Patent Description:
Aircraft typically utilize brake systems on wheels to slow or stop the aircraft during landings, taxiing and emergency situations, such as, for example, a rejected take off (RTO), which generally refers to engagement of a brake system during an aborted take off and involves high braking loads over a short time period, resulting in a rapid increase in the brake temperature. The brake systems generally employ a heat sink comprising a series of friction disks, sandwiched between a pressure plate and an end plate, that may be forced into sliding contact with one another during a brake application to slow or stop the aircraft.

A typical hydraulic brake system may include, without limitation, a source of pressurized hydraulic fluid, a hydraulic actuator for exerting a force across the heat sink (e.g., across the pressure plate, the series of friction disks and the end plate), a valve for controlling a pressure level provided to the hydraulic actuator and a brake control unit for receiving inputs from a pilot and from various feedback mechanisms and for producing responsive outputs to the valve. Upon activation of the brake system (e.g., by depressing a brake pedal), a pressurized fluid is applied to the hydraulic actuator, which may comprise a piston configured to translate the pressure plate toward the end plate. A typical electric brake system includes various electromechanical counterparts to a hydraulic brake system, such as, for example, an electromechanical brake actuator (EBA) in place of the hydraulic actuator and a source of electric power in place of the source of pressurized hydraulic fluid.

<CIT> describes a braking system for use in safely reducing the speed and stopping movement of vehicles by minimizing brake failure due to heat build-up and by providing auxiliary braking capacity.

<CIT> describes a system comprising an aircraft having a landing gear comprising a wheel, a friction brake having a brake material coupled to the wheel, a regenerative brake comprising a reversible taxi motor coupled to the wheel, a sensor configured to measure a wheel parameter of the wheel and a temperature of the friction brake, and a tangible, non-transitory memory configured to communicate with a controller.

In accordance with an aspect of the present invention, there is provided a braking system for an aircraft. The braking system comprises: a brake assembly; a hydraulic braking subsystem having a hydraulic brake actuator configured to operate the brake assembly; an electric braking subsystem having an electric brake actuator configured to operate the brake assembly; a hydraulic brake control unit configured to operate the hydraulic braking subsystem; and an electric brake control unit configured to operate the electric braking subsystem, the electric brake control unit in operable communication with the hydraulic brake control unit, wherein the braking system is configured to: determine a primary braking system for a prior flight cycle; and activate the electric braking subsystem to be the primary braking system for a current flight cycle in response to determining the hydraulic braking subsystem was the primary braking system for the prior flight cycle.

In various embodiments, only the primary braking system is configured to operate the brake assembly for a flight cycle.

In various embodiments, the electric brake control unit and the hydraulic brake control unit are both configured to receive an indication that the braking system has been powered up prior to determining the primary braking system for the prior flight cycle.

In various embodiments, the electric brake control unit is configured to command the hydraulic brake control unit to be the primary braking system for the current flight cycle in response to determining the electric braking subsystem was the primary braking system for the prior flight cycle.

In various embodiments, the primary braking system is further configured to: determine a take off phase of the current flight cycle; and activate a secondary braking system for potential use during the take off phase of the current flight cycle. The primary braking system may be further configured to determine a rejected take off (RTO) phase of the current flight cycle. The primary braking system may be further configured to command the hydraulic braking subsystem and the electric braking subsystem to operate the brake assembly in response to determining the RTO phase of the current flight cycle. The primary braking system may be further configured to command only the primary braking system to operate the brake assembly during the RTO phase of the current flight cycle. The primary braking system may be further configured to determine a failure of the primary braking system during the RTO phase of the current flight cycle. The primary braking system may be further configured to command the secondary braking system to take over braking controls in response to determining the failure of the primary braking system.

The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present invention, however, may best be obtained by referring to the following detailed description and claims in connection with the following drawings.

While these various embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that changes may be made without departing from the scope of the invention.

Methods for avoiding latent brake failure, as well as methods of mitigating latent brake failure, are disclosed herein.

Referring now to <FIG>, an aircraft <NUM> includes multiple landing gear systems, including a first landing gear <NUM> (or a port-side landing gear), a second landing gear <NUM> (or a nose landing gear) and a third landing gear <NUM> (or a starboard-side landing gear). The first landing gear <NUM>, the second landing gear <NUM> and the third landing gear <NUM> each include one or more wheel assemblies. For example, the third landing gear <NUM> includes an inner wheel assembly <NUM> and an outer wheel assembly <NUM>.

