Patent Application
20090292483
This invention relates to a device and a method for determining a runway state, as well as to an aircraft landing and/or takeoff assistance system and method, and to aircraft equipped with such devices and systems.
During the landing and takeoff, and more generally the taxiing phases of an airplane, knowledge of the surface state of the runway is of major importance. Prediction of the braking performance of the airplane indeed depends on this knowledge. It thus is possible:
Now, braking performances of an airplane on a so-called contaminated runway are very difficult to predict because of the difficulty in knowing reliably and precisely the contribution of the runway state to the deceleration of the airplane, in particular in terms of adhesion and of projection and displacement drags in the case of a deep contaminant. The contaminants can be any element happening to be deposited on the “original” runway, as for example rubber deposited during previous landings, oil, rainwater forming a more or less uniform layer on the runway, snow, ice, etc.
Knowledge of such a contribution of the runway can seem beneficial for improving landing systems such as the one described, for example, in the document FR-2897593.
This knowledge also can prove important for increasing the takeoff security of airplanes, the latter having to estimate, for example, the runway point of no return no longer permitting a completely safe emergency braking on the remaining runway portion.
Initial solutions for estimating the runway state already have been set up, but measurements of the runway adhesion today are very difficult, ineffective, unreliable and hard to transpose from the context of the measurement means used to that of an airplane taxiing on the actual runway.
There is known in particular the measurement of adhesion via traction engines or “mu-meters,” for example towed vehicles or special cars, that provide results that are disparate, potentially inconsistent among themselves, non-representative for an airplane because of different scales of phenomena such as the stresses and performance of the tires, and which moreover necessitate a closing of the runway during the measurements.
In practice there also is recourse to visual and manual inspection of the runway by control which then provides a type and a depth of contaminant which are or are not compatible with the performance calculation means of the airplanes. This approach, however, provides only an indication highly dependent on the place where this inspection was conducted.
Also, there are known “Reported Braking Actions” which in fact are the experience of the pilot of the previous airplane concerning his braking performances with a division into four simple levels: good/medium/poor/nil (in practice indicated by the following English terms: “good”/“medium”/“poor”/“nil”), from which it is possible to manually inform the airplane on approach for landing. But this solution is subjective, depends on the airplane and takes into account contributions other than the braking of the wheels (the pilot being unable to identify the precise part of the various braking means of his airplane: aerodynamics, engine thrust or counter-thrust and braked wheels).
On the contrary, this invention relates to a solution for estimating a runway state that is more objective and representative of the behavior of airplanes.
In this sphere, analysis solutions applicable later on the ground already have been developed for estimating a posteriori the state of the runway at the time of an incident or an accident in service, or for validating trial flights in “real time.”
These solutions generally rely on measurements of the deceleration of the airplane during landing. Then on the ground, delayed treatments are performed in order to estimate the adhesion of the runway on the basis of this measured deceleration, subtracting therefrom in particular aerodynamic, engine and contaminant components or contributions deriving from models based on other measurements performed on the airplane or outside.
These treatments performed take into account the type of airplane involved, since the measurement of deceleration alone does not allow an easy utilization by another airplane.
Moreover, these treatments are long, manual and not compatible with an intensive operation of an airport where an estimation of the state of the runway is required in a brief period before the following airplane in turn executes a phase of taxiing on the runway, either for landing or for taking off.
Furthermore, there is known from the document US 2006/243857 a method and a device for estimating characteristics relating to a landing runway. A real-time treatment is carried out, during which various airplane or external parameters are acquired and recorded. From these recorded parameters, an estimation of the deceleration due solely to braking is performed on the basis in particular of the deceleration Ax of the airplane, the engine thrust Areverse thrust and the aerodynamic drags Adrag. A friction profile “μ” then is established in order to determine whether or not the airplane is at braking limit, and to let the pilot know accordingly.
These information items, however, simply cannot be used in a time period satisfactory for informing the airplanes in approach.
The invention thus seeks to overcome the disadvantages of the prior art by proposing in particular a concise runway state determination with an on-board treatment of the measurements performed in order to inform the following airplanes as quickly as possible.
For this purpose, the invention applies in particular to a device for determining a runway state, placed on board an aircraft, comprising measurement means capable of collecting at least one datum on deceleration of the aircraft during a phase of taxiing of the aircraft on the said runway, and comprising in particular:
in which the means for estimating a runway state information item comprises:
Correlatively, the invention also applies to a method for determining a runway state, performed on board an aircraft, comprising a step for measuring at least one datum on deceleration of the aircraft during a phase of taxiing of the aircraft on the said runway, and comprising in particular:
in which the said first step of estimating a runway state information item comprises:
The on-board treatments make possible an automatic estimation of the runway state in a relatively short period, even though the airplane may not have completed its taxiing phase. In this way, the following airplanes are informed in due time.
Furthermore, the on-board treatments and associated devices are simplified because they are implemented in the actual aircraft, the characteristics and parameters of which are easily accessible in (quasi-)real time.
It is understood here that a runway state information item is intended to describe this state as independently as possible from any consideration of the airplane having performed this measurement. To this end, the information item obtained is clearly more objective concerning the state of the runway and can be used by any other airplane having characteristics different from the first. By way of illustration, such an information item can take on the form of a level of adhesion of the runway, of an aquaplaning or equivalent information item, of an information item relating to contaminant drags or of a characterization of the runway state by identification of a type and of a depth of contaminant.
In this way, according to the invention, the information item turned over has been at least partially decorrelated from the characteristics of the airplane so as to best describe the runway state effectively for the following airplanes. As this description or estimation is effected on board the airplane, unlike the prior art, treatments on the ground are simplified and it thus is possible to inform the other airplanes directly.
Moreover, through use of “typical” adhesion profiles, concise characterizations of the runway state that can be used in a manner similar to the criteria generated by the pilots in the “Reported Braking Action” process can be obtained.
By thus providing that each of the reference profiles corresponds to a precise and concise characterization of the contaminant, in particular by its type and its depth, it becomes easy, by virtue of the arrangements of this invention, to provide this concise information item to the following airplanes in a brief period.
In practice, the correlation between the adhesion profile determined during taxiing of the airplane and one of these reference profiles makes it possible from then on to determine automatically a precise characterization of the runway state, in particular that of the profile having the best correlation with the estimated adhesion profile.
In one embodiment, the device comprises a means for determining a quasi-nil adhesion threshold speed, aquaplaning type, skidding, in the said estimated adhesion profile, the said comparison means comprising a means for calculating a normed difference between the said profiles over a range of speeds excluding a neighborhood close to the said threshold speed. It is understood here that the threshold speed is the speed of occurrence of aquaplaning or the like. In particular, the comparison of profiles is performed over the entire range of measured speeds with the exception of the zone (neighborhood) around the threshold value. In this way, errors due to the discontinuity of the aquaplaning speed are avoided.
According to another characteristic of the invention, a step of determining limitations of the braking capabilities of the said aircraft is provided, so as to indicate whether the said estimated adhesion profile is a maximal or minimal profile. It then is envisaged to transmit this information to the broadcasting center and to other aircraft on approach in order to improve landing assistance.
In one embodiment, the said runway state information item is associated with at least one information item on position of the aircraft on the said runway. As it happens, not all the aircraft land on the same runway portions. In this way the determined runway state can be associated with this position on the runway. By putting such additional information together, it thus is possible to obtain a precise mapping of the landing runway.
In particular, the said first estimating means is equipped for carrying out estimations by partitioning the said runway into a plurality of runway portions according to position information items. By way of example, the runway can be divided into three portions. This division of the runway thus makes it possible to improve the correlation between the adhesion of the runway and the position of the airplane on the runway.
In one embodiment, the device also comprises a means for validating the said runway state information item estimated by a member of the crew of the said aircraft, in particular a pilot, prior to transmission to the said broadcasting center. With this action, the pilot confirms that the determined runway state corresponds to his knowledge of outside conditions. In this way the efficacy of the device and of the associated method is enhanced. This validation also can back up the pilots in their subjective experience.
According to one particular characteristic of the invention, the device comprises a means for estimating the reliability of the measured data or estimations made prior to transmission, the said transmission of the said estimated runway state information item being undertaken if the said measured data or estimations made are reliable. This arrangement ensures the consistency of the automatic device and makes it possible to minimize the errors transmitted to the broadcasting center and to the other airplanes. By way of illustration, this reliability can be estimated by the signal-to-noise ratio of the measured data or by a sufficient level of correlation (with respect to a threshold value) between compared adhesion profiles.
In one embodiment, there is transmitted at least one information item from an information item on adhesion of the said runway, for example one indication from among four levels, an average value of adhesion of the runway or the said estimated adhesion profile according to the groundspeed, an indication of a risk of aquaplaning or of skidding, in particularly according to the zones of the runway, and an information item relating to contaminant drags, for example the presence of such drags and the severities thereof.
In one embodiment, the said at least one measured datum comprises the ground speed of the said aircraft and the deceleration of the said aircraft, and the device comprises a second means for estimating an adhesion profile according to the speed of the said aircraft, with the aid of the said at least one measured datum, the said second estimating means comprising:
It was able to be determined during tests that the contaminant on the runway also made a contribution during taxiing of the aircraft, in particular during a braking. Thus it is provided that the second means for estimating the adhesion profile furthermore comprises a means for modeling contaminant contributions (projection, compression and/or displacement of the contaminant) due to the presence of a contaminant on the said runway, and is equipped for determining the said adhesion profile according to the said modeling of contaminant contributions. In particular, any useful information on a possible contaminant of the runway and allowing this modeling can be obtained during the approach phase of the aircraft prior to landing through communication with the airport as mentioned above. The estimations made then are more precise.
In general, a variant to the use of the contaminant contribution in the estimation of the adhesion profile consists in that the said runway state adhesion profiles, the reference ones, include a contribution relating to a contaminant drag induced by a contaminant corresponding to each of the runway states, respectively. Such contaminant drags depend on the airplane in question. The calculations to be carried out in the aircraft thus are limited. Moreover, higher-quality results are obtained because the runway state adhesion profiles are specific to a known type of contaminant, so that the associated contaminant contribution is calculated and introduced in precise manner into the profiles.
In one embodiment seeking to reduce the noise inherent in the measuring devices, there is provided a means for filtering the said measured data capable of smoothing out the said data over a predetermined time period, for example by averaging them. This arrangement applies in particular to the inertial acceleration measurement systems.
According to another characteristic seeking, for its part, to implement a better modeling and therefore characterization of each portion of the runway, there is provided a means for filtering the said measured data capable of determining various phases during the said taxiing, the said first estimation means then being equipped for acting independently on each of the said phases. Models specific to each of the taxiing phases then can be provided.
According to a particular characteristic of the invention, the said first step of estimating a runway state information item is activated starting from a threshold ground speed of the said aircraft. Thus the essential part of the taxiing/braking of the aircraft is of interest, the end of taxiing being less representative of the braking and therefore of the state of the runway. In particular a compromise is sought between the quantity of data acquired and treated in order to obtain an effective estimation of the runway state and an early treatment in order to transmit the result of this treatment to the aircraft on approach in due time. Thus, by way of example, it can be considered that a threshold speed of 20 knots constitutes a good compromise.
Correlatively, the method and the device according to the invention can comprise steps and means, respectively, relating to the characteristics set forth above.
The invention also applies to an aircraft comprising at least one device for determining a runway state such as set forth above.
Optionally, the aircraft can comprise means relating to the device characteristics set forth above.
The invention also relates to a piloting assistance system for aircraft, in particular for the landing thereof, comprising at least one device such as set forth above provided on at least one aircraft, and a broadcasting center capable of receiving a runway state information item determined by the said device and capable of transmitting this runway state information item to at least one other aircraft, in particular in approach phase. The utilization of this information item by the aircraft in approach phase can be varied, for example by display thereof for the pilot or by its use as input for a landing assistance system.
Likewise, the invention also applies to a piloting assistance system for aircraft, comprising a plurality of devices for determining a runway state such as set forth above and provided in a corresponding plurality of aircraft, and a broadcasting center, the said broadcasting center being capable:
so as to provide an enhanced runway state mapping to the said at least one other aircraft.
In this way there is obtained an improved mapping of the landing runway for the aircraft in approach phase. Of course, different policies for merging and retention of information items can be set up, such as the one for taking into account meteorological changes at the airport, or even age of the information items and replacement thereof with more recent corresponding information items (even position on the runway).
Correlatively, there is provided an aircraft landing assistance method, comprising steps relating to the means of the above system.
Other features and advantages of the invention also will become evident in the description below, illustrated with the attached drawings, in which:
On
Through a communication link 16 provided in particular for this purpose, airplane 10 communicates the runway state that it has determined to a central station 18 of the airport. The latter, after internal treatments if need be, communicates (20) a runway state to airplanes 22 in approach phase for landing or those ready for takeoff.
The latter in turn will officiate as airplane 10 at the end of their landing in order to enhance the central station 18 with additional information items on the runway state, in order to achieve in particular a still more complete mapping of the runway 12.
Indeed, the central station 18 acquires and records these runway state information items originating from the device of the airplane 10 and of the preceding airplanes, then merges them, the data from the other airplanes making it possible to reconstruct a temporal and spatial information item concerning the runway. Generally, this treatment and merging phase is conducted on the ground in order, for example, to be used in analyses of the FOQA (“Flight Operational Quality Assurance”) type. As a variant, such a phase can be conducted on board airplanes 22 that collect in de-coordinated manner the data from other airplanes (of the same company, for example) already having landed.
As will be seen later, the determination of a runway state according to an exemplary embodiment of the invention takes into account:
In this context, there is proposed a device for determining a runway state, placed on board an aircraft, comprising measurement means capable of collecting at least one datum on acceleration of the aircraft during a taxiing phase of the aircraft on the said runway. This device comprises in particular:
As will be seen in the explanations below, the estimation of the runway state information item can result from several operations performed on various data measured during taxiing, including the deceleration datum.
On
Device 14 comprises a plurality of measurement systems 401, 402, . . . , 40n, connected to an estimation calculation module 42.
In particular, the device comprises one or more ADIRS (for “Air Data Inertial Reference System”) inertial stations 401 providing module 42 with measurements of ground speed of the aircraft, position, acceleration and temperature; a flight management system FMS 402 (for “Flight Management System”); a GPS module 40n providing the position of airplane 10.
An Airport database 44 connected to calculation module 42 also is provided. This base 44 or airport navigation system OANS (for “On-board Airport Navigation System”) provides to module 42 basic airport data and GPS data for the runway. As a variant, the in-flight management system FMS 402 can provide such data.
In general, many data can be provided and used to improve the theoretical models, profiles and other algorithms mentioned below. By way of illustration, module 42 receives (from airport 44 or from other modules 40i of the airplane) the location of the center of gravity CG, the slope of runway 12, the outside temperature, wind data (force and direction), speeds (ground, true aerodynamic and calibrated), altitude data (pressure, . . . ), the mass of airplane 10, airport data, data on the runway used, in particular the GPS coordinates of the runway, GPS position data of the airplane, engine behavior parameters, information items on press-down of brake pedals, on state of movable surfaces (such as the hyper-airfoil devices, the elevator, the airbrakes, the ailerons), Boolean information items representative, for example, of the contact of the main gear on the runway and of the opening of the reverse doors.
It is noted that all or part of these data, mainly those deriving from dynamic data of airplane 10 or from outside conditions, for example, are updated according to time: speeds, engine thrust levels, wind, . . . . It then is provided to identify the measured data by hour and date in order to facilitate the comparison of certain measurements with the ground speed of airplane 10 at the same moment.
These measurements are carried out during the taxiing and braking phase of airplane 10 at landing, for example up to a threshold speed value on the order of 10 knots (or 18.52 km·h−1). In particular, measurements and recording of measured data can be started as soon as airplane 10 reaches a preset altitude above the airport. As a variant, the detection of the initial contact of airplane 10 on runway 12 can activate recording of the measured data.
Calculation and estimation module 42 then treats all or part of these data according to various steps described below, particularly in connection with
The result of the on-board treatment for estimation of the state of runway 12 performed by this calculation module 42 is provided in the form of one or more following information items:
A display 46 of these determined runway state information items is implemented in the cockpit of airplane 10. The pilot then validates (48) or does not validate these displayed data in relation to his judgment and to his visual data, that is, as it were, according to his automatic functions of “Reported Braking Action.” The runway state information items validated by the pilot then are transmitted (50) to the outside of airplane 10, to the control and management center of the airport, by standard means, for example radiofrequency.
As a variant, transmission (50) of runway state information items can be automatic without validation from the pilot.
A possible storage (52) of the calculated information items is implemented in airplane 10.
There now is described in reference to
In a step A0 not shown and performed during the approach of airplane 10 for landing, data on estimation of the state of runway 12 are acquired by the on-board system through communication with the airport. These data result in particular from the merging of several runway state information items provided by various airplanes already having landed. This merging makes it possible to provide the temporal and spatial evolution of the runway state for a manual use by the pilot or possibly automatic use by a landing assistance system, of the “Brake-To-Vacate” type (system allowing the pilot to designate and attain an access for runway 12).
For example, a textual display to the pilot of airplane 10, as follows, specifies for an airport and a given runway 32R, the estimations of the two preceding airplanes, here an A330 (commercial name) followed by an airplane Av1 mentioned previously, for three portions of runway 12:
As a variant, a graphic display on an airport map, for example, can be offered after spatial and temporal merging of the data, in particular by using a color code to reproduce the state of various portions of the runway.
Step A1 of acquiring data takes place in part prior to contact of airplane 10 on runway 12, in particular for acquiring fixed data, and in part after contact during the phase, strictly speaking, of taxiing and braking of airplane 10 on runway 12, for acquiring time-dependent dynamic data. This latter acquisition is carried out during the deceleration of the airplane up to a threshold ground speed of 10 knots, for example.
In step A2, the measured dynamic data are filtered and treated in order to eliminate a portion of the noise inherent in the measurements and in the instrumentation, to identify certain sequences (stabilized zones, aquaplaning for example) and to perform specific treatments according to the zones if need be (distinction of transitory conditions and stabilized zones, for example).
In particular, as illustrated by
It is observed here, as mentioned above, that the measured data are treated according to the ground speed of airplane 10 and not according to time.
As a variant, if different taxiing sequences are identified, the type of filtering can be dependent on the zones identified.
Step A3 consists of the actual calculation algorithm implemented by the module 42 for each sequence of the acceleration profile 60 and for each position on runway 12. This calculation algorithm itself is automatically activated starting from a certain threshold ground speed of airplane 10, for example 20 knots. As it happens, this speed is low enough to be able to benefit from a wide range of measurements for validating the data measured and estimations made, and high enough to be able to provide the results on the state of runway 12 as rapidly as possible for the following airplanes 22. In this connection, two airplanes 10 and 22 generally follow one another by a few minutes, on the order of 1 to 2 minutes, and the treatment provided can be performed by the current computers 42 in approximately one minute.
In detail, this step A3 comprises a first sub-step A3.1 of estimating a model representative of the braking contributions of airplane 10 and illustrated by
This estimation is carried out from general data (conditions of the moment: temperature, wind, runway, . . . ) and from data acquired from the airplane (speed, mass, aerodynamic configuration, engine behavior parameters, . . . ). The contributions of aerodynamic drag 70 of airplane 10 and the contributions of engine thrust 72 (as direct thrust or reversers) then are generated from a theoretical model (for example a simplified version of a model from the Flight Manual).
Such generating can be carried out, in particular, for each identified taxiing sequence, for example from contact of the main gear upon emergence of the spoilers, then from the emergence of the spoilers to contact of the nose, and finally from contact of the nose to the start of braking.
There also is generated the profile of vertical stress on the braked wheels of the airplane, according to standard techniques not described here.
In addition, the possible contribution of contaminant drag 38 also may be generated in similar manner (see
In sub-step A3.2, there then is estimated a braking profile of airplane 10 according to its speed. This profile, already shown in reference 34 of
The force of braking 80 of airplane 10 is obtained for each of the ground speeds of the latter by subtracting (in a ratio equal to the measured weight of the airplane) the aerodynamic 70 and engine thrust 72 contributions to the measured deceleration profile 62 of the airplane 10.
According to one contemplated embodiment, the contribution of the contaminant drags 38 can be taken into account in this step to refine the braking FBRK profile 80. As a variant, and as mentioned below in connection with sub-step A3.5, contaminant drags 38 can be taken into account later in the treatment process.
In order to establish a more precise braking profile 80, to the detriment of calculation resources and time, it is contemplated in a more precise embodiment to take into account the taxiing force (which generally is considered to be negligible and therefore not taken into account) as well as the contribution of the weight of airplane 10 according to the slope of runway 12.
In sub-step A.3.3, there is estimated the level of adhesion of runway 12 as illustrated by
It is noted here that by virtue of the hour and date identification of the measured data, it is easy to make the connection between each adhesion coefficient of the adhesion profile thus evaluated 90 (here without taking into account the contaminant drags 38) and the corresponding position of airplane 10 on runway 12. As a variant, there can be used techniques of the “Flight Path Reconstruction” or FPR type that make it possible to ensure that the measured data are consistent from a kinematical point of view, for example by making it possible to reduce errors in measurement through a constant or relative bias.
The evaluated adhesion coefficients can result from two different limitations, however, one known as adhesion limitation when the state of sliding or adhesion of the runway limits braking, and the other known as torque limitation when all the braking torque called for at the corresponding controls is released.
In the first case, the calculated coefficient μ is indeed the coefficient of maximal adhesion of the runway at the corresponding location for the corresponding airplane ground speed.
In the second case, if a torque called for by the brake had been greater (whether because of the pedal control, or the maximal brake capacity, or because of the deceleration controlled by the “autobrake”), the braking 80 profile might have been different. In this case, the calculated coefficient μ corresponds to a coefficient of minimal adhesion of the runway at the corresponding location, and not the coefficient of maximal adhesion.
In sub-step A3.4 it is thus provided to determine the state of limitation of braking for each of these calculated coefficients. Simple empirical and/or phenomenological criteria can be used as a basis.
For example, the position of the brake pedal and the pressure obtained can be compared. Knowing the characteristic relating to the theoretical pressure demand according to the pedal position, if the pressure obtained is lower, one then is limited by the anti-skidding (or “antiskid”) and therefore it is a matter of a limitation known as adhesion limitation.
In another example that can be devised, the deceleration called for (constant or otherwise, called for by the automatic braking system also known as “autobrake” or a “Brake-To-Vacate” type system) is compared. If the deceleration called for is considerable and it is not attained, then one has adhesion limitation.
Finally in still another example, the signals from the braking regulation (“antiskid”) system are picked up.
In the example of
This limitation description is retained with the adhesion profile.
In the following sub-step A3.5 illustrated by
According to the calculated coefficient of adhesion μ all during braking of the airplane, and the ground speeds associated with this datum, this evolution can be compared with known models (theoretical or empirical, regulation or otherwise) of runway states in order to identify an estimate of the current runway state.
In particular, models provided by European regulations can be relied upon, for example the following list: DRY (for dry runway), WET (for wet runway), WATER ¼″, WATER ½″, SLUSH ¼″ (for melted snow), SLUSH ½″, COMPACTED SNOW and ICY (for ice).
Thus for each of these models there is calculated the difference between the adhesion coefficient μ of reference 100 and the coefficient μ estimated from measurements 90 (here, the profile takes the contaminant drags into account) over the entire range of speeds. For this purpose, the standard L2 for distance between the two profiles can be used.
As a variant, this calculation may be made separately over the low- and high-speed zones, for example under Vp−Δ and over Vp+α, Vp being the theoretical aquaplaning speed of the airplane, the margin Δ making it possible to avoid overly large errors due to the discontinuity of the aquaplaning speed.
The reference model 100 having the smallest difference with the estimation 90, within the limit of a certain upper margin (the model having to be conservative, i.e. not giving an optimistic indication), is selected as describing the state of runway 12.
In the proposed example, the best correlation with the estimated adhesion coefficient μ is obtained with the reference model Water ¼″, taking into account projection/displacement drags (contaminant drags).
In a variant as introduced previously, instead of considering the forces of the contaminant drags in the estimation of the braking force, one can integrate them directly into the reference adhesion profile μ 100 and in this way have only one estimated profile μ 90.
According to one embodiment, some simple transformations can be used in order to better define the evolution or the model most closely approaching the estimation of adhesion profile μ 90. For example, a translation and a homotethy can be applied to take into account a possible slight difference in the data in relation to the reference profile.
In addition, it is possible to use standard identification techniques, in particular identification of the parameters of the model that best represent the measured data, for example by optimization or lesser squares, then validation through an appropriate criteria, for example by residual analysis.
According to one embodiment, in the case of inhomogeneous runways, that is, comprising zones contaminated by rubber, for example, and therefore slippery even for speeds below Vp, those zones can be excluded from the analysis, but not from the final indication on the runway state. Such contaminated zones can be detected easily from the adhesion profile 90, where the coefficient μ is surprisingly low in relation to the ground speed for which it was estimated, in particular when μ is below 0.1.
The process of calculation A3 is continued in sub-step A3.6 by the identification of a risk of aquaplaning. According to the estimated coefficient μ all during braking of the airplane and the ground speeds associated with this datum, it can be estimated whether or not there is aquaplaning (very low adhesion coefficient, lower than 0.1) and whether there is a risk of encountering it on other zones of the runway. As it happens, the phenomenon of aquaplaning is encountered with a very low p, on runways covered with a deep contaminant and for a ground speed in excess of approximately 60 m·s−1, in particular according to the type of aircraft.
Thus, the risk of aquaplaning is identified:
In sub-step A3.7, the quality and reliability of the estimations of the state of runway 12 made during the preceding sub-steps are evaluated.
Various criteria make it possible to judge the quality and reliability of the estimations provided.
In particular, the noise of the input measurements can be taken into account. In this connection, the signal/noise ratio of the deceleration measurements can be such that uncertainty about the actual measured deceleration value no longer is guaranteed and invalidates the runway state estimation.
Also, comparison with reference models 100 used during sub-step A3.5 makes it possible to test the quality of the data. The ability to correlate a runway state reference model 100 with the estimated profile 90 makes it possible to have confidence in the prediction.
Current conditions (meteo: intensity of crosswind or gusty wind, pilot orders such as joystick or rudder bars orders, failure situation) also are taken into account in the sphere of validity of the on-board model used during sub-step A3.1. For example, if the model does not take into account a joystick input from the pilot (for example in nosing up, which induces an increase in vertical stress on the braked wheels), one then can have an overly high evaluation of the true adhesion. These excursions outside the sphere of validity of the model must be taken into account and then penalize the quality of the results.
From these three criteria, a quality information item is generated, for example:
Quality=f(noise)×f(correlation)×f(conditions)
The quality information items can take the form of a note (on 3 for example) or of color (red, orange, green).
It is seen that, according to the quality level, the best estimation of runway state can be provided, if need be under the “conservative” criterion, or nothing can be provided if the estimation is considered too inaccurate, for example if one of the functions of the formula sends back 0 by reason of non-validity of the criterion. The quality estimation can apply to all or part of the measurements and estimations.
By way of illustration, other criteria can be taken into account, such as, for example, semi-empirical or phenomenological criteria. The latter, for example those already mentioned in sub-step A3.4 as well as an analysis of the antiskid signals, can make it possible to judge the quality of the estimations. For example, the presence of a torque limitation over all or part of the braking phase can penalize the result by minimizing the level of adhesion estimated over the zone having this limitation.
At the end of the period of taxiing on the runway (starting from a certain threshold ground speed, for example), the estimated data then are recorded automatically in step A4.
Then in step A5, possibly upon action by the pilot, the result of the estimations is displayed on the screen in the cockpit of airplane 10. Depending on the quality and reliability estimated in sub-step A3.7, the pilot can receive one or more of the following information items:
Upon action by the pilot validating all or part of the runway state information items that were offered to him, these are transmitted, in step A6, to the outside of the airplane (control center of the airport or airplanes on approach, for example) accompanied by the quality of the estimations found.
Transmission of the data can be carried out by radio or through a system such as ACARS (“Aircraft Communications Addressing and Reporting System” according to English terminology).
In the above example corresponding to airplane Av2 of
The information item transmitted then can be presented in the following manner:
The preceding examples are merely embodiments of the invention which is not limited thereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08 52777 | Apr 2008 | FR | national |
