Abstract:
A terrain avoidance method and system for an aircraft includes a collision alarm device and an auto-pilot device including a first determination unit for determining a climbing order with optimal slope for the aircraft, a checking unit for checking whether a first altitude gain at the relief, by applying the optimal slope climbing order, is sufficient for clearing said relief, a finding unit for finding if at least one heading variation value exists, for which the corresponding altitude gain is sufficient to clear the relief, and a switching and calculating unit for applying to the aircraft, if the first altitude gain is sufficient, an optimal slope climbing order with an order to maintain the current heading and, if the first altitude gain is insufficient, a particular climbing order sufficient to clear the relief, with a heading order which corresponds to the selected heading variation value.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a terrain avoidance method and system for an aircraft. 
     BACKGROUND OF THE INVENTION 
     It is known that many aircraft, in particular civil transport aircraft, are equipped with a collision warning device making it possible to transmit a warning signal when there is a risk of collision of the aircraft with the terrain. With regard to the collision warning device, this can in particular be a TAWS (Terrain Awareness and Warning System) device, in particular of the EGPWS (Enhanced Ground Proximity Warning System) type or of the GCAS (Ground Collision Avoidance System) type. 
     When such a collision warning device transmits a warning signal, it is generally up to the pilot to take all action, in particular to pilot the aircraft manually in order to avoid a collision with the terrain. 
     The patent U.S. Pat. No. 4,924,401 proposes a solution having the purpose of automatically avoiding a collision of the aircraft with the terrain. This solution consists in defining a minimum altitude below which the aircraft must not descend and in automatically piloting the aircraft, by means of an automatic pilot, when that minimum altitude is passed through in descent, in such as way as to then automatically instruct the aircraft to climb and thus to prevent any collision with the terrain. 
     However, this known solution is particularly adapted to the case where the pilot is unconscious whilst the aircraft is in a dive. Because of this it has the disadvantage of acting very late in the aircraft&#39;s trajectory and the action on this trajectory of course is greater as it becomes later. Also, applied to a large passenger aircraft for example, this known solution causes an uncomfortable situation, or even a potential danger for the passengers. Moreover, the risk that the action of the trajectory will not protect the aircraft from a collision with the terrain is also high because of this late action. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to overcome these disadvantages. It relates to a particularly effective terrain avoidance method for an aircraft. 
     For this purpose, according to the invention, said method according to which there is used a collision warning device which monitors the flight of the aircraft with respect to the surrounding terrain and which is able to transmit a warning signal when there is a risk of a collision between the aircraft and a relief of the terrain by maintaining its current flight characteristics (speed, slope, etc), is noteworthy in that, when said collision warning device transmits a warning signal, automatically:
     A/ an optimal slope climb command for the aircraft is determined;   B/ it is checked if a first altitude gain (which is obtained at said relief by the aircraft, by applying said optimal slope climb command to it with a command to maintain the current heading), is sufficient to clear said relief; and   C/ according to this check:   a) if said first altitude gain is sufficient to clear said relief, said optimal slope climb command is applied to the aircraft with a command to maintain the current heading; and   b) if said first altitude gain is not sufficient to clear said relief, a search is carried out to see if there is at least one heading variation value for which a second altitude gain which is obtained at the relief by the aircraft (on applying to it an optimal slope climb command) is sufficient to clear said relief, and if it is so:
       α) one of said heading variation values making it possible to clear the relief is selected; and   β) a particular climb command which is sufficient to clear the relief is applied to the aircraft, with a heading command which corresponds to the heading variation value thus selected (and which therefore generates a heading variation of the aircraft).   
       

     The method according to the invention has the advantage of acting on the trajectory of the aircraft as soon as a risk of collision with the relief of the terrain has been detected, and this action is carried out automatically, that is to say without the intervention of the pilot. Thus, when a warning signal is transmitted, automatic action is taken in such a way as to improve the situation of the aircraft with respect to the terrain, by applying a climb command, generally an optimal slope climb command (with regard to the aircraft performance) as described below. 
     In order to do this, according to the invention:
         if such an action is sufficient to clear the relief, there is simply applied to the aircraft an optimal slope climb command without modifying its heading, which makes it possible to carry out a simplified avoidance maneuver; and   if the above simplified maneuver is not sufficient to clear the relief, which can happen in certain circumstances (very high relief, etc), the heading of the aircraft is modified in order to steer it in a direction in which the relief is not too high, and then there is (simply) applied to it a particular climb command which is sufficient to clear the relief in that direction.       

