitude. A windmill envelope defines a range of altitudes and airspeeds where windmill restarting can be effectively performed that minimizes that chances of rotor lock, dual flameout, or other issues.

<CIT> discloses a mechanism for turbine engine start using the low speed spool. <CIT> discloses an apparatus for windmill starts in gas turbine engines. <CIT> discloses a system for low spool power extraction. <CIT> discloses a system with an electromagnetic clutch between two spools.

According to one embodiment, a system includes a gas turbine engine having a low speed spool and a high speed spool. The system also includes a spool coupling system comprising an electro-mechanical actuator and a clutch configured to mechanically link the low speed spool and the high speed spool. A controller is operable to determine a mode of operation of the gas turbine engine, monitor for a spool coupling activation condition associated with the mode of operation, and activate the electro-mechanical actuator of the spool coupling system based on the controller detecting the spool coupling activation condition. Engagement of the clutch and power transfer between the low speed spool and the high speed spool occurs based on activation of the electro-mechanical actuator of the spool coupling system and reaching an engagement condition of the clutch of the spool coupling system. The controller is further operable to deactivate the electro-mechanical actuator of the spool coupling system after disengagement of the clutch to prevent reengagement of the spool coupling system above the spool coupling activation condition, where disengagement of the clutch of the spool coupling system occurs based on the gas turbine engine reaching a disengagement condition.

The system may include where the mode of operation of the gas turbine engine distinguishing between ground-based operation and flight operation.

The system may include where the spool coupling activation condition includes detecting a reduction in speed of the low speed spool below an idle condition prior to a windmill condition while the mode of operation is an in-flight mode.

The system may include where the engagement condition of the spool coupling system includes a gear ratio level of the spool coupling system aligning with a ratio of high speed spool speed to low speed spool speed.

The system may include where a stabilization condition is reached after engagement of the spool coupling system resulting in fan windmill power being transferred to the high speed spool.

The system may include where the low speed spool provides power to the high speed spool until the spool coupling system reaches a disengagement condition, and the spool coupling system is deactivated to prevent reengagement of the spool coupling system above the spool coupling activation condition.

The system may include where the mode of operation of the gas turbine engine is a sub-idle mode that activates, engages, disengages, and deactivates the spool coupling system below an idle level of operation of the gas turbine engine during flight.

The system may include where the mode of operation of the gas turbine engine is a low spool power-assisted idle that results in the high speed spool at idle when the spool coupling system is engaged.

The system may include where the spool coupling system includes a variable transmission system with multiple gear ratios and multiple levels of spool power transfer and engagement speeds.

According to an embodiment, a method includes determining, by a controller, a mode of operation of a gas turbine engine, the gas turbine engine having a low speed spool and a high speed spool. The controller monitors for a spool coupling activation condition associated with the mode of operation. An electro-mechanical actuator of the spool coupling system is activated based on the controller detecting the spool coupling activation condition. The engagement of a clutch of the spool coupling system and power transfer between the low speed spool and the high speed spool occurs based on activation of the electro-mechanical actuator of the spool coupling system and reaching an engagement condition of the clutch of the spool coupling system. The spool coupling system is configured to mechanically link the low speed spool and the high speed spool when the clutch is engaged. The method further comprises deactivating the electro-mechanical actuator of the spool coupling system after disengagement of the clutch to prevent reengagement of the spool coupling system above the spool coupling activation condition, wherein disengagement of the clutch of the spool coupling system occurs based on the gas turbine engine reaching a disengagement condition of the clutch.

A technical effect of the apparatus, systems and methods is achieved by performing gas turbine engine spool coupling.

It will be appreciated that each of the positions of the fan section <NUM>, compressor section <NUM>, combustor section <NUM>, turbine section <NUM> may be varied.

In a further example, the engine <NUM> bypass ratio is greater than about six (<NUM>), with an example embodiment being greater than about ten (<NUM>). Some embodiments can include a gear system <NUM> with an epicyclic gear train, such as a planetary gear system or other gear system, for example, with a gear reduction ratio of greater than about <NUM>. The low pressure turbine <NUM> can have a pressure ratio that is greater than about five. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans.

The fan section <NUM> of the engine <NUM> is designed for a particular flight condition--typically cruise at about <NUM> Mach and about <NUM>,<NUM> feet (<NUM>,<NUM> meters).

