Patent Grant
8457872
This application claims priority to foreign French patent application No. FR 09 00832, filed on Feb. 24, 2009, the disclosure of which is hereby incorporated by reference in its entirety.
The invention relates to the flight management of an aircraft and more particularly to compliance with time constraints and/or relative spacing constraints.
The growth in air traffic density is compelling an increase in arrival rates. This involves the instigation of time constraints and maximum reduction in inter-aircraft separations which then become very tricky to maintain when the speeds are low, as in the final approach to a landing runway, and if the wind context changes. The bottleneck for air traffic is essentially during the approach phase because of the frequent uniqueness of the runway in service and of its associated approach, and of the obligatory maintaining of a safety separation distance between aircraft in the final approach so as to reduce the risks of collision or stalling related to wake turbulence or to unforeseen manoeuvres such as go-arounds. Today, this separation is essentially managed through the speed which is maintained at least equal between two successive aircraft. The flow of aircraft on landing is thus maximized by maintaining this minimum distance.
It may happen, however, that an approach procedure necessitates a large turn (minimum)120° as in turnaround procedures or traditional manoeuvres with a tailwind section (“circle to land”). Except, if a relatively strong wind exists, a major problem can occur when two aeroplanes following one another at the same speed are temporarily brought closer together on account of the wind.
The invention is aimed at alleviating notably the problem cited above by proposing a method for managing the flight of a first aircraft A1 flying along a trajectory and being subject to a temporal constraint defined by a date determined with respect to a fixed point i.e. by a temporal separation with respect to a second aeroplane A2, the said first aircraft A1 flying according to a constant air speed Va1 with an initial wind Ve, the said method being characterized in that it comprises the following steps:
According to a variant of the method according to the invention, the trajectory (200) comprising an arrival segment (201) and a final segment (202) that are parallel, the modification of the trajectory (200) is by half the distance (Dsep) calculated on the arrival segment (201) and by half the distance (Dsep) calculated on the final segment (202).
According to a variant of the method according to the invention, the trajectory (300) comprising an arrival segment (301) and a final segment (302) forming an angle α, the modified trajectory comprises a lengthening segment (307) situated straight ahead of the final segment (303), a modified turn (305) linked to the lengthening segment (307) and capture segment (306) linking the trajectory of the aircraft to the modified turn (305).
According to another variant of the method according to the invention, the said point of the temporal constraint being a point, the temporal constraint being expressed in the form of a determined date at the said fixed point (503), the said first aircraft (A1) comprising a flight management system calculating a remaining flight time (Tremaining) so that the aircraft arrives at the given point by flying at the air speed (Va1) and with the initial wind (Ve), the method furthermore comprises a step of measuring a wind discrepancy (ΔVe) with the initial wind (Ve), and in that the calculation of the distance (ΔD) follows the following relation:
ΔD=ΔVe·[Tremaining−K],
K being a factor related to the turn time.
According to a variant of the method according to the invention, the modification of the trajectory (500) is by half the distance (ΔD) calculated on the arrival segment (501) and by half the distance (ΔD) calculated on the final segment (502).
According to a variant of the method according to the invention, the trajectory comprises a final segment and an arrival segment forming an angle α, the modification of the trajectory consisting of an extension (507) of length equal to half the distance (ΔD), of a new turn (505) and of a capture (506) of the new turn (505).
The method according to the invention permanently maintains the safety separation distance with respect to the preceding aeroplane and/or ensures compliance with the next downstream time constraint. This aim is attained by altering the horizontal trajectory of the aircraft and therefore by temporarily lengthening or reducing the said trajectory. The method according to the invention has the advantage of not modifying the speed of the aircraft whose variation is limited by a flight envelope, variation of the speed of an aircraft not being recommended in the approach so as not to destabilize it during the landing.
By not modifying the speed of the aircraft, the invention makes it possible to guarantee a secure landing with no risk of stalling or of go-around arising out of an uncontrolled speed. Through its maintaining of the advised approach and landing speed, the invention has furthermore the advantage of not increasing the landing distance and therefore of optimizing the runway occupancy time under the conditions of the day.
The invention makes it possible to take into account a variation in wind projected on the aeroplane which is a source of delay or advance with respect to a temporal constraint. This problem is solved through an adjustment of flight distance at unchanged speed. Indeed, in the approach, the speed variation is limited. By contrast in the state of the art, regulation is achieved by changing speed and generally while cruising.