The first landing gear <NUM>, the second landing gear <NUM> and the third landing gear <NUM> support the aircraft <NUM> when the aircraft <NUM> is not flying, thereby enabling the aircraft <NUM> to take off, land and taxi without incurring damage. In various embodiments, one or more of the first landing gear <NUM>, the second landing gear <NUM> and the third landing gear <NUM> is operationally retractable into the aircraft <NUM> while the aircraft <NUM> is in flight.

In various embodiments, the aircraft <NUM> further includes an avionics unit <NUM>, which includes one or more controllers (e.g., processors) and one or more tangible, non-transitory memories capable of implementing digital or programmatic logic. In various embodiments, for example, the one or more controllers are one or more of a general purpose processor, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate array (FPGA) or other programmable logic device, discrete gate, transistor logic, or discrete hardware component, or any of various combinations thereof or the like. In various embodiments, the avionics unit <NUM> controls operation of various components of the aircraft <NUM>. For example, the avionics unit <NUM> controls various parameters of flight, such as an air traffic management systems, auto-pilot systems, auto-thrust systems, crew alerting systems, electrical systems, electronic checklist systems, electronic flight bag systems, engine systems flight control systems, environmental systems, hydraulics systems, lighting systems, pneumatics systems, traffic avoidance systems, trim systems, brake systems and the like.

In various embodiments, the aircraft <NUM> further includes brake control units (BCUs) <NUM> (e.g., hydraulic brake control unit <NUM> and electric brake control unit <NUM> as described further herein). With brief reference now to <FIG>, the BCUs <NUM> include one or more controllers <NUM> (e.g., processors) and one or more memories <NUM> (e.g., tangible, non-transitory memories) capable of implementing digital or programable logic. In various embodiments, for example, the one or more controllers <NUM> is one or more of a general purpose processor, DSP, ASIC, FPGA, or other programmable logic device, discrete gate, transistor logic, or discrete hardware component, or any of various combinations thereof or the like, and the one or more memories <NUM> is configured to store instructions that are implemented by the one or more controllers <NUM> for performing various functions, such as adjusting the hydraulic pressure or electric power provided to a brake actuator depending on the degree of braking desired. In various embodiments, the BCUs <NUM> control the braking of the aircraft <NUM>. For example, the BCUs <NUM> control various parameters of braking, such as manual brake control, automatic brake control, antiskid braking, locked wheel protection, touchdown protection, emergency/parking brake monitoring or gear retraction braking. The BCUs <NUM> may further include hardware <NUM> capable of performing various logic using discrete power signals received from various aircraft systems. Referring again to <FIG>, the aircraft <NUM> further includes one or more brake assemblies coupled to each wheel assembly. For example, a brake assembly <NUM> is coupled to the outer wheel assembly <NUM> of the third landing gear <NUM> of the aircraft <NUM>. During operation, the brake assembly <NUM> applies a braking force to the outer wheel assembly <NUM> upon receiving a brake command from the BCUs <NUM>. In various embodiments, the outer wheel assembly <NUM> of the third landing gear <NUM> of the aircraft <NUM> (or of any of the other landing gear described above and herein) comprises any number of wheels or brake assemblies.

Referring now to <FIG>, schematic details of the brake assembly <NUM> illustrated in <FIG> are provided. In various embodiments, the brake assembly <NUM> is mounted on an axle <NUM> for use with a wheel <NUM> disposed on and configured to rotate about the axle <NUM> via one or more bearing assemblies <NUM>. A central axis <NUM> extends through the axle <NUM> and defines a center of rotation of the wheel <NUM>. A torque plate barrel <NUM> (sometimes referred to as a torque tube or barrel or a torque plate) is aligned concentrically with the central axis <NUM>, and the wheel <NUM> is rotatable relative to the torque plate barrel <NUM>. The brake assembly <NUM> includes an actuator ram assembly <NUM>, a pressure plate <NUM> disposed adjacent the actuator ram assembly <NUM>, an end plate <NUM> positioned a distal location from the actuator ram assembly <NUM>, and a plurality of rotor disks <NUM> interleaved with a plurality of stator disks <NUM> positioned intermediate the pressure plate <NUM> and the end plate <NUM>. The pressure plate <NUM>, the plurality of rotor disks <NUM>, the plurality of stator disks <NUM> and the end plate <NUM> together form a brake heat sink or brake stack <NUM>. The pressure plate <NUM>, the end plate <NUM> and the plurality of stator disks <NUM> are mounted to the torque plate barrel <NUM> and remain rotationally stationary relative to the axle <NUM>. The plurality of rotor disks <NUM> is mounted to the wheel <NUM> and rotate with respect to each of the pressure plate <NUM>, the end plate <NUM> and the plurality of stator disks <NUM>.