The gas turbine engine <NUM> includes a spool coupling system <NUM> that is configured to mechanically link the low speed spool <NUM> and the high speed spool <NUM>. The spool coupling system <NUM> can include a gear train <NUM> and clutch <NUM> that enable selective engagement and power transfer between the low speed spool <NUM> and the high speed spool <NUM>. The gear train <NUM> can include a series of gears at a gear ratio, for instance, that is activated below an idle speed of the gas turbine engine <NUM> that establishes a matching condition between the low speed spool <NUM> and the high speed spool <NUM>. In some embodiments, the spool coupling system <NUM> can be a variable speed transmission that supports a wider range of speeds. The clutch <NUM> can be a unidirectional clutch, such as a sprag. A first shaft <NUM> can link the spool coupling system <NUM> with the inner shaft <NUM>, and a second shaft <NUM> can link the spool coupling system <NUM> with the outer shaft <NUM>. Although depicted schematically in <FIG>, it will be understood that linkages and coupling can include intermediate features such as gearboxes that enable power transfer between the inner shaft <NUM>, first shaft <NUM>, gear train <NUM>, clutch <NUM>, second shaft <NUM>, and the outer shaft <NUM>. Further, the alignment of the spool coupling system <NUM> relative to components of the gas turbine engine <NUM> is depicted schematically for purposes of explanation and is not limiting with respect to sizing, placement, and other such aspects.

While the example of <FIG> illustrates one example of the gas turbine engine <NUM>, it will be understood that any number of spools, inclusion or omission of the gear system <NUM>, and/or other elements and subsystems are contemplated. Further, rotor systems described herein can be used in a variety of applications and need not be limited to gas turbine engines for aircraft applications. For example, rotor systems can be included in power generation systems, which may be ground-based as a fixed position or mobile system, and other such applications.

<FIG> illustrates a hybrid electric propulsion system <NUM> (also referred to as hybrid gas turbine engine <NUM> or hybrid propulsion system <NUM>) including a gas turbine engine <NUM> operably coupled to an electrical power system <NUM> as part of a hybrid electric aircraft. One or more mechanical power transmissions <NUM> (e.g., 150A, 150B) can be operably coupled between the gas turbine engine <NUM> and the electrical power system <NUM>. The gas turbine engine <NUM> can be an embodiment of the gas turbine engine <NUM> of <FIG> and includes one or more spools, such as low speed spool <NUM> and high speed spool <NUM>, each with at least one compressor section and at least one turbine section operably coupled to a shaft (e.g., low pressure compressor <NUM> and low pressure turbine <NUM> coupled to inner shaft <NUM> and high pressure compressor <NUM> and high pressure turbine <NUM> coupled to outer shaft <NUM> as depicted in <FIG>). The electrical power system <NUM> can include a first electric motor 212A configured to augment rotational power of the low speed spool <NUM> and a second electric motor 212B configured to augment rotational power of the high speed spool <NUM>. Although two electric motors 212A, 212B are depicted in <FIG>, it will be understood that there may be only a single electric motor (e.g., only electric motor 212B) or additional electric motors (not depicted). Further, the electric motors 212A, 212B are generally referred to as motors 212A, 212B, as alternate power sources may be used, such as hydraulic motors, pneumatic motors, and other such types of motors known in the art. The electrical power system <NUM> can also include a first electric generator 213A configured to convert rotational power of the low speed spool <NUM> to electric power and a second electric generator 213B configured to convert rotational power of the high speed spool <NUM> to electric power. Although two electric generators 213A, 213B (generally referred to as generators 213A, 213B) are depicted in <FIG>, it will be understood that there may be only a single electric generator (e.g., only electric generator 213A) or additional electric generators (not depicted). In some embodiments, one or more of the electric motors 212A, 212B can be configured as a motor or a generator depending upon an operational mode or system configuration, and thus one or more of the electric generators 213A, 213B may be omitted.

In the example of <FIG>, the mechanical power transmission 150A includes a gearbox operably coupled between the inner shaft <NUM> and a combination of the first electric motor 212A and first electric generator 213A. The mechanical power transmission 150B can include a gearbox operably coupled between the outer shaft <NUM> and a combination of the second electric motor 212B and second electric generator 213B. In embodiments where the electric motors 212A, 212B are configurable between a motor and generator mode of operation, the mechanical power transmission 150A, 150B can include a clutch or other interfacing element(s). In some embodiments, the mechanical power transmission 150A, first electric motor 212A, first electric generator 213A, and associated electronics can be omitted.

