EP1695164A1

EP1695164A1 - Method for assisting low altitude navigation of an aircraft

Info

Publication number: EP1695164A1
Application number: EP04804792A
Authority: EP
Inventors: Guy Intellectual Property DEKER
Original assignee: Thales SA
Current assignee: Thales SA
Priority date: 2003-12-19
Filing date: 2004-12-13
Publication date: 2006-08-30
Also published as: FR2864269B1; WO2005069094A1; IL175942A0; US7584046B2; FR2864269A1; US20070150170A1

Abstract

The invention relates to a method for assisting low altitude navigation of an aircraft equipped with a computer capable of determining a flight plan ground path from passage points P of altitude alt(P) and from performances of the aircraft. The method comprises the following steps: for each point P, calculating a safe altitude, alt safe, to obtain a point Psafe; calculating a safety profile formed from segments joining the points Psafe; extracting the peaks S from points Psafe; determining the weight of the aircraft at these points S according to the distance between the aircraft and S and its consumption over this distance, the consumption being one of the performances; for each point S, determining the maximum gradient of climb MaxClimbFPA and the maximum gradient of descent MaxDescFPA according to the performances and the weight; defining two performance segments that present the gradients MaxClimbFPA and MaxDescFPA on either side of point S, and; calculate a performance profile, which is formed from performance segments and which enables a performance altitude, alt perf (P), to be associated with each point P of the safety profile.

Description

METHOD FOR ASSISTING THE NAVIGATION AT LOW ALTITUDE OF AN AIRCRAFT

The invention relates to navigation at low altitude of an aircraft. Methods of assisting navigation at low altitude are already known for highly maneuverable aircraft such as fighter aircraft. But they are not suitable for aircraft with limited maneuverability performance such as cargo planes or airliners. An important object of the invention is therefore to propose a three-dimensional (3D) navigation aid method, secure, at low altitude for an aircraft having limited performance. To achieve this goal, the invention proposes a method for assisting navigation at low altitude of an aircraft equipped with a flight management computer capable of determining a ground flight plan trajectory of the aircraft from '' a sequence of straight and or curved segments joining ground crossing points P having an altitude alt (P), the ground trajectory taking into account the performance and limitations of the aircraft, mainly characterized in that it comprises the following steps consisting of for the flight management calculator: - for each point P on the ground trajectory, calculate a safety altitude, a sec, to obtain a point P _S ec such that a sec (P _sec ) = Max [alt (P + mrg lat D), alt (P + mrg lat G)] + mrg green, mrg lat D and G being respectively predetermined right and left lateral margins, mrg green being a predetermined vertical margin, - calculate a safety profile formed by safety segments joining the po ints P _S é _C , - extract vertex points S from the points P _S ec of the safety profile such that the K points located before S and after S have a safety altitude lower than that of S, K being a determined parameter, determining the weight of the aircraft at these points S as a function of the distance along the safety profile between the aircraft and this point S and of the consumption of the aircraft over this distance, the consumption being one of the performances and aircraft limitations, - for each point S, determine the maximum climb gradient MaxClimbFPA that the aircraft can support to reach S and the maximum descent slope MaxDescFPA that the aircraft can support for follow the ground trajectory as low as possible after crossing S, depending on the performance and limitations of the aircraft and weight, define two performance segments which have a first end in S, MaxClimbFPA and MaxDescFPA slopes on both sides from point S and a second end at the point of intersection with the terrain or with another performance segment from another point S, - calculate a performance profile formed by performance segments and which makes it possible to associate with each point P of the safety profile, a performance altitude, ait perf (P). According to a characteristic of the invention, a low-altitude flight profile is determined from the safety profile and the performance profile. This process makes it possible to quickly calculate a three-dimensional flight profile that is safe and optimized to follow the ground trajectory, in particular in an environment with significant relief; it thus makes it possible to minimize the time during which the pilot of the aircraft must pilot manually before the automatic pilot can regain control with security on the updated 3D profile. According to a characteristic of the invention, the determination of the flight profile consists more precisely in calculating for each point P of the ground trajectory, a low altitude flight altitude, a flight, to obtain a point Pvoi such as a flight (Pvoi) = Max [a sec (P), a perf (P)], the low-altitude flight profile being formed by segments joining the points P _VO ι. The flyable profile is thus always higher than the (or equal to) security profile and therefore does not require a posteriori verification of the altitudes of the profile compared to those of the terrain. The flight management computer having wind speed and direction, aircraft speed, terrain altitude, local temperature, the MaxClimbFPA and MaxDescFPA slopes are preferably weighted according to the wind speed and direction and / or aircraft speed, and / or terrain altitude and / or local temperature. The invention also relates to a flight management system comprising a central unit which communicates with an input / output interface, a program memory, a working memory, a data storage memory, by means of transfer circuits. data, the input-output interface being connected to a database of the terrain to be overflown, characterized in that the program memory comprises a program for implementing the method as described.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, given by way of nonlimiting example and with reference to the appended drawings in which: FIG. 1 schematically represents an FMS flight management system , Figures 2a and 2b schematically represent a safety profile, seen in a section perpendicular to the ground path (Figure 2a), or in perspective (Figure 2b), Figure 3 illustrates the maximum climb slopes MaxClimbFPA and maximum descent MaxDescFPA , FIG. 4 schematically represents a ground trajectory, and safety, performance and flyable profiles at low altitude seen in section along the axis of the ground trajectory, FIGS. 5a, 5b, 5c, 5d schematically illustrate the calculation of a vertical transition around a summit or an obstacle S. We will consider below that the aircraft comprises a flight management computer FMS (acronym of the expression Anglo-Saxon "Flight Management System"). This FMS computer represented in FIG. 1, conventionally comprises a central unit 101 which communicates with an input-output interface 106, a program memory 102, a working memory 103, a data storage memory 104, by means of circuits 105 for transferring data between these various elements. The input-output interface is connected to various devices such as a man-machine interface 107, sensors 108, etc. A performance table, specific to the aircraft, and a ground flight plan trajectory are stored in the data memory. We recalls that a ground flight plan trajectory is established from a list of waypoints PP that the aircraft must fly over and is composed of straight and or curved segments joining these points as illustrated in FIG. 2b. The curves correspond to transitions calculated around the points PP taking into account the limitations of the aircraft. This ground trajectory is sampled according to a step p: a list of waypoints P, of ground altitude alt (P) is then obtained. In the performance table, we find the performance and limitations of the aircraft, for example the speed, slope of the aircraft, its maximum altitude, its stall speed, its consumption, its radius of turn, its roll, etc. The FMS computer is linked in particular to a database 109 of the terrain to be overflown, generally represented in the form of rectangular meshes. The method according to the invention is based on the determination of a low altitude flight profile by means of the FMS computer. It includes the following stages which consist in: a) Calculating from the ground trajectory, right lateral margins "mrg lat D" and left "mrg lat G" according in particular to the performance and limitations of navigation of the aircraft and the error on the estimated position or EPU (acronym of the Anglo-Saxon expression "Estimated Position Uncertainty"). When the error on the estimated position varies and when this variation is stabilized over time, the lateral margins are updated as well as the calculation which follows. These lateral margins are possibly identical. b) For each point P of the ground trajectory, calculate the maximum terrain altitude between the two limits defined by the ground trajectory offset by the right lateral margin, and that of the same point offset by the left lateral margin. At this maximum altitude, a vertical margin, "green mrg" is added to obtain a safety altitude, "has dried" of a point P _SEC . We can also write: a sec (P _S ec) = Max [alt (P + mrg lat D), alt (P + mrg lat G)] + mrg green The vertical margin is determined by the pilot, possibly taking the terrain into account . By thus associating these safety altitudes with the points P of the ground trajectory, one obtains a list of points P _S é _C joined by segments which form a safety profile illustrated in FIGS. 2a and 2b. c) Extract the highest points S from the safety profile, shown in Figure 4 by eliminating the lower intermediate points. This means that a point S is such that the preceding and following K points, K> 0, are located at a lower altitude. More precisely, a vertex S is such that the difference between the average slopes of the segments on the K preceding points and the K following points is greater than a threshold slope. The parameter K and the threshold slope depend on the relief and / or the performance and limitations of the aircraft; they are also preferably determined as a function of the sampling step p. We have for example K = 5, threshold slope = 5 ° for p = 300m. The purpose of this extraction of the vertices S is to reduce the number of points to be processed and consequently the response time of the flight calculator which must be as short as possible. The number of points to be processed is for example reduced by a factor of 20 to 50. When successive points S are too close, that is to say spaced less than a minimum distance Dmin, they are stored in a memory. list and only the two points S of this list having the highest altitude are retained. For example, Dmin is equal to them times the turning radius of the aircraft. d) Then estimate the weight of the aircraft at these points S as a function in particular of the curvilinear distance along the safety profile between the aircraft and this point S, of the consumption of the aircraft over this distance if the latter was traversed flat, that is to say with a zero slope. This consumption depends on the altitude of point S, the estimated speed, the performance and limitations of the aircraft, the wind speed and direction. Determine from this estimated weight in S and the specific performance table of the aircraft, the maximum slopes before and after each point S, i.e. the maximum slopes that the aircraft can support to reach S and to follow the ground trajectory as low as possible after crossing S. The maximum slopes coming from the performance table depend on the weight of the aircraft, the altitude of the peaks, the temperature variation ΔISA (acronym of the expression Anglo-Saxon "International Standard Atmosphere") in relation to the standard temperature, the speed of the aircraft and possibly the external loads to the aircraft which may have an impact on the drag forces. These maximum slopes, depending on the altitude of the terrain to be flown over and defined taking into account the most critical flight conditions (engine out, etc.), are respectively designated MaxClimbFPA for the maximum uphill slope and MaxDescFPA for the slope maximum downhill. They are represented in FIG. 3. MaxClimbFPA is notably determined as a function of the available power of the aircraft and possibly assuming an engine failure. These maximum slopes are then weighted according to the wind speed and direction. In the presence of a tailwind component, the aircraft must climb earlier and the slope of the climb segment towards S will be reduced or anticipated; that of the descent segment will preferably be maintained. In the presence of a headwind component, the slope of the climb segment towards S will be steeper and the aircraft will reach the altitude of summit S earlier; that of the descent segment will be reduced or delayed over time. The wind speed components are for example from short-term weather predictions or estimated in real time and are stored in the FMS data memory. The altitude of a starting point S and the maximum weighted slopes define two performance segments which have a first end in S, weighted MaxClimbFPA and MaxDescFPA slopes on either side of point S and a second end at point d intersection with the relief or with another segment. The segments determined for all the points S form a performance profile, which makes it possible to associate with each point P of the ground trajectory, a performance altitude, "ait perf". As for a point on the ground trajectory, there are two performance altitudes from performance segments, one rising, the other descending, the highest altitude is used as illustrated in Figure 3, in region III. e) Determine a low-altitude flight profile illustrated in FIG. 4 by choosing, for each point P of the ground trajectory, a flight altitude "has flight" equal to the highest altitude between that of the safety profile and that of the performance profile. We denote by P _vo ι, the point obtained. We can also write: ait vol (P _v oi) = Max [a sec (P), a perf (P)] The segments joining all the points P _VO ι form a flyable profile, which at each point P of the ground trajectory associates a flight altitude, "has flight". In the example of FIG. 4, the flyable profile coincides with the security profile on region I, and with the performance profile on region II. A new segment is created joining a point of the safety profile to a point of the performance profile as illustrated in region III. The determination of this flyable profile can be optimized according to the following three criteria which are minimized depending on the context: - average height between the flyable profile and the altitude of the terrain, - lateral margins, - response time of the calculation of the flyable profile by the flight computer. In the event of degraded operation of the device following for example a breakdown or a voluntary interruption of the function, the last criterion is preferred. Other optimizations can intervene. The ground trajectory is formed of segments and / or curves joining points P to be overflown. These points are generally distant by a constant step p shown in FIG. 2b. For example, we have p = 100m. This constant step sampling is costly in computation time for calculations based on this trajectory. A first solution consists in taking a larger sampling step p. Another solution consists in using a sampling step p varying as a function of the slope of the terrain; the points of the ground trajectory are filtered according to the slope between these points. The lower the slope, the greater the step p and, conversely, the more the slope varies, as is the case in mountainous terrain, the smaller the step p. The step, however, has a lower limit pι _nf and an upper limit p _su • We have for example p ^ _f equal to half a mesh width of the terrain database, ie approximately 0.15 / 2 N (nautical miles) and p _sup equal to about 1km. These solutions make it possible to reduce the number of points to be treated, by several specific filters. Often, as shown in FIG. 5a, taking into account the vertical safety margins of a conventional flight plan trajectory notably comprising a point P to be overflown passing through P ', the aircraft can fly over this point P by following a theoretical curve called theoretical vertical transition TV flown at constant load factor, and which passes under the planned flight path, that is to say under P ', at a distance ΔH. The theoretical vertical transition TV, calculated by the FMS, has the shape of a parabola which is tangent to the two segments joining P '. However, when the flight path is that of the low-altitude flight profile calculated as closely as possible, it is dangerous for the aircraft to follow this theoretical vertical transition which would pass under a point S as illustrated in FIG. 5b. A solution illustrated in FIG. 5c consists in artificially raising the flyable profile at S by a height ΔH to obtain S ': the expected vertical transition TV is thus also raised by ΔH with respect to TV. The flyable profile is then modified by adjusting the segments SegClimb, SegDesc coming from S, so that the new segments SegClimb ', SegDesc' coming from S 'are tangent to the expected transition TV as illustrated in FIG. 5c: we then obtain a new flyable profile. When the slopes (of one or more of the two new segments SegClimb ', SegDesc' are respectively greater than MaxClimbFPA and MaxDescFPA, (this or these) these new segments are replaced by segments SegClimb ", SegDesc" whose imposed slopes are respectively MaxClimbFPA and MaxDescFPA. The lower end of (this or these) segments SegClimb ", SegDesc" are then raised by a corresponding height ΔH 'as illustrated in FIG. 5d.

Claims

1. Method for assisting in navigation at low altitude of an aircraft equipped with a flight management computer capable of determining a ground trajectory of the flight plan of the aircraft from a series of straight segments and / or curves joining ground crossing points P having an altitude alt (P), the ground trajectory taking into account the performance and limitations of the aircraft, mainly characterized in that it comprises the following steps consisting in the computer for managing the flight to: - for each point P of the ground trajectory, calculate a safety altitude, has dried, to obtain a point P _Sé c such that has dried (Psec) = Max [alt (P + mrg lat D), alt ( P + mrg lat G)] + mrg green, mrg lat D and G being respectively predetermined right and left lateral margins, mrg green being a predetermined vertical margin, - calculate a safety profile formed by safety segments joining points P _S ec, - extract vertex points S among the points P _S é _C of the safety profile such that the K points located before S and after S have a safety altitude lower than that of S, K being a determined parameter, - determining the weight of the aircraft at these points S as a function of the distance along the safety profile between the aircraft and this point S and of the consumption of the aircraft over this distance, the consumption being one of the performances and limitations of the aircraft, - for each point S , determine the maximum climb gradient MaxClimbFPA that the aircraft can support to reach S and the maximum descent slope MaxDescFPA that can support the aircraft to follow the lowest ground trajectory after crossing S, depending on the performance and limitations of the aircraft and weight, define two performance segments which have a first S-shaped end, MaxClimbFPA and MaxDescFPA slopes on either side of point S and a second end at point of inters ection with the terrain or with another performance segment from another point S, - calculate a performance profile formed by the performance segments and which makes it possible to associate with each point P of the safety profile, a performance altitude, has perf (P).

2. A method of aid to navigation according to the preceding claim, characterized in that it further comprises the step of determining a flight profile at low altitude from the safety profile and the performance profile.

3. A method of aid to navigation according to the preceding claim, characterized in that the determination of the flight profile at low altitude consists in calculating for each point P of the ground trajectory, a flight altitude at low altitude, has flight, for get a point P _vo ι such that a flight (Pvoi) = Max [has dried (P), has perf (P)], the low-altitude flight profile being formed of segments joining the points P _VO ι •

4. A navigation aid method according to one of the preceding claims, characterized in that it consists in sampling the points P according to a step p, and in that K is determined as a function of p and or of a threshold slope and / or terrain and / or aircraft performance and limitations.

5. Aids to navigation method according to one of the preceding claims, characterized in that the flight management computer having an error in the estimated position, Mrg lat D and G are determined according to the performance and limitations of the aircraft and error on the estimated position.

6. Method of aid to navigation according to one of the preceding claims, characterized in that the flight management computer having the wind speed and direction, the speed of the aircraft, the altitude terrain, local temperature, MaxClimbFPA and MaxDescFPA slopes are weighted as a function of wind speed and direction and / or aircraft speed, and / or terrain altitude and / or local temperature.

7. A method of aid to navigation according to one of the preceding claims, characterized in that the aircraft being equipped with engines, the MaxClimbFPA slope is calculated by assuming an engine failure.

8. A method of aid to navigation according to one of the preceding claims, characterized in that the flight management computer being connected to a terrain database composed of meshes having a predetermined width L, and comprising information on the slope of the ground, it consists in sampling the points P according to a pitch p determined according to the slope of the ground and the width L of the meshes.

9. A navigation aid method according to one of claims 2 to 8, characterized in that a transition parabola being associated with the segments SegClimb, SegDesc of the flyable profile, coming from a vertex S, the top of the parabola being located at ΔH from S, it consists in: calculating a new vertex S 'located at ΔH above the vertex S, raising the transition parabola by ΔH, defining segments SegClimb', SegDesc 'from S' so that they are tangent to the raised transition dish and to obtain a new flyable profile.

10. Flight management computer of an aircraft comprising a central unit (101) which communicates with an input-output interface (106), a program memory (102), a working memory (103), a memory data storage (104), by means of data transfer circuits (105), the input-output interface (106) being connected to a database (109) of the terrain to be overflown, characterized in that the program memory comprises a program for implementing the method according to one of the preceding claims.