Patent Description:
The present invention concerns a method of operating an aircraft during taxiing, as claimed in appended claim <NUM>.

The invention also concerns an aircraft controller as claimed in claim <NUM>.

Conventional passenger aircraft use their engines to provide power for taxiing in a forwards direction at an airport. The engines are run at an idle (low) setting and aircraft brakes are used to decrease the speed to a suitable taxiing speed. If the aircraft is to be moved backwards, a tug or similar is used.

Various e-taxi systems have been described and proposed (for example, in <CIT>) where a landing gear drive system (comprising a motor, a drive gear connected to the motor, and a driven gear that can be driven by the drive gear and being connected to the wheel) is used to drive one or more wheels of a landing gear of an aircraft in a forwards or backwards direction. When taxiing using such an e-taxi system, it is proposed that the engines are turned off and the aircraft is driven using the e-taxi drive system only. The driving torque applied by the drive system is proportional to a cockpit command. When a pilot wishes to reduce the speed of the taxiing aircraft, they apply the aircraft brake. This would cause the e-taxi system to disengage (the drive gear and driven gear to be disconnected) so that the e-taxi motor is not caused to experience excessive heating and so that the loads on the wheel rims are reduced, during braking.

However, it is believed that this method may cause issues. In particular, it is considered that the handling qualities of the aircraft would be unsatisfactory, as the decrease of speed may not be smooth or predictable enough, due to the discontinuity when the e-taxi drive system is suddenly disconnected. For example, smooth control and speed predictability are required especially given the need to park the aircraft at a specific and precise location when approaching an airport gate or when the aircraft is taxiing in a queue behind other aircraft. It is also believed that stopping the aircraft during pushback would require smoother handling that what would be achieved with the proposed method. This is at least partly due to the fact that the brakes of the aircraft would be relatively cold when pushback is required and so may be especially jerky. In practice, this may mean that the aircraft has to be taxied at a lower speed than that of a conventional aircraft, if this precision manoeuvring is required. This would increase the turnaround time of the aircraft and could cause traffic issues at the airport. In addition, this would also require the pilot to control the aircraft using two control systems; that of the e-taxi drive system and the brake system.

<CIT> discloses an aircraft steering system using an aircraft ground taxi drive system whereby electrical power generated by a first motor-generator of a landing gear wheel drive system in a regenerative braking mode is supplied to a second motor-generator of a landing gear wheel drive system in a motorized driving mode, thus providing differential force on the left versus right wheels. <CIT> discloses an aircraft taxi control system including a left and right main gear drive motors, and left (and right) motor drive controllers which produce left (and right) motor torque signals in dependence on nose gear angle and nose wheel speed, with the aim of reducing lateral loading of the nose wheel during a turning manoeuvre. <CIT> discloses an aircraft electric taxi system including a speed computer coupled to a ground speed sensor and to a speed selection unit, and a motor controller which controls the speed of a wheel motor in response to a speed error signal produced by the speed computer. Left and right brakes may be applied and left and right wheel motors released selectively in response to left and right brake commands. Torque from the wheel motors may be re-applied automatically once the brakes are released.

The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method of operating an aircraft and/or an improved aircraft controller.

The present invention provides, according to a first aspect, a method of operating an aircraft during taxiing, the aircraft having a landing gear drive system for providing driving torque during taxiing, a landing gear brake system for providing braking torque during taxiing, and a brake command device with a plurality of different command levels over a brake command range, the method comprising the steps of, i) during a non-braking time period, taxiing the aircraft by using driving torque provided by the landing gear drive system, and not providing a braking torque from the landing gear brake system, ii) during a braking time period, providing the brake command device at one or more command levels within a sub-range of the brake command range, and controlling the landing gear drive system, in response to the level of the brake command device, to reduce the driving torque provided from that in step i) to a lower yet still positive driving torque.