The electrical power system <NUM> can also include motor drive electronics 214A, 214B operable to condition current to the electric motors 212A, 212B (e.g., DC-to-AC converters). The electrical power system <NUM> can also include rectifier electronics 215A, 215B operable to condition current from the electric generators 213A, 213B (e.g., AC-to-DC converters). The motor drive electronics 214A, 214B and rectifier electronics 215A, 215B can interface with an energy storage management system <NUM> that further interfaces with an energy storage system <NUM>. The energy storage management system <NUM> can be a bi-directional DC-DC converter that regulates voltages between energy storage system <NUM> and electronics 214A, 214B, 215A, 215B. The energy storage system <NUM> can include one or more energy storage devices, such as a battery, a super capacitor, an ultra capacitor, and the like. The energy storage management system <NUM> can facilitate various power transfers within the hybrid electric propulsion system <NUM>. The energy storage management system <NUM> may also transfer power to one or more electric motors on the engine, or to external loads <NUM> and receive power from one or more external power sources <NUM> (e.g., aircraft power, auxiliary power unit power, cross-engine power, and the like).

A power conditioning unit <NUM> and/or other components can be powered by the energy storage system <NUM>. The power conditioning unit <NUM> can distribute electric power to support actuation and other functions of the gas turbine engine <NUM>. For example, the power conditioning unit <NUM> can power an integrated fuel control unit <NUM> to control fuel flow to the gas turbine engine <NUM>. The power conditioning unit <NUM> can also power a plurality of actuators (not depicted), such as bleed actuators, vane actuators, and the like.

The spool coupling system <NUM>, as previously described with respect to <FIG>, can be used to mechanically transfer power between the low speed spool <NUM> and the high speed spool <NUM> of the gas turbine engine <NUM>. The spool coupling system <NUM> can be activated and deactivated to operate under selected conditions, such as in support of windmill starting to directly transfer power between the low speed spool <NUM> and the high speed spool <NUM>. Further, the spool coupling system <NUM> can be activated for transferring power of an electric motor to both spools, such as using the first electric motor 212A for taxiing operations through the low speed spool <NUM> while also driving the high speed spool <NUM> to operate accessories and prepare for ground-based starting. Collectively, any effectors that can change a state of the gas turbine engine <NUM> and/or the electrical power system <NUM> may be referred to as hybrid electric system control effectors <NUM>. Examples of the hybrid electric system control effectors <NUM> can include the electric motors 212A, 212B, electric generators 213A, 213B, integrated fuel control unit <NUM>, spool coupling system <NUM>, and/or other elements (not depicted).

<FIG> is a schematic diagram of control signal paths <NUM> of the hybrid electric propulsion system <NUM> of <FIG> and is described with continued reference to <FIG> and <FIG>. A controller <NUM> can interface with the motor drive electronics 214A, 214B, rectifier electronics 215A, 215B, energy storage management system <NUM>, integrated fuel control unit <NUM>, spool coupling system <NUM>, and/or other components (not depicted) of the hybrid electric propulsion system <NUM>. In embodiments, the controller <NUM> can control and monitor for fault conditions of the gas turbine engine <NUM> and/or the electrical power system <NUM>. For example, the controller <NUM> can be integrally formed or otherwise in communication with a full authority digital engine control (FADEC) of the gas turbine engine <NUM>. In embodiments, the controller <NUM> can include a processing system <NUM>, a memory system <NUM>, and an input/output interface <NUM>. The controller <NUM> can also include various operational controls, such as a spool coupling control <NUM> that controls the activation/deactivation of the spool coupling system <NUM> and/or other hybrid electric system control effectors <NUM> further described herein.

The processing system <NUM> can include any type or combination of central processing unit (CPU), including one or more of: a microprocessor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. The memory system <NUM> can store data and instructions that are executed by the processing system <NUM>. In embodiments, the memory system <NUM> may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable medium onto which is stored data and algorithms in a non-transitory form. The input/output interface <NUM> is configured to collect sensor data from the one or more system sensors and interface with various components and subsystems, such as components of the motor drive electronics 214A, 214B, rectifier electronics 215A, 215B, energy storage management system <NUM>, integrated fuel control unit <NUM>, spool coupling system <NUM>, and/or other components (not depicted) of the hybrid electric propulsion system <NUM>. The controller <NUM> provides a means for controlling the hybrid electric system control effectors <NUM> using a spool coupling control <NUM> that can be dynamically updated during operation of the hybrid electric propulsion system <NUM>. The means for controlling the hybrid electric system control effectors <NUM> can be otherwise subdivided, distributed, or combined with other control elements.

The controller <NUM> with spool coupling control <NUM> can apply control laws and access/update models to determine how to control and transfer power between the low speed spool <NUM> and high speed spool <NUM>. For example, sensed and/or derived parameters related to speed, flow rate, pressure ratios, temperature, thrust, and the like can be used to establish operational schedules and transition limits to maintain efficient operation of the gas turbine engine <NUM>. For instance, a mode of operation of the gas turbine engine <NUM>, such as idle, takeoff, climb, cruise, and descent can have different power settings, thrust requirements, flow requirements, and temperature effects. The spool coupling control <NUM> controls an electro-mechanical actuator <NUM> of the spool coupling system <NUM> that enables engagement/disengagement of clutch <NUM> when the electro-mechanical actuator <NUM> is activated. The spool coupling control <NUM> can determine when the spool coupling system <NUM> should be activated to prevent engagement and mechanical linking of the low speed spool <NUM> and the high speed spool <NUM> under other conditions where such linkage may be less desirable.

Referring now to <FIG>, plot <NUM> graphically illustrates a relationship between speeds of low speed spool <NUM> and a high speed spool <NUM> to support cross-spool coupling in a gas turbine engine, such as the gas turbine engine <NUM>, <NUM> of <FIG> and <FIG>. In this example, ground operation <NUM> (through take-off <NUM>) and in-flight operation <NUM> plots depict relationships between a speed <NUM> of the low speed spool <NUM> and a speed <NUM> of the high speed spool <NUM>. As can be seen in the example of <FIG>, changes in the speed <NUM> of the low speed spool <NUM> and the speed <NUM> of the high speed spool <NUM> are typically non-linear over a range of operating speeds where the low speed spool <NUM> and the high speed spool <NUM> are not mechanically coupled together. Above idle <NUM>, the ground operation <NUM> and in-flight operation <NUM> substantially overlap. The in-flight operation <NUM> can deviate from the ground operation <NUM> below idle <NUM> in approaching a windmill condition <NUM>. A coupled gear ratio <NUM> can define a linear relationship between the speed <NUM> of the low speed spool <NUM> and the speed <NUM> of the high speed spool <NUM> as implemented in the gear train <NUM> of <FIG>. When the spool coupling system <NUM> is activated and engaged at or below idle <NUM>, the in-flight operation <NUM> deviates from windmill condition <NUM> toward a geared windmill condition <NUM>. The geared windmill condition <NUM> has a higher value of speed <NUM> of the high speed spool <NUM> at a lower value of speed <NUM> of the low speed spool <NUM>. This can increase margin against the high speed spool <NUM> becoming locked at windmill conditions following an engine shutdown. Further, the spool coupling system <NUM> can improve in-flight start capability in windmill conditions and enable more reliable quick-relights. The spool coupling system <NUM> may also improve starter assisted start capability in windmill conditions when used in combination with one or more of the electric motors 212A, 212B, for example.

Referring now to <FIG>, plot <NUM> graphically illustrates a relationship between speeds of low speed spool <NUM> and a high speed spool <NUM> to support cross-spool coupling in a gas turbine engine, such as the gas turbine engine <NUM>, <NUM> of <FIG> and <FIG>. Plot <NUM> is an example of an in-flight shutdown and restart scenario. In-flight operation <NUM> depicts a relationship between a speed <NUM> of the low speed spool <NUM> and a speed <NUM> of the high speed spool <NUM>. Below idle <NUM>, the in-flight operation <NUM> is non-linear approaching a windmill condition <NUM>. A coupled gear ratio <NUM> can define a linear relationship between the speed <NUM> of the low speed spool <NUM> and the speed <NUM> of the high speed spool <NUM> as implemented in the gear train <NUM> of <FIG>. A spool coupling activation condition <NUM> can define a threshold for activating or deactivating the spool coupling system <NUM>, where the spool coupling system <NUM> engages at an engagement condition <NUM>. The spool coupling activation condition <NUM> can be defined below idle <NUM> and above the engagement condition <NUM>. The engagement condition <NUM> can be an alignment point where the in-flight operation <NUM> intersects the coupled gear ratio <NUM> before reaching the windmill condition <NUM>. When the spool coupling system <NUM> is activated and engaged at or below idle <NUM>, the in-flight operation <NUM> deviates from windmill condition <NUM> toward a geared windmill condition <NUM>. The geared windmill condition <NUM> has a higher value of speed <NUM> of the high speed spool <NUM> at a lower value of speed <NUM> of the low speed spool <NUM>.

As the gas turbine engine <NUM>, <NUM> is shut down from idle or above, the clutch <NUM> is activated (although not yet engaged) as the low speed spool <NUM> (or high speed spool <NUM>) transitions below idle <NUM> while the speed <NUM> of the high speed spool <NUM> is still above the level of the coupled gear ratio <NUM>. As the speeds <NUM>, <NUM> continue to decrease, the high speed spool <NUM> will naturally approach the level of the coupled gear ratio <NUM> and engage the clutch <NUM> at which point the low speed spool <NUM> is transferring power to the high speed spool <NUM> to maintain the fixed coupled gear ratio of the gear train <NUM>. As the speeds <NUM>, <NUM> continue to decrease the spools <NUM>, <NUM> will maintain the coupled gear ratio <NUM> until a stabilized condition is reached with some fan windmill power being transferred to the high speed spool <NUM>, resulting in a lower windmill speed of the low speed spool <NUM> but a higher high speed of the high speed spool <NUM>. During an in-flight start, the low speed spool <NUM> will continue to supply power to the high speed spool <NUM> up until the point of clutch <NUM> disengagement as the speed <NUM> of the high speed spool <NUM> naturally increases beyond the level of the coupled gear ratio <NUM>, then the spool coupling system <NUM> de-activates to ensure the clutch <NUM> does not re-engage above idle <NUM>.

Referring now to <FIG>, plot <NUM> graphically illustrates a relationship between speeds of low speed spool <NUM> and a high speed spool <NUM> to support cross-spool coupling in a gas turbine engine, such as the gas turbine engine <NUM>, <NUM> of <FIG> and <FIG>. Plot <NUM> is an example of low-spool power assisted idle. In-flight operation <NUM> depicts a relationship between a speed <NUM> of the low speed spool <NUM> and a speed <NUM> of the high speed spool <NUM>. Below idle <NUM>, the in-flight operation <NUM> is non-linear. A coupled gear ratio <NUM> can define a linear relationship between the speed <NUM> of the low speed spool <NUM> and the speed <NUM> of the high speed spool <NUM> as implemented in the gear train <NUM> of <FIG>. Under normal conditions, power-assist to the low speed spool <NUM> at idle <NUM> will result in lower fuel flow (or none if the gas turbine engine <NUM> is completely externally powered) and a lower (sub-idle) speed <NUM> of the high speed spool <NUM>. Utilizing the spool coupling system <NUM>, the high speed spool <NUM> can be forced up to the normal speed of idle <NUM> as geared low spool power-assisted idle <NUM> even though there is less or no fuel flow. When the power assist (e.g., electric motor 212A) is removed or a restart is desired, the engine spools <NUM>, <NUM> are already at the idle condition, resulting in no delay in achieving idle <NUM>, compared with a restart time if no spool coupling was utilized at low spool power-assisted idle <NUM>.

Referring now to <FIG> with continued reference to <FIG>, <FIG> is a flow chart illustrating a method <NUM> for providing selective spool coupling, in accordance with an embodiment. The method <NUM> may be performed, for example, by the gas turbine engine <NUM> of <FIG>, the hybrid electric propulsion system <NUM> of <FIG>, or other such configurations that include the spool coupling system <NUM>. For purposes of explanation, the method <NUM> is described primarily with respect to the hybrid electric propulsion system <NUM> of <FIG>; however, it will be understood that the method <NUM> can be performed on other configurations (not depicted).

Method <NUM> pertains to the controller <NUM> executing embedded code for the spool coupling control <NUM> along with other control functions. At block <NUM>, the controller <NUM> can determine a mode of operation of a gas turbine engine <NUM> that includes a low speed spool <NUM> and a high speed spool <NUM>. The mode of operation can be determined based on a thrust command, operating parameters, sensed values, and/or other factors known in the art. The mode of operation of the gas turbine engine <NUM> can distinguish between ground-based operation and flight operation.

At block <NUM>, the controller <NUM> can monitor for a spool coupling activation condition associated with the mode of operation. The spool coupling activation condition can include detecting a reduction in speed of the low speed spool <NUM> below an idle condition prior to a windmill condition while the mode of operation is an in-flight mode.

At block <NUM>, the controller <NUM> can activate a spool coupling system <NUM> based on the controller <NUM> detecting the spool coupling activation condition. At block <NUM>, engagement and power transfer between the low speed spool <NUM> and the high speed spool <NUM> can occur based on activation of the spool coupling system <NUM> and reaching an engagement condition of the spool coupling system <NUM>. The spool coupling system <NUM> is configured to mechanically link the low speed spool <NUM> and the high speed spool <NUM>. The engagement condition of the spool coupling system <NUM> can include a gear ratio level of the spool coupling system <NUM> aligning with a ratio of high speed spool <NUM> speed to low speed spool <NUM> speed. A stabilization condition can be reached after engagement of the spool coupling system <NUM>, resulting in fan windmill power being transferred to the high speed spool <NUM>.

At block <NUM>, disengagement of the spool coupling system <NUM> occurs based on the gas turbine engine <NUM> reaching a disengagement condition. At block <NUM>, the controller <NUM> can deactivate the spool coupling system <NUM> to prevent reengagement of the spool coupling system <NUM> above the spool coupling activation condition. The low speed spool <NUM> can provide power to the high speed spool <NUM> until the spool coupling system <NUM> reaches the disengagement condition, and the spool coupling system <NUM> can be deactivated to prevent reengagement of the spool coupling system <NUM> above the spool coupling activation condition.

In some embodiments, the mode of operation of the gas turbine engine is a sub-idle mode that activates, engages, disengages, and deactivates the spool coupling system below an idle level of operation of the gas turbine engine during flight. Further, the mode of operation of the gas turbine engine <NUM> can be a low spool power-assisted idle that results in the high speed spool <NUM> at idle when the spool coupling system <NUM> is engaged. The spool coupling system <NUM> can include a variable transmission system with multiple gear ratios and multiple levels of spool power transfer and engagement speeds.

Also, it is clear to one of ordinary skill in the art that, the stability enhancement provided by the dynamic torque and power capability of the coupled electric motor system described herein can be combined with and enhance other surge control features, such as surge control valves, variable stators, and fuel flow control.

Claim 1:
A system comprising:
a gas turbine engine (<NUM>;<NUM>) comprising a low speed spool (<NUM>) and a high speed spool (<NUM>);
a spool coupling system (<NUM>) comprising an electro-mechanical actuator (<NUM>) and a clutch (<NUM>) configured to mechanically link the low speed spool (<NUM>) and the high speed spool (<NUM>); and
a controller (<NUM>) operable to:
determine a mode of operation of the gas turbine engine (<NUM>; <NUM>);
monitor for a spool coupling activation condition associated with the mode of operation;
activate the electro-mechanical actuator (<NUM>) of the spool coupling system (<NUM>) based on the controller (<NUM>) detecting the spool coupling activation condition, wherein engagement of the clutch (<NUM>) and power transfer between the low speed spool (<NUM>) and the high speed spool (<NUM>) occurs based on activation of the electro-mechanical actuator (<NUM>) of the spool coupling system (<NUM>) and reaching an engagement condition of the clutch (<NUM>) of the spool coupling system; and
deactivate the electro-mechanical actuator (<NUM>) of the spool coupling system (<NUM>) after disengagement of the clutch (<NUM>) to prevent reengagement of the spool coupling system above the spool coupling activation condition, wherein disengagement of the clutch of the spool coupling system (<NUM>) occurs based on the gas turbine engine (<NUM>; <NUM>) reaching a disengagement condition of the clutch (<NUM>).