An actuating mechanism for the brake assembly <NUM> includes a plurality of actuator ram assemblies, including the actuator ram assembly <NUM>, circumferentially spaced around a piston housing <NUM> (only one actuator ram assembly is illustrated in <FIG>). Upon actuation, the plurality of actuator ram assemblies affects a braking action by urging the pressure plate <NUM> and the plurality of stator disks <NUM> into frictional engagement with the plurality of rotor disks <NUM> and against the end plate <NUM>. Through compression of the plurality of rotor disks <NUM> and the plurality of stator disks <NUM> between the pressure plate <NUM> and the end plate <NUM>, the resulting frictional contact slows or stops or otherwise prevents rotation of the wheel <NUM>. In various embodiments, the plurality of rotor disks <NUM> and the plurality of stator disks <NUM> are fabricated from various materials, such as, for example, ceramic matrix composite materials, that enable the brake disks to withstand and dissipate the heat generated during and following a braking action. As discussed in further detail below, in various embodiments, the actuator ram assemblies comprise a combination of electrically operated actuator rams (or electric brake actuators) and hydraulically operated actuator rams (or hydraulic brake actuators).

Referring now to <FIG>, a braking system <NUM> (or a redundant braking system or a hybrid braking system) is illustrated, in accordance with various embodiments. Generally, the braking system <NUM> may be separated into a hydraulic braking subsystem <NUM> and an electric braking subsystem <NUM>. Referring first to the hydraulic braking subsystem <NUM>, the braking system <NUM> includes a hydraulic brake control unit <NUM>, which is programmed to control the various braking functions performed by the hydraulic braking subsystem <NUM>. The hydraulic braking subsystem <NUM> includes a hydraulic power source <NUM> configured to provide a hydraulic fluid to a primary brake control module <NUM> via a primary hydraulic line <NUM>. A primary pressure transducer <NUM> senses the pressure of the hydraulic fluid and provides a signal reflective of the pressure to the hydraulic brake control unit <NUM> via a data circuit <NUM>. In various embodiments, the hydraulic braking subsystem <NUM> includes a hydraulic fluid return <NUM> that is configured to return hydraulic fluid from the primary brake control module <NUM> to the hydraulic power source <NUM> via a return hydraulic line <NUM>. A secondary hydraulic line <NUM> fluidly couples the primary brake control module <NUM> to a brake assembly <NUM>, similar to the brake assembly <NUM> described above with reference to <FIG>. More particularly, the secondary hydraulic line <NUM> is fluidly coupled to a hydraulic brake actuator <NUM> (or a plurality of hydraulic brake actuators) housed within the brake assembly <NUM>. In various embodiments, a fuse <NUM> is fluidly coupled to the secondary hydraulic line <NUM> downstream of the primary brake control module <NUM>. The fuse <NUM> acts as a shut-off valve or switch in the event the secondary hydraulic line <NUM> experiences a loss of pressure - e.g., in the event of a leak in the secondary hydraulic line <NUM> or the brake assembly <NUM> - thereby preventing hydraulic fluid from continuing to flow to the secondary hydraulic line <NUM> and leaking out of the hydraulic system. A secondary pressure transducer <NUM> is fluidly coupled to the secondary hydraulic line <NUM> and electrically coupled to the hydraulic brake control unit <NUM> via the data circuit <NUM>. In the event the secondary pressure transducer <NUM> senses a loss of pressure within the secondary hydraulic line <NUM>, the hydraulic brake control unit <NUM> may, in redundant fashion, pass control of the braking system <NUM> to the electric braking subsystem <NUM>. As illustrated, the secondary hydraulic line <NUM>, the fuse <NUM>, the secondary pressure transducer <NUM> and the brake assembly <NUM> are replicated for each of a plurality of outer wheel assemblies <NUM> and for each of a plurality of inner wheel assemblies <NUM> comprised within the braking system <NUM>. Without loss of generality, in various embodiments, the hydraulic braking subsystem <NUM> also includes wheel speed transducers and brake temperature sensors, such as, for example, an inboard wheel speed transducer <NUM> and an outboard wheel speed transducer <NUM>, and an inboard brake temperature sensor <NUM> and an outboard brake temperature sensor <NUM>.