In other words, the method involves a step ii) where the driving torque is reduced from the previous (non-braking) level, but still is more than zero. This may provide a "transition" step where, before braking torque is applied, the driving torque is reduced. This may additionally or alternatively provide a "combination" step where, braking torque is applied and the driving torque is reduced. This allows the aircraft to have a smoother and more predictable speed control and so enable effective parking, queuing (and pushback) etc. at the same speed as that used for conventional aircraft. This can also be achieved using only the brake command device. There is no need to disengage or turn off the e-taxi system prior to changing the level of the brake command device. The driving torque applied is reduced only in response to the braking command provided by the brake command device. This method also allows the aircraft to be controlled using the same techniques (i.e. just using the brake command device) as for a conventional aircraft that is taxied with the engines.

By providing a method where the drive system and brake system are somewhat integrated (i.e. they both are able to be working at the same time), the inventor has realised that good handling qualities can be achieved.

The landing gear drive system may be provided in a main landing gear or a nose landing gear, but preferably a main landing gear.

Preferably, a magnitude of reduction of the driving torque increases as the command level within the sub-range increases. In other words, the magnitude of driving torque provided decreases as the command level within the sub-range increases. For example, as there is more brake command from the brake command device (a pilot pressing harder on a brake pedal, for example), the less driving torque is applied.

The magnitude of reduction of the driving torque may increase linearly as the command level within the sub-range increases.

Preferably, in step i), there is either zero command level from the brake command device or a very low command level from the brake command device. In other words, step i) occurs where there is either no brake command or only a very low brake command (a pilot pressing very lightly or not at all on a brake pedal, for example). For example, the brake command may be up to <NUM>% of the total brake command possible. For example, the pilot may apply pressure to have a deflection of the brake pedal up to a <NUM>% of the maximum deflection of the brake pedal. In step i), the brake command may be up to between <NUM> and <NUM>% of the total brake command possible.

Preferably, step ii) occurs during a "transition" braking time period and wherein the brake command device is provided at one or more command levels within a "transition" sub-range of the brake command range. In this "transition" step, the driving torque is reduced to achieve a speed reduction of the aircraft but braking torque is not applied. This helps to "transition" from a pure driving mode to a mode where braking torque is applied. This also increases the effective range of the brake command device. This also ensures that the magnitude of driving torque that is combined with a braking torque (that is later applied) is limited to that below the maximum driving torque magnitude.

More preferably, the "transition" sub-range represents command levels at a low command level from the brake command device. In other words, step ii) occurs where there is a low brake command (a pilot pressing relatively lightly on a brake pedal, for example). For example, the brake command may be between <NUM>% and <NUM>% of the total brake command possible. For example, the pilot may apply pressure to have a deflection of the brake pedal of <NUM>% of the maximum deflection of the brake pedal. In step ii), the brake command may be between <NUM> and <NUM>% of the total brake command possible.

Alternatively, step ii) occurs during a "combination" braking time period and wherein the brake command device is provided at one or more command levels within a "combination" sub-range of the brake command range, and wherein step ii) comprises controlling the landing gear brake system, in response to the level of the brake command device, to provide a braking torque from the landing gear brake system. In this "combination" step, the driving torque is reduced to achieve a speed reduction of the aircraft and braking torque is also applied to further reduce the aircraft speed. This helps to provide an effective braking mode.

Preferably, the "combination" sub-range represents command levels at a medium command level from the brake command device. In other words, step ii) occurs where there is a medium brake command (a pilot pressing with reasonable pressure on a brake pedal, for example). For example, the brake command may be between <NUM>% and <NUM>% of the total brake command possible. For example, the pilot may apply pressure to have a deflection of the brake pedal of <NUM>% of the maximum deflection of the brake pedal. In step ii), the brake command may be between <NUM> and <NUM>% of the total brake command possible. It will be understood that the medium command level, is "medium" in the sense that it is higher than the aforementioned low command level, but not as high as the highest possible command level.