The invention will be better understood and other advantages will become apparent on reading the detailed description given by way of nonlimiting example and with the aid of the figures among which:
At the moment when the second aircraft A2 is making a large turn (typically to align itself with the final approach), the wind becomes against it while during the moment of the turn, the first aircraft A1 which is following is still pushed by the wind Ve, so bringing it closer to the second aircraft A2. This period during which the aeroplanes get dangerously close to one another is related to the turn time which can be of the order of 60 seconds (time for a 180-degree turn at the mean rate of 3 degrees per second). Knowing that the spacing is generally 90 seconds, there will be at least 30 seconds during which the two aircraft will get closer to one another. If it is considered that the two aircraft have an identical air speed Va, the second aircraft A2 flies at a ground speed of Va−Ve and the first aircraft A1 at a ground speed Va+Ve.
In this example, a first step of the method according to the invention is the acquisition, by the first aircraft A1, of the position of the second aircraft A2 and the measurement of the distance separating them. This is performed by reception of the data from the second aircraft (whose identification can be established and confirmed by the controller or the pilot if possible) which is emitted by a communication system making it possible to disseminate the position thereof in broadcast mode (ADS-B OUT), by the first aircraft A1 equipped with a reception system making it possible to receive the information broadcast by surrounding aircraft (ADS function-B IN). The acquired data are, for example, the following: a message time (Time stamp) indicating the time of transmission of the data, the flight identifier (Flight ID), a route followed by the aircraft (Track), the current position of the aircraft (latitude and longitude), the ground speed and the wind speed measured by the aircraft.
On the basis of the data received from the second aircraft A2, the system according to the invention calculates the ground distance between the two aircraft taking account of the known geometry of the approach (the trajectory 200 on the ground being assumed to be common to the two aircraft). The distance which separates the two aircraft is therefore the difference between the distance separating the first aircraft A1 from the runway threshold 204 and the distance separating the second aircraft A2 from the runway threshold 204, distance calculated along the trajectory.
The following step of the method according to the invention consists in modifying the trajectory so as to maintain the separation. The ground speed of the second aircraft A2 is Va2−Ve while that of the first aircraft 1 is Va1+Ve.
According to a first variant of the method according to the invention, since generally the speeds of the aircraft in sequence are globally identical, the approximation is made that the two aircraft are flying at an identical speed Va. The ground speed relative discrepancy is therefore twice the wind speed Ve when closing in on one another. To avoid closing in on one another, it will be necessary to lengthen the trajectory of the trailing aeroplane by a conservative value equal to the difference in ground speed between the two aircraft, as traversed in the time remaining until the first aircraft A1 enters the turn. Since the aircraft are separated with a minimum of 90 seconds and since at the standard rate a turn of 180 degrees lasts 60 seconds (3 degrees per second), then during the first 60 seconds, the second aircraft A2 sees its ground speed decrease from Va2+Ve (when it has the wind in its tail) to Vat−Ve (when it is heading into the wind) while the first aircraft A1 remains at the ground speed Vai+Ve. For the next 30 seconds, the speed discrepancy is constant 2Ve. For the next 60 seconds, it is the ground speed of the first aircraft A1 which reduces to Va1−Ve.
The first aircraft A1 closes in on the second A2 by a distance D proportional to the effective wind and to the separation time between the two aircraft:
D=2×Tsep(hr)×Ve(kt)=Tsep(sec)×Ve(kt)/1800
Where Tsep(hr) is the separation time between the two aircraft expressed in hours and Tsep (sec) the separation time between the two aircraft expressed in seconds and Ve (kt) the wind expressed in knots.
According to a second, more accurate, variant of the method according to the invention, the theoretical calculation is used which shows that the variation in relative distance D between the two aircraft is the integral along the trajectory of the difference in the ground speeds Vs1, Vs2 between the two aircraft, i.e. VS1−Vs2=(Va1+Ve1)−(Va2+Ve2)Ve1−Ve2 with the assumption that the aircraft have the same air speed Va1=Va2=Ve. Cos α1−Ve. Cos α2 after projections of the wind vector onto the aircraft vectors, thereby giving:
with α1 the angle between the speed vector Va1 and the wind vector {right arrow over (V)}W with norm Ve, α2 the angle between the speed vector Va2 and the wind vector {right arrow over (V)}W and D the distance between the two aircraft in nautical miles (Nm) Ve (kt) the wind expressed in knots.
The angles Ang1 and Ang2 respectively of the aircraft A1 and A2 with respect to the separation section (aircraft instantaneous heading−heading of the separation section), which aircraft headings varying according to the standard rate ω of 3°/sec at moments staggered over time (from the start-of-turn time of the first aircraft—here arbitrarily 0 seconds—until the end-of-turn time of the second aircraft—here 180 seconds—and considering a spacing of the two aircraft of 90 seconds) according to the following table:
The angles Ang1 and Ang2 are used to describe the evolution over time of the aircraft headings referred to the separation heading, also called heading of the tailwind section. The so-called tailwind section is the reverse route to landing, performed for various historical reasons (to evaluate the wind, to reduce speed, to deploy the landing configuration, to check the landing conditions, etc.).
To avoid closing in on one another, it is therefore necessary to lengthen the separation section of the trajectory of the first aircraft by D/2.
For example, in the case of a wind on arrival of 30 kts and a separation time of 90 seconds, the trailing aircraft will close up by 1.5 Nm which will be compensated for by adding 0.75 Nm to the separation section of the trajectory of the trailing aircraft.
In another variant of the method according to the invention, the approximation consisting in considering the first speed V1 to be equal to the second speed V2 is dropped. Accordingly, the speed discrepancy ΔV=Vs1−Vs2=(Va1+Ve1)−(Va2+Ve2)=Va1−Va2+Vwind. (Cos α1−Cos α2) is integrated over the time remaining up to the runway for the calculation of the distance D.
The step of acquisition, by the first aircraft A1, of the position of the second aircraft A2 and of measuring the distance separating them is identical to the previous example. The calculation step is a generalization of the calculation of the previous example. The first aircraft A1 closes in on the second A2 by a distance D calculated as in the above example (the variation in relative distance related to the wind taking place only in the runway alignment turn which is substantially the same).
The modification of the trajectory of the first aircraft A1 then consists in performing a capture 306 of an alignment turn 305 of radius R prolonged by a segment 307 with a distance X meeting up with the final segment 303 as in the diagram of
According to a variant of the method according to the invention, adjusting a trajectory of an aircraft also makes it possible to comply with a time constraint imposed on the said aircraft. Adjusting the trajectory without modifying the speed when there is little speed margin for example, makes it possible to continue to satisfy the time constraint. The adjustment is done: either by effecting a trajectory extension before arriving at a point with obligatory overflight (for example a destination time constraint), or by modulating turn transitions for so-called fly-by transitions (transition without obligatory overflight of the turning point), or by combining the above two schemes if the trajectory adjustment is limited by the width of the aerial procedure or route with horizontal navigation precision requirement (such as RNP Required Navigation Performance).
At a given initial instant T0, the distance along the initial trajectory 400 between the aircraft and the point of the time constraint 404 equals D. It is calculated by integrating the variation of the ground speed over the time remaining up to the constraint:
with α the angle between the wind and the aircraft vector, Ve the effective wind component, Vs and Va the ground and air speeds of the aircraft A1 and Tdestination the time of arrival at the point of the time constraint.
During the turn, the wind component vanishes, thus leaving:
D=Va·[Tdestination−T0]+Ve·[Tstart turn−T0]+Ve·[Tdestination−Tend turn]=[Va+Ve]·ΔT+Ve[Tstart turn−Tend turn].
Where T0 is the initial instant at which the calculation starts, when the aircraft has not yet made its turn. Tdestination is in fact the time constraint (RTA for Required Time of Arrival) which moreover is not necessarily at destination but very close and in any event after the last turn. Tstart turn and Tend turn are the respective times at which the aircraft turn begins and finishes.
If a wind component Ve is added to this ground speed Vs, compliance with the time constraint will then necessitate either modifying the air speed (which may be problematic in the approach because of the reduced speed envelope), or modifying the distance.
The next step of the method according to the invention consists in calculating a modification of trajectory remaining as operational as possible and inducing a distance discrepancy ΔD. The distance discrepancy ΔD follows the following relation:
If the wind alters and becomes Ve+ΔVe, a trajectory lengthening or reduction ΔD will be required. The modification of the trajectory ΔD follows the following relation:
ΔD=[(Va+Ve+ΔVe)·Tremaining−(Ve+ΔVe)·60 sec]−[(Va+Ve)·Tremaining−Ve·60 sec]=ΔVe·[Tremaining−K],
With Tremaining being the time taken to perform the distance D and K being a turn time factor taking account of the time required to carry out the turn which is for example 60 seconds at the standard turn rate. Tremaining is the discrepancy between the time constraint RTA and the initial time T0. D is the distance traveled with the wind Ve. D+ΔD is the distance traveled with the wind Ve+ΔVe. ΔD is therefore the distance discrepancy required in order to adhere to the time constraint RTA at constant air speed Va if the wind alters by ΔVe.
If there is an increase in the tailwind component (or a decrease in the headwind component), the length of the arrival segment 401 and that of the final segment 404 are increased by half the distance discrepancy ΔD.
If there is a decrease in the tailwind component (or an increase in the headwind component), the length of the arrival segment 401 and that of the final segment 404 are decreased by half the distance discrepancy ΔD.
This is possible only if the aircraft is not yet in the last turn. If the aircraft is already in the last turn, the requirement of minimum separation between traffic on approach implies that it is impossible to overstep the axis and therefore it is not possible to modify the trajectory.
The step of calculating a trajectory modification inducing a distance discrepancy ΔD differs from the previous step and employs the calculation mentioned in the second example above (see
If there is an increase in the tailwind component (or a decrease in the headwind component), the length of the final segment t 503 is increased by a distance discrepancy ΔD/2.
If there is a decrease in the tailwind component (or an increase in the headwind component), the length of the final segment 503 is decreased by a distance discrepancy ΔD/2.
In the above two cases, the arrival segment of the new trajectory 505 is created so as to capture the new turn situated at the end of the lengthened final segment.
According to a variant of the invention, the step 71 of choosing a transition of the trajectory selects the closest transition not yet selected upstream of the constrained point. The effect of this variant is to modify the transitions of the turns furthest from the aircraft first. This strategy has the advantage of not reacting too early when a discrepancy with a time constraint is noted, it being possible to lessen this discrepancy as the flight proceeds.
According to another variant of the invention, compliance with the time constraint is ensured by choosing one of the transitions situated the whole way along the trajectory between the aircraft and the constrained point and, on the other hand, transitions situated in the last turns before the constrained point. The effect of this is to regulate the discrepancy with the time constraint the whole way along the flight.
According to another variant of the invention, compliance with the time constraint is ensured by using on the one hand a scheme for regulating the speed according to the known art and on the other hand the method according to the invention.
The method according to the invention is distributed around the Situation Awareness 880, Guidance 800 and Trajectory 820 functions. It uses as input the prediction elements 840 constructed on the basis of the flight plan 810, performance database 850 and navigation database 830, as well as the aircraft position and its state vector originating from the Location module 870.
The method according to the invention makes it possible to reconstruct and adapt a trajectory around the turn which makes it possible to lessen and maintain an appropriate time discrepancy with respect to a preceding aircraft (maintaining separation) or with respect to a transit time constraint to pass a downstream point (maintaining timetable), by taking account of the information, received by ADS-B “broadcast” data communication, regarding the position and speed of the preceding aircraft.
In the case of maintaining separation, the principle consists in acquiring the position of the preceding aircraft by ADS-B, comparing it in real time through a Situation Awareness module 880 with the current position of the aircraft 870 and if the distance is insufficient for the safety separation, the trajectory is recalculated 820 by lengthening (if the two aircraft are getting closer) or shortening (if the two aircraft are moving further apart) for example the current section (general case) so as to keep the separation constant. The trajectory modification, previously accepted by the pilot, is dispatched to the guidance 800 which will be slaved thereto. The flight plan is not modified for all that and the guidance is done automatically by the FMS (“managed” mode).
The inherent speed of the aircraft situated downstream will be obtained by ADS-B reception of the speed of the aircraft (aircraft data frame of the ADS-B message).
The constant-wind measurement may emanate from the ATIS wind information provided by the airport or, if the former exists, from the downstream aircraft received by ADS-B means, mixed with the real wind measured upstream.
The calculation of the new trajectory consists in making a manoeuvre of DIR TO inbound type (direct linkup with pre-alignment of route on the leg following the TO point) on the point occupied by the aircraft downstream, taking account of a separation route of the aircraft upstream.
The solution to the problem will be achieved as a function of the angle of the trailing aircraft, of its distance with respect to the downstream aircraft, of the inherent speed of the two aircraft. If moreover the downstream aircraft provides speed information by ADS-B, then the difference in speed between the two aircraft will be taken into account.
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