Referring now to the electric braking subsystem <NUM>, the braking system <NUM> includes an electric brake control unit <NUM>, which is programmed to control the various braking functions performed by the electric braking subsystem <NUM>. The electric braking subsystem <NUM> includes an electric power source <NUM> configured to provide electric power to an electric brake actuator controller <NUM>, which, for example, may be an inboard electric brake actuator controller or an outboard electric brake actuator controller. The electric power is provided to the electric brake actuator controller <NUM> via an electric power circuit <NUM>. The electric brake actuator controller <NUM> is electrically coupled to an electric brake actuator <NUM> (or a plurality of electric brake actuators) that is housed within the brake assembly <NUM>. In various embodiments, the electric brake actuator controller <NUM> includes or is connected to a control circuitry <NUM> configured to monitor various aspects of a braking operation. The electric brake actuator <NUM> may include, for example, a load cell <NUM> electrically coupled to the control circuitry <NUM> and configured to monitor the load applied via the electric brake actuator <NUM>. In various embodiments, the electric brake control unit <NUM> provides force commands to the electric brake controller <NUM>, which in turn provides a current command to the electric brake actuator <NUM> to apply force, directing the electric brake actuator <NUM> to cause the brake assembly <NUM> to mechanically operate, thereby driving the brake assembly <NUM> to provide braking power. In various embodiments, the brake actuator controller <NUM> monitors the load cell <NUM> (e.g., via the control circuitry <NUM>) to apply more or less current to achieve a desired force. In various embodiments, the electric brake actuator controller <NUM> is coupled to the electric brake control unit <NUM> via a communication link <NUM>. The communication link <NUM> may comprise, for example, a controller area network bus <NUM>. Similar to the hydraulic braking subsystem <NUM>, and without loss of generality, the electric braking subsystem <NUM> also includes wheel speed transducers, such as, for example, an inboard wheel speed transducer <NUM> and an outboard wheel speed transducer <NUM>, or brake temperature sensors.

Referring now to <FIG>, the brake assembly <NUM> is described with further detail. As illustrated, the brake assembly <NUM> includes a pressure plate <NUM> configured to apply a compressive load against a brake stack or heat sink, which includes a plurality of brake rotors and a plurality of brake stators sandwiched between the pressure plate and an end plate. As described above, the brake assembly <NUM> includes the hydraulic brake actuator <NUM> (or a plurality of such hydraulic brake actuators) and the electric brake actuator <NUM> (or a plurality of such electric brake actuators). In various embodiments, the brake assembly <NUM> includes four electric brake actuators spaced at ninety degree (<NUM>°) intervals about the pressure plate <NUM> and four hydraulic brake actuators spaced at ninety degree (<NUM>°) intervals about the pressure plate <NUM>, with each electric brake actuator and each hydraulic brake actuator spaced at forty-five degree (<NUM>°) intervals. Fewer or greater numbers of actuators, both electric and hydraulic, are contemplated within the scope of the invention.

Referring back to <FIG>, during operation, a pilot or a co-pilot depresses a pilot brake pedal <NUM> or a co-pilot brake pedal <NUM>, each of which is connected to a hydraulic brake position sensor <NUM> and to an electric brake position sensor <NUM>. The hydraulic brake position sensor <NUM> generates a signal reflective of the pedal position that is transmitted to the hydraulic brake control unit <NUM> via a hydraulic brake sensor bus <NUM>. The hydraulic brake control unit <NUM>, if employed, then activates the hydraulic brake actuator <NUM> based on a current signal that is transmitted to the primary brake control module <NUM> via a primary brake control bus <NUM>. Similarly, the electric brake position sensor <NUM> generates a signal reflective of the pedal position that is transmitted to the electric brake control unit <NUM> via an electric brake sensor bus <NUM>. The electric brake control unit <NUM>, if employed, then activates the electric brake actuator <NUM> based on a force request that is transmitted to the electric brake actuator controller <NUM> via the communication link <NUM>. In various embodiments, an avionics system <NUM> is configured to employ one or both of the hydraulic braking subsystem <NUM> and the electric braking subsystem <NUM> via signals transmitted over a respective data bus <NUM>. In various embodiments, an autobrake selector <NUM> is configured to employ one or both of the hydraulic braking subsystem <NUM> and the electric braking subsystem <NUM> via signals transmitted over an autobrake data bus <NUM>.

The braking system <NUM> may operate in a fully hydraulic mode, employing only the hydraulic braking subsystem <NUM>, or in a fully electric mode, employing only the electric braking subsystem <NUM>. In addition, the invention contemplates, in various embodiments, the hydraulic braking subsystem <NUM> being employed as the principal braking system, while the electric braking subsystem <NUM> is employed as a backup braking system in the event a failure occurs with the hydraulic braking subsystem <NUM>. The invention also contemplates, in various embodiments, the electric braking subsystem <NUM> being employed as a parking brake when the aircraft is at rest. In various embodiments, the hydraulic brake control unit <NUM> and the electric brake control unit <NUM> are configured to communicate with one another via an intercommunication bus <NUM>. Such communication enables, for example, transfer of control from the hydraulic brake control unit <NUM> to the electric brake control unit <NUM> following a failure of the hydraulic braking subsystem <NUM>. For example, in the event the hydraulic brake control unit <NUM> detects a leak of hydraulic fluid within the hydraulic braking subsystem <NUM>, the hydraulic brake control unit <NUM> may communicate with the electric brake control unit <NUM> and transfer control of the braking system <NUM> to the electric brake control unit <NUM>. Similarly, in the event the electric brake control unit <NUM> detects a failure within the electric braking subsystem <NUM>, the electric brake control unit <NUM> may communicate with the hydraulic brake control unit <NUM> and transfer control of the braking system <NUM> to the hydraulic brake control unit <NUM>. In this regard, a primary braking system and a secondary braking system may be determined for each flight cycle, as described further herein. Based on a failure to the primary braking system being detected, the BCUs <NUM> are configured to transfer control from the primary braking system to the secondary braking system. The above invention provides for a hybrid braking architecture. In various embodiments, the architecture employs hydraulic power for normal braking and electric power for an alternate braking system or a parking brake system. The architecture provides a fully redundant braking system for normal pedal operated braking and for emergency braking. In various embodiments, the piston housing (e.g., the piston housing <NUM> referred to in <FIG>) is modified to accept four hydraulic actuators and four electric actuators, spaced equally and alternating between one hydraulic actuator and one electric actuator; though any number of actuators is contemplated by the invention. The equal spacing of forty-five degrees (<NUM>°) between alternating hydraulic and electric brake actuators allows for uniform force application on the brake stack when the hydraulic system is active or the electric system is active.

In various embodiments, the architecture is operated using pedals in the cockpit. This allows seamless activity and minimum pilot effort when, for example, the emergency system is engaged. The architecture is transparent for actuation (e.g., automated), although crew-alerting system (CAS) messages may be employed to inform the pilot that the emergency system (e.g., the electric braking subsystem) has become active. The hydraulic and electric brake control units are in constant communication using, for example, controller area network (CAN) communication links, such that when the primary brake control unit (either the hydraulic or the electric brake control unit) detects a loss of braking or other fault, the alternate brake control unit (either the hydraulic or the electric brake control unit) may take over control and operate the braking. In various embodiments, a switch may also be provided in the cockpit to allow the pilot to manually switch from the one braking subsystem to the other - e.g., the hydraulic subsystem to the electric sub system - depending on the failure and any other issues or faults occurring with the power supplies or other aircraft system degradations.

Referring now to <FIG>, a process <NUM> for operating the braking system <NUM> is described, in accordance with various embodiments. The process <NUM> starts in response to the braking system <NUM> powering up (block <NUM>). Once an aircraft <NUM> is parked at a gate, and a parking brake is set, aircraft engines, and the BCUs <NUM> may be powered down. Once the aircraft <NUM> is loaded with passengers and all maintenance checks have been performed, a pilot turns back on the BCUs <NUM> and the aircraft engines. In response to powering up the braking system <NUM> via the BCUs <NUM> (i.e., the hydraulic brake control unit <NUM> and the electric brake control unit <NUM>), the process <NUM> is initiated.

The process <NUM> further comprises determining which brake subsystem (e.g., hydraulic braking subsystem <NUM> or electric braking subsystem <NUM>) was active during a prior flight cycle (step <NUM>). Stated another way, the BCUs <NUM> (i.e., the hydraulic brake control unit <NUM> and the electric brake control unit <NUM>), prior to powering down a previous flight cycle, store (e.g., in the memory <NUM>) the braking subsystem utilized in the previous flight cycle. Thus, in response to powering up, the BCUs <NUM> determine if the previous active system was the hydraulic braking subsystem <NUM> in step <NUM>.

In response to determining the hydraulic braking subsystem <NUM> was utilized for the previous flight cycle, the BCUs <NUM> (e.g., via electric brake control unit <NUM>) activate the electric braking subsystem <NUM> as a primary brake system for a current flight cycle (step <NUM>). Similarly, in response to determining the electric braking subsystem <NUM> was utilized for the previous flight cycle, the BCUs <NUM> (e.g., via the hydraulic brake control unit <NUM>) activate the hydraulic braking subsystem <NUM> for the current flight cycle (step <NUM>). After selecting a primary brake system for sole use during the current flight cycle in step <NUM> or step <NUM>, the process <NUM> ends at step <NUM>.

Thus, the process <NUM> keeps track of which system (e.g., hydraulic braking subsystem <NUM> or electric braking subsystem <NUM>) was utilized for the previous flight cycle and alternates to the other subsystem for the following flight cycle. In this regard, the process <NUM> facilitates exercise of both systems (e.g., hydraulic braking subsystem <NUM> or electric braking subsystem <NUM>) frequently to avoid latent brake failures. The process <NUM> further allows use of the electric brake actuator <NUM> half of the time relative to conventional system, thus doubling the life of the electric braking subsystem <NUM>.

Referring now to <FIG>, a process <NUM> for operating the braking system <NUM> with the BCUs <NUM> during a rejected take off (RTO) phase of flight is illustrated, in accordance with various embodiments. The process <NUM> comprises determining, via a primary BCU of the BCUs <NUM> (e.g., the electric brake control unit <NUM> or the hydraulic brake control unit <NUM>, whichever is a primary brake control unit determined from process <NUM>), an aircraft <NUM> is in a take off flight phase. The primary BCU may make this determination based on receiving sensor data (e.g., from a weight on wheel sensor, a speed sensor, etc.). For example, the primary BCU may receive data from a weight on wheel sensor indicating wheel <NUM> has weight on the wheel <NUM>. In this regard, the primary BCU is able to determine the aircraft is on the ground. During take-off, an aircraft <NUM> has to reach an aircraft velocity to generate enough lift for the aircraft <NUM> to take off. Thus, in response to the aircraft <NUM> exceeding a speed threshold and having weight on wheels, the primary BCU is able to determine the aircraft <NUM> is in a take off flight phase. In various embodiments, the speed threshold for determining a take off phase of flight may be approximately <NUM> knots. However, the present invention is not limited in this regard, and one skilled in the art may recognized various aircraft speed thresholds for determining a take off phase of flight, in accordance with various embodiments.

The process <NUM> further comprises activating a secondary braking system in response to determining the aircraft <NUM> is in a take off phase of flight (step <NUM>). In this regard, as indicated in process <NUM> one of the hydraulic braking subsystem <NUM> or the electric braking subsystem <NUM> may be activated as a primary braking system for the flight cycle, and the remaining braking subsystem may be a secondary braking system for the flight cycle. During the take off phase, the secondary braking system may be activated in case the take-off must be aborted.

For example, the process <NUM> further comprises determining a rejected take off (RTO) flight phase (step <NUM>). In various embodiments, during a rejected take off (RTO) flight phase, a pilot may reduce an engine power provided to engines of the aircraft <NUM> to idle. In this regard, the primary BCU may receive an indication that the engine power provided to the engines of the aircraft <NUM> have been reduced to idle, while the aircraft is in a take off phase (e.g., determined from step <NUM>). Thus, the primary BCU may determine, based on a reduction of engine power to idle, that the aircraft <NUM> is in an RTO phase of flight.

The process <NUM> further comprises commanding, via the primary BCU, the primary braking system and the secondary braking system to apply braking (step <NUM>). In this regard, the process <NUM> may facilitate a boost in braking to a maximum potential for the braking system <NUM> to stop the aircraft <NUM> as quickly as possible during the RTO phase of flight.

Referring now to <FIG>, a process <NUM> for operating the braking system <NUM> with the BCUs <NUM> during a rejected take off (RTO) phase of flight is illustrated, in accordance with various embodiments. The process <NUM> includes steps <NUM>, <NUM>, and <NUM> of process <NUM>. However, the process <NUM> further comprises commanding braking via the primary braking system (e.g., hydraulic braking subsystem <NUM> or electric braking subsystem <NUM> selected from process <NUM> of <FIG>) only (step <NUM>). In this regard, the process <NUM> may continue to operate in accordance with the process <NUM> (i.e., utilize only a single braking system per flight cycle, including in an RTO event. In various embodiments, the process <NUM> further comprises determining, via the primary braking system, a latent failure of the primary braking system (step <NUM>). In various embodiments, the failure may be determined based on the primary BCU receiving a first wheel speed from a first wheel speed sensor, receiving a second wheel speed from a second wheel speed sensor, comparing the first wheel speed to the second wheel speed, and determining the first wheel speed is greater than the second wheel speed by a predetermined threshold. The predetermined threshold may be a wheel speed value or may be an error percentage or any other desired threshold depending on the particular arithmetic function used for detecting difference. The predetermined threshold may be a tunable parameter based upon the particular design of the braking system <NUM>. In various embodiments, the primary BCU may detect that the difference is greater than the predetermined threshold for at least a minimum duration to prevent a false alarm in response to a brief anomaly, such as a brief skid event for example. In various embodiments, the minimum duration is on the order of milliseconds. In various embodiments, the minimum duration is on the order of seconds. However, the minimum duration may be chosen to be any suitable duration that would indicate a high likelihood of a failed brake component.

In various embodiments, in response to determine the latent failure of the primary braking system in step <NUM>, the process <NUM> further comprises commanding braking via the secondary braking system (step <NUM>). In this regard, consistent braking may be applied to each wheel <NUM> on each main landing gear (e.g., first landing gear <NUM> and third landing gear <NUM>) during a RTO event, irrespective of a latent failure occurring in the primary braking system, in accordance with various embodiments.

However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the invention. The scope of the invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more.

After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the invention in alternative embodiments.

Numbers, percentages, or other values stated herein are intended to include that value, and also other values that are about or approximately equal to the stated value, as would be appreciated by one of ordinary skill in the art encompassed by various embodiments of the present invention. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable industrial process, and may include values that are within <NUM>%, within <NUM>%, within <NUM>%, within <NUM>%, or within <NUM>% of a stated value. Additionally, the terms "substantially," "about" or "approximately" as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the term "substantially," "about" or "approximately" may refer to an amount that is within <NUM>% of, within <NUM>% of, within <NUM>% of, within <NUM>% of, and within <NUM>% of a stated amount or value. Furthermore, no element, component, or method step in the present invention is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.

Claim 1:
A braking system (<NUM>) for an aircraft, comprising:
a brake assembly (<NUM>; <NUM>);
a hydraulic braking subsystem (<NUM>) having a hydraulic brake actuator (<NUM>) configured to operate the brake assembly (<NUM>; <NUM>);
an electric braking subsystem (<NUM>) having an electric brake actuator (<NUM>) configured to operate the brake assembly (<NUM>; <NUM>);
characterised by
a hydraulic brake control unit (<NUM>) configured to operate the hydraulic braking subsystem (<NUM>); and
an electric brake control unit (<NUM>) configured to operate the electric braking subsystem (<NUM>), the electric brake control unit (<NUM>) in operable communication with the hydraulic brake control unit (<NUM>), wherein the braking system (<NUM>) is configured to:
determine a primary braking system for a prior flight cycle; and
activate the electric braking subsystem (<NUM>) to be the primary braking system for a current flight cycle in response to determining the hydraulic braking subsystem (<NUM>) was the primary braking system for the prior flight cycle.