Preferably, the braking torque and driving torque are applied to the same wheel of the landing gear.

Preferably, a magnitude of braking torque provided increases as the command level within the sub-range increases. In other words, the magnitude of braking torque provided increases as the command level within the sub-range increases. For example, as there is more brake command from the brake command device (a pilot pressing harder on a brake pedal, for example), the more braking torque is applied.

The magnitude of braking torque may increase linearly as the command level within the sub-range increases.

Preferably, the method comprises the steps of step i) of appended claim <NUM> during a non-braking time period, then step ii) of appended claim <NUM> during a "transition" braking time period, and then step ii) of any of appended claims <NUM> to <NUM> during a "combination" braking time period.

In other words, the method involves at least three stages; a first non-braking stage where there is no change to the driving torque applied and no braking torque applied, a second stage where the driving torque is reduced but no braking torque is applied and a third stage where the driving torque is (further) reduced and braking toque is applied.

Preferably, the method concludes with the step of during a non-driving time period braking the aircraft by using braking torque provided by the landing gear brake system, and not providing a driving torque from the landing gear drive system. This would be a fourth stage if combined with the three stages of the previous paragraph.

Preferably, the "non-driving" sub-range represents command levels at a high command level from the brake command device. In other words, it occurs where there is a high brake command (a pilot pressing with high pressure on a brake pedal, for example). For example, the brake command may be above <NUM>% of the total brake command possible. For example, the pilot may apply pressure to have a deflection of the brake pedal of <NUM>% of the maximum deflection of the brake pedal. In this step, the brake command may be between <NUM>% and <NUM>% of the total brake command possible.

This "non-driving" sub-range may occur where the brake command is equivalent to more than <NUM> or <NUM> bars of brake pressure.

The taxiing of the aircraft may be in a forwards or a backwards direction.

The brake command device may be a brake pedal, or other cockpit control. The command level may be determined by the amount of deflection of or the amount of pressure/force applied to the brake pedal/control.

According to a second aspect of the invention there is also provided an aircraft controller for controlling an aircraft during taxiing, the aircraft controller comprising a brake command device input indicating a command level of a brake command device over a brake command range, a drive command device input indicating a command level of a drive command device, and a landing gear drive system command output providing a command for a landing gear drive system, wherein the controller is configured so that i) when the brake command device input indicates a command level in a first sub-range of the brake command range, the landing gear drive system command output provides a command for the landing gear drive system to provide a driving torque to taxi the aircraft, and ii) when the brake command device input indicates a command level in a second sub-range of the brake command range, the landing gear drive system command output provides a command for the landing gear drive system to provide a driving torque that is lower than that in i) yet still positive.

Preferably, the controller is configured so that the reduction command of the driving torque increases as the command level within the sub-range increases. In other words, the magnitude of driving torque provided decreases as the command level within the sub-range increases. For example, as there is more brake command from the brake command device (a pilot pressing harder on a brake pedal, for example), the less driving torque is applied.

The controller may be configured so that the reduction command of the driving torque increases linearly as the command level within the sub-range increases.

Preferably, the first sub-range of the brake command range represents command levels at a zero or very low command level from the brake command device. The first sub-range may correspond to a non-braking step. There may be either zero command level from the brake command device or a very low command level from the brake command device. In other words, this occurs where there is either no brake command or only a very low brake command (a pilot pressing very lightly or not at all on a brake pedal, for example). For example, the brake command may be up to <NUM>% of the total brake command possible. For example, the pilot may apply pressure to have a deflection of the brake pedal up to a <NUM>% of the maximum deflection of the brake pedal. The brake command may be up to between <NUM> and <NUM>% of the total brake command possible.

Preferably, the second sub-range of the brake command range represents command levels at a low command level from the brake command device. The second sub-range may correspond to a "transition" step. There may be command levels at a low command level from the brake command device. In other words, this occurs where there is a low brake command (a pilot pressing relatively lightly on a brake pedal, for example). For example, the brake command may be between <NUM>% and <NUM>% of the total brake command possible. For example, the pilot may apply pressure to have a deflection of the brake pedal of <NUM>% of the maximum deflection of the brake pedal. The brake command may be between <NUM> and <NUM>% of the total brake command possible.

Preferably, the controller comprises a landing gear brake control system and wherein the landing gear brake control system comprises a landing gear brake system command output providing a command for a landing gear brake system, the landing gear brake control system being configured so that i) when the brake command device input indicates a command level in the first sub-range of the brake command range, the landing gear brake system command output provides a command to the landing gear brake system to not provide a braking torque, and ii) when the brake command device input indicates a command level in the second sub-range of the brake command range, the landing gear brake system command output provides a command to the landing gear brake system to provide a braking torque.

More preferably, the landing gear brake control system is configured so that the command of the braking torque increases as the command level within the sub-range increases. In other words, the magnitude of braking torque provided increases as the command level within the sub-range increases. For example, as there is more brake command from the brake command device (a pilot pressing harder on a brake pedal, for example), the more braking torque is applied.

The landing gear brake control system may be configured so that the command of the magnitude of braking torque may increase linearly as the command level within the sub-range increases.

The second sub-range of the brake command range may represent command levels at a medium command level from the brake command device. The second sub-range may correspond to a "combination" step. There may be command levels at a medium command level from the brake command device. In other words, this occurs where there is a medium brake command (a pilot pressing with reasonable pressure on a brake pedal, for example). For example, the brake command may be between <NUM>% and <NUM>% of the total brake command possible. For example, the pilot may apply pressure to have a deflection of the brake pedal of <NUM>% of the maximum deflection of the brake pedal. The brake command may be between <NUM> and <NUM>% of the total brake command possible.

Preferably, the controller is configured so that when the brake command device input indicates a command level in a low sub-range of the brake command range, the landing gear drive system command output provides a command for the landing gear drive system to provide a reduced driving torque than that in i), and so that when the brake command device input indicates a command level in a medium sub-range of the brake command range, the landing gear drive system command output provides a command for the landing gear drive system to provide a reduced driving torque than that in i), and the landing gear brake system command output of the landing gear brake control system provides a command to the landing gear brake system to provide a braking torque.

In other words, the controller is configured to control at least three stages; a first non-braking stage where there is no change to the driving torque applied and no braking torque applied, a second stage where the driving torque is reduced but no braking torque is applied and a third stage where the driving torque is (further) reduced and braking toque is applied.

Preferably, the controller is configured so that when the brake command device input indicates a command level in a further sub-range of the brake command range the landing gear drive system command output provides a command for the landing gear drive system to not provide a driving torque to taxi the aircraft, and the landing gear brake system command output provides a command to the landing gear brake system to provide a braking torque. This would be a fourth stage if combined with the three stages of the previous paragraph.

Preferably, the further sub-range represents command levels at a high command level from the brake command device. The further sub-range may correspond to a "non-driving" step. There may be command levels at a high command level from the brake command device. In other words, it occurs where there is a high brake command (a pilot pressing with high pressure on a brake pedal, for example). For example, the brake command may be above <NUM>% of the total brake command possible. For example, the pilot may apply pressure to have a deflection of the brake pedal of <NUM>% of the maximum deflection of the brake pedal. In this step, the brake command may be between <NUM>% and <NUM>% of the total brake command possible.

According to a third aspect of the invention there is also provided a landing gear drive and brake system comprising the aircraft controller as described above.

According to a fourth aspect of the invention there is also provided a landing gear drive system comprising a motor for providing a motor torque, a drive gear in drive connection with the motor, for providing a driving torque to a landing gear wheel during taxiing, and the aircraft controller of the second aspect for controlling the level of motor torque provided by the motor.

Preferably, the desired driving torque is the level of driving torque desired if there is no brake effect to be applied.

The reduction factor is the level of reduction to be applied to take account of a brake effect to be applied.

More preferably, the brake effect may be only as a result of the reduction factor or may be a combination of the reduction factor and a braking torque applied to a landing gear wheel.

Even more preferably, the braking torque is applied to the same wheel of the landing gear as the driving torque.

Preferably, the reduction factor may be such that the level of motor torque is zero.

In an unclaimed example, there may be provided a method of driving a wheel of a landing gear of an aircraft during taxiing, the method including a control unit controlling the amount of driving torque supplied to the wheel while braking is applied to the wheel or another wheel of the same landing gear in response to a received braking demand, and the control unit progressively reducing the still positive driving torque supplied to the wheel in response to successive increases in the braking demand.

<FIG> shows a graph <NUM> illustrating a method of operating an aircraft according to a first embodiment of the invention.

The graph has an x axis <NUM> representing the deflection of a brake pedal in a cockpit of the aircraft being operated by the method. The graph has a y axis <NUM> representing the torque applied to the landing gear of the aircraft being operated.

The graph shows the e-taxi drive system torque (driving torque) being applied to the landing gear by line <NUM>. This line <NUM> is entirely above the x axis <NUM> to show that the driving torque is considered to be in a positive direction. The graph shows the brake system torque (braking/resistive torque) being applied to the landing gear by line <NUM>. This line <NUM> is entirely below the x axis <NUM> to show that the braking torque is considered to be in a negative direction. Finally, the graph also shows the total torque (a combination of the positive driving torque and negative braking torque) acting on the landing gear by dashed line <NUM>. This dashed line <NUM> extends both above and below the x axis <NUM>, as the overall torque acting on the landing gear is both positive and negative during different periods of the method.

The graph can be considered to be divided into a number of areas or sections.

A first "driving area" <NUM> is the mode (i.e. the method is operating in a "driving mode") being operated when there is zero or a very low brake pedal deflection. In this embodiment, the "driving mode" is in operation when the brake pedal deflection is between <NUM>% and <NUM>% of the total brake pedal deflection possible. In this "driving mode", the driving torque <NUM> provided is at a set level, as commanded by a cockpit command. This is, for example, a dial in the cockpit to indicate the amount of torque to be provided by the e-taxi drive system in the absence of any brake command. Here, this cockpit command is at the maximum e-taxi torque level of <NUM>,<NUM> per wheel (applied to wheels <NUM> and <NUM> of the landing gear).

No braking torque <NUM> is applied by the braking system in this mode, so the total torque <NUM> is the same as the driving torque <NUM>.

A second "transition area" <NUM> is the mode (i.e. the method is operating in a "transition mode") being operated when there is a low brake pedal deflection. In this embodiment, the "transition mode" is in operation when the brake pedal deflection is between <NUM>% and <NUM>% of the total brake pedal deflection possible. In this "transition mode", the driving torque <NUM> provided is reduced from the previous set level of <NUM>,<NUM> per wheel. It can be seen that the driving torque <NUM> reduces linearly as the brake pedal deflection <NUM> increases within the range of <NUM>% to <NUM>%. In other words, the reduction of driving torque between <NUM>% and <NUM>% brake pedal deflection is the same as from <NUM>% to <NUM>%, for example.

A third "combination area" <NUM> is the mode (i.e. the method is operating in a "combination mode") being operated when there is a medium brake pedal deflection. In this embodiment, the "combination mode" is in operation when the brake pedal deflection is between <NUM>% and <NUM>% of the total brake pedal deflection possible. In this "combination mode", the driving torque <NUM> provided is reduced from the previous set level of <NUM>,<NUM> per wheel. It can be seen that the driving torque <NUM> continues to reduce linearly as the brake pedal deflection <NUM> increases within the range of <NUM>% to <NUM>%. In other words, the reduction of driving torque between <NUM>% and <NUM>% brake pedal deflection is the same as from <NUM>% to <NUM>%, for example. In fact, as the driving torque <NUM> also reduces at the same linear rate in the "transition mode" <NUM>, the reduction is driving torque between <NUM>% and <NUM>% is the same as the reduction as between <NUM>% and <NUM>%. At <NUM>% brake pedal deflection the driving torque <NUM> has reduced to zero.

Braking torque <NUM> is also applied by the braking system in this mode. In particular, the braking torque applied (in the negative direction) increases linearly as the brake pedal deflection <NUM> increases within the range of <NUM>% to <NUM>%. In other words, the braking torque increase between <NUM>% and <NUM>% brake pedal deflection is the same as from <NUM>% to <NUM>%, for example.

The total torque <NUM> in this "combination area" is positive in a first region 23a of the area, where the driving torque <NUM> is larger in magnitude than the braking torque <NUM>. The total torque <NUM> in this "combination area" is negative in a second region 23b of the area, where the braking torque <NUM> is larger in magnitude than the driving torque <NUM>.

A fourth "non-driving area" <NUM> is the mode (i.e. the method is operating in a "non-driving mode") being operated when there is a high brake pedal deflection. In this embodiment, the "non-driving mode" is in operation when the brake pedal deflection is above <NUM>% of the total brake pedal deflection possible. This is equivalent to <NUM> bars or more of brake pressure. In this "non-driving mode", the driving torque <NUM> provided is zero.

Braking torque <NUM> is applied by the braking system in this mode. In particular, the braking torque applied (in the negative direction) increases as the brake pedal deflection <NUM> increases. This increase in braking torque is at the same linear rate as for the "combination mode" up to <NUM>% brake pedal deflection and then the linear rate increases, so a higher braking torque is applied per % of further brake deflection above <NUM>% brake deflection.

The braking torque <NUM> reaches a maximum (negative) level of <NUM>,<NUM> per wheel (applied to wheels <NUM>, <NUM>, <NUM> and <NUM> of the landing gear) at <NUM>% (nearly full) brake pedal deflection. The total torque <NUM> in this "non-driving area" is the same as the braking torque <NUM>, as there is no driving torque <NUM> applied by the driving system in this mode.

<FIG> shows a schematic diagram <NUM> of an aircraft controller <NUM>, and other control systems <NUM>, <NUM>, according to a second embodiment of the invention, the aircraft controller <NUM> being used to achieve the method of the first embodiment, in relation to a right hand landing gear of an aircraft.

The diagram <NUM> shows a right hand (RH) brake pedal and associated sensor <NUM>. The sensor <NUM> outputs (as <NUM>) an indication of the RH brake pedal deflection (or brake pedal torque) applied by the pilot in the cockpit. Of course, this indication is also an indication of the target brake pressure desired by the pilot (for example a <NUM>% deflection of the brake pedal may correspond to a <NUM> bar target brake pressure). This indication <NUM> is output to both the aircraft controller <NUM> (see later) and to a RH brake control system <NUM>.

The RH brake control system <NUM> calculates (and close loop command) the RH desired brake pressure, illustrated by box <NUM>. This is done by assessing the level of brake pedal deflection. This RH desired brake pressure is then output (as <NUM>) to the RH brake system <NUM>, which applies this brake pressure and achieves a resultant braking torque corresponding to line <NUM> in <FIG>. The brake pressure is applied to all four wheels of the landing gear (wheels <NUM> to <NUM>).

The diagram <NUM> also shows a drive control system <NUM>. This system <NUM> comprises a cockpit drive control <NUM> that the pilot controls to indicate a level of taxi torque required. This may be a simple on/off switch but here, it includes a number of different torque levels, corresponding to a different desired aircraft taxi speed. This torque command level of the control <NUM> is output to box <NUM>, which calculates the RH taxi torque required, based on the level of <NUM>. This RH taxi torque is output (as <NUM>) to the aircraft controller <NUM>. The system <NUM> also calculates the LH taxi torque required (likely to be the same or very similar to the RH taxi torque required), based on the level of <NUM>. This LH taxi torque is output (not shown) to the aircraft controller <NUM>, which is also associated with the LH landing gear, or another aircraft controller that is associated with the LH landing gear.

The aircraft controller <NUM> uses the indication of the RH brake pedal deflection <NUM> to estimate the expected RH brake torque assessing the level of brake pedal deflection and calculate (in box <NUM>) the appropriate reduction factor, if there is one, (as per <FIG>) to apply to the driving torque to be supplied to the RH drive system. This is output to box <NUM>. Box <NUM> then applies this reduction factor, if there is one, to the RH taxi torque <NUM> commanded from the cockpit drive control <NUM>. This gives an actual RH taxi torque to be applied by a motor of the drive system, and this is output (as <NUM>) from the aircraft controller <NUM> to the RH taxi drive system <NUM>, which applies this driving torque to the motor and achieves a resultant driving torque corresponding to line <NUM> in <FIG>. The brake pressure is applied to two of the four wheels of the landing gear (wheels <NUM> and <NUM>).

Box <NUM> illustrates the total torque applied to the RH landing gear (from <NUM> and <NUM>) and corresponds to line <NUM> in <FIG>.

Importantly, it can be seen that the brake control system <NUM> is not changed in any way by using the aircraft controller <NUM>. Instead, an output <NUM> of the indication of the RH brake pedal deflection is simply outputted to the aircraft controller <NUM>, as well as the brake control system <NUM>.

An aircraft controller may be defined as comprising the aircraft controller <NUM> plus any elements of the brake control system <NUM> and/or drive control system <NUM>.

In the second embodiment described above, the output of the indication of the RH brake pedal deflection <NUM> is output from the RH brake pedal into the aircraft controller <NUM>. Instead, this output (or a similar one also providing estimation of the brake torque) may be outputted from the brake control system <NUM> rather than directly from the brake pedal <NUM>.

The second embodiment described above is shown in relation to a right hand main landing gear. Of course, it equally relates to a left hand (LH) landing gear.

The driving torque and braking torque in the above examples are applied to the wheels <NUM> and <NUM> and wheels <NUM> to <NUM> of the landing gear, respectively. Of course, it is also possible to for the braking and driving torque to be applied to different wheels of the same landing gear. For example, the braking torque could be applied to wheels <NUM> and <NUM> of the landing gear and the braking torque could be applied to wheels <NUM> and <NUM> of the landing gear.

The above examples provide specific values for the maximum driving torque, maximum braking torque, percentage of brake pedal deflection etc. Of course, these values may be different in other embodiments of the invention. For example, the braking torque <NUM> may reach a maximum (negative) level at <NUM>% (full) brake pedal deflection.

In the above examples, a brake pedal is used to command a braking from the pilot. Of course, any other suitable brake command device, such as a lever, may be used.

Reference should be made to the claims for determining the true scope of the present invention. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claim 1:
A method of operating an aircraft during taxiing, the aircraft having:
a) a landing gear drive system (<NUM>) for providing driving torque (<NUM>) during taxiing,
b) a landing gear brake system (<NUM>) for providing braking torque (<NUM>) during taxiing, and
c) a brake command device (<NUM>) with a plurality of different command levels (<NUM>) over a brake command range,
the method comprising the steps of:
i) during a non-braking time period;
- taxiing the aircraft by using driving torque provided by the landing gear drive system, and
- not providing a braking torque from the landing gear brake system, the method characterised by
ii) during a braking time period;
- providing the brake command device at one or more command levels within a sub-range of the brake command range, and
- controlling the landing gear drive system, in response to the level of the brake command device, to reduce the driving torque provided from that in step i) to a lower yet still positive driving torque.