     Thus, due to the invention, there is in principle the ability to clear any relief which is situated in front of the aircraft. 
     In the context of the present invention:
         “slope” means both the actual slope and the attitude angle of the aircraft; and   “heading” means both the actual heading and the route of the aircraft.       

     Moreover, in the context of the present invention, the optimal slope climb command is determined taking account of an associated thrust command in order to be able to maximize the slope. As the maximal slope corresponding to the current thrust of the aircraft is not necessarily the highest, a thrust command is determined for which the maximal slope is the highest possible. 
     In a first simplified embodiment, said particular climb command, which is applied to the aircraft in step C.b.β, corresponds to an optimal slope climb command. 
     In a second embodiment, there is determined, as a particular climb command (at non-maximal slope) generating an altitude gain at the relief which corresponds to an altitude gain that is both necessary and sufficient to clear said relief. In this second embodiment, the method preferably begins by determining a heading (or route) value making it possible to minimize the route deviation of the aircraft, then there is determined a climb command (at non-maximal slope) making it possible to clear the relief whilst minimizing the change in slope (passenger comfort). This second embodiment therefore makes it possible to improve passenger comfort (because of a low slope and a low acceleration) without being prejudicial to the safety of the aircraft, since the altitude gain is sufficient to clear said relief. This second embodiment of course applies solely in the case where the altitude gain necessary to clear the relief is less than the altitude gain obtained on applying to the aircraft an optimal slope climb command, since, if this is not so, the latter climb command is applied. 
     Furthermore, the particular climb command sufficient to clear the relief is preferably calculated taking account of an altitude margin with respect to that relief (safety margin). 
     Furthermore, in step C.b.α, there is preferably selected (from among all of the heading variation values found) the smallest heading variation value, in absolute value, which makes it possible to divert the aircraft from its current heading as little as possible, that is to say from the initially predicted lateral flight path. 
     In the context of the present invention, it is of course possible to envisage other variants of the heading variation value selection used in step C.b.α. In particular:
         in a first variant, there is selected the heading variation value which corresponds to the lowest relief and which is situated in a predetermined heading variation range, defined on either side of the current heading of the aircraft;   in a second variant, there is selected the heading variation value for which the roll angle necessary for the corresponding heading change is, in absolute value, less than a predetermined value, for example less than 45°, in order not to degrade the climb performance of the aircraft too much (maximum possible slope).       

     In a particular embodiment, in step C.b.β, there is firstly applied said particular climb command, then there is applied said heading command generating a change of heading. This makes it possible to anticipate the climb command as early as possible and therefore to maximize the altitude gain obtained at the relief. 
     Furthermore, in a particular embodiment, when said collision warning device transmits a warning signal, the aerodynamic configuration of the aircraft is modified in such a way as to increase the altitude gain at the relief, and there is determined, in step A, an optimal slope climb command, taking account of the new aerodynamic configuration of the aircraft (resulting from this modification). This particular embodiment makes it possible to increase the altitude gain obtained at the relief. This embodiment can in particular be applied on an aircraft during an approach to an airport, for which the undercarriages are deployed, as are the slats, the flaps and/or the spoilers. In this case, the modification of the aerodynamic configuration sometimes consists simply in retracting these various items in order to obtain a better climb slope. However, in certain situations, it is more advantageous to leave certain items at least partially deployed (in particular the slats or flaps). In fact, the aerodynamic configuration of the aircraft is modified in such a way as to optimize the climb performance of the aircraft. The modification of the aerodynamic configuration can be carried out either automatically or by the pilot (by procedure). 
     Advantageously, when a heading command generating a heading variation is applied in step C.b.β, an identification signal is transmitted in the piloting position in order to inform a pilot of the application of this (heading variation) command. For this purpose, it is possible to indicate said heading variation command to the pilot, and also the climb command and the engagement of the terrain avoidance function. 
     Furthermore, when a risk of collision disappears, the aircraft is preferably returned into an operational flight envelope. 
     The present invention also relates to a terrain avoidance system for an aircraft. 
     According to the invention, said system of the type comprising:
         a collision warning device which monitors the flight of the aircraft with respect to the surrounding terrain and which is able to transmit a warning signal when there is a risk of collision between the aircraft and a relief of the terrain if it maintains its current flight characteristics; and   an automatic piloting device of the aircraft, is noteworthy in that said automatic piloting device comprises at least:   a first means of determining an optimal slope climb command for the aircraft;   a second means for checking if a first altitude gain (which is obtained by the aircraft at said relief on applying to it said optimal slope climb command whilst maintaining the current heading) is sufficient to clear said relief;   a third means to find out, when said first altitude gain is not sufficient to clear said relief, if there is at least one heading variation value for which a second altitude gain which is obtained at the relief by the aircraft (on applying to it an optimal slope climb command) is sufficient to clear said relief;   a fourth means for selecting, if necessary, one of said heading variation values making it possible to clear the relief; and   a fifth means for applying to the aircraft a climb command and a heading command, namely:
           if said first altitude gain is sufficient to clear said relief, said optimal slope climb command with a command to maintain the current heading;   if said altitude gain is not sufficient to clear said relief, a particular climb command which is sufficient to clear the relief, with a heading command which corresponds to the heading variation value selected by said fourth means (and which therefore generates a heading variation of the aircraft).   
               

     In a particular embodiment, said avoidance system also comprises:
         an indicating means automatically signaling the application of a heading command generating a heading variation, that is to say resulting in a lateral avoidance of the relief; and/or   a means of optimizing the aerodynamic configuration.       

     Moreover, said avoidance system advantageously furthermore comprises a means allowing the pilot to disengage it. In this case, said avoidance system can inform the pilot how to carry out the altitude and heading variations necessary for avoiding the relief (for example by means of an altitude and direction indicator which would indicate the attitude and the heading to assume). 
     Moreover, said automatic piloting device advantageously is part of an automatic pilot of the aircraft. 
     The appended drawings will give a good understanding of how the invention can be embodied. In these figures, identical references denote similar elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a system according to the invention. 
         FIGS. 2 to 4  are diagrammatic representations of various flight situations making it possible to give a good explanation of the essential features of a system according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The system  1  according to the invention and shown diagrammatically in  FIG. 1  is a terrain  2  avoidance system, for an aircraft A, in particular a large transport aircraft. 
     In order to do this, said system  1  is of the type comprising:
         a usual collision warning device  3  which monitors the flight of the aircraft A with respect to the surrounding terrain  2  and which is able to transmit a warning signal when there is a risk of collision between the aircraft A and a relief  4  of said terrain  2  if it maintains its current flight characteristics (speed, slope, etc); and   an automatic piloting device  5  of the aircraft A, which is connected by a connection  6  to said collision warning device  3 .       

     With regard to said collision warning device  3 , it can in particular be a TAWS (Terrain Awareness and Warning System) device, particularly of the EGPWS (Enhanced Ground Proximity Warning System) type or of the GCAS (Ground Collision Avoidance System) type. 
     According to the invention, said automatic piloting device  5  comprises at least the following means, which are in particular activated when said collision warning device  3  transmits a warning signal:
         a means  7  for determining, in the usual manner, an optimal slope climb command for the aircraft A, with respect to the actual performance of said aircraft A;   a means  8  which is connected by a connection  9  to said means  7 , for checking if a first altitude gain ΔH 0  (which is obtained at the relief  4  by the aircraft A when there is applied to it said optimal slope climb command determined by said means  7 , simultaneously with a command to maintain the current heading illustrated by a line  10  in  FIGS. 2 to 4 ) is sufficient to clear said relief  4  (for example a peak  4 A in the situation shown in  FIG. 2 );   a means  11  which is connected by a connection  12  to said means  8  for finding out, when said altitude gain ΔH 0  is not sufficient to clear said relief  4 , if there is at least one heading variation value ΔCi, i being an integer greater than or equal to 1, for which a corresponding altitude gain ΔHi (which is obtained at the relief  4  by the aircraft A when an optimal slope climb command is applied to it) is sufficient to clear said relief  4 ;   a means  13  which is connected by a connection  14  to said means  11 , for selecting in the way described below, from among the various heading variation values ΔCi found by said means  11 , one of these heading variation values. When the means  11  finds only one single possible heading variation value, said means  13  of course selects this single value;   a means  15  which is connected by a connection  16  to said means  13  for determining a particular climb command as defined below, as well as a heading command which makes it possible to change the heading of the aircraft A in accordance with the heading variation value selected by the means  13 ; and   a means  17 , for example a switching means, which is controlled by the means  8 , as represented by a connection  18  shown in dotted and dashed line in  FIG. 1 , and whose purpose is to transmit climb and heading commands according to this control.       

     More specifically, said means  17  is connected by connections  19  and  20  to said means  7  and  15  respectively and it transmits by the intermediary of a connection  21  a climb command and a heading command, which are such that they correspond:
         if said altitude gain ΔH 0  is sufficient to clear said relief  4 , to said optimal slope climb command determined by said means  7 , with a command to maintain the current heading of the aircraft A; and   if said altitude gain ΔH 0  is not sufficient to clear said relief  4 , to the commands determined by said means  15 , namely said particular climb command which is sufficient to clear the relief  4 , and said heading command which corresponds to the heading variation value selected by said means  13 .       

     In the context of the present invention, the optimal slope climb command is determined taking account of an associated thrust command in order to be able to maximize the slope. The maximal slope corresponding to the current thrust of the aircraft A not necessarily being the highest, the system  1  determines a thrust command for which the maximal slope is the highest possible. 
     Moreover, in the context of the present invention an altitude gain corresponds to the difference between the altitude obtained at the relief  4  and the current altitude of the aircraft A. 
     Moreover, an optimal slope climb command can be defined as follows: during a first time, the aircraft A is made to climb with a maximal angle of incidence, then it is made to climb at maximal slope. Preferably, the duration of this first time is chosen in such a way as to maximize the height that can be cleared at the relief  4 . 
     Said terrain avoidance system  1  of course also comprises means  22  (which can for example be integrated, at least partially, in the automatic piloting device  5 ) which apply in the usual manner to said aircraft A the climb command and the heading command received by the intermediary of said connection  21 . In order to do this, said means  22  of usual type comprise, for example, a means of calculating in order to determine control surface setting commands, on the basis of said climb and heading commands, and at least one means of actuating at least one control surface which receives this control surface setting command and moves said control surface in a corresponding way in order to apply said climb and heading commands to the aircraft A. 
     In a particular embodiment, said automatic piloting device  5  is part of a usual automatic pilot of the aircraft A. 
     Moreover, in a preferred embodiment, said terrain avoidance system  1  furthermore comprises a means of indication  23  which is, for example, connected by a connection  24  to said automatic piloting device  5  and whose purpose is to warn a pilot of the aircraft A when a heading variation command determined by the means  15  is applied to the latter. This information can for example be formed visually by means of a display screen  25  which is fitted in the cockpit of the aircraft A and/or in an audio way using a normal means which is not shown. 
     In the example shown in  FIG. 2 , the altitude gain ΔH 0  which is obtained at the relief  4 , which is in front of the aircraft A in the direction of its current heading (line  10 ), is sufficient to clear the corresponding peak  4 A of said relief  4 . In this example, the means  17  transmits to the means  22  the commands coming from said means  7 , namely an optimal slope climb command and a command to maintain the current heading of the aircraft A. In this case, the avoidance of the terrain  2  is therefore carried out in a simplified manner, simply by implementing a climb of the aircraft A without modifying its lateral flight path (maintaining the current heading). 
     On the other hand, in the examples of  FIGS. 3 and 4 , the altitude gain ΔH 0  obtained at the relief by application to the aircraft A of an optimal slope climb command whilst maintaining the heading (line  10 ) is not sufficient to clear the corresponding peak  4 B of said relief  4 . In this case, the means  17  transmits to the means  22  the climb command and the heading command which are determined by the means  15 . 
     As mentioned previously, the heading command which is generated by the means  15  has the purpose of modifying the heading of the aircraft A in accordance with the heading variation value selected by the means  13  from among the plurality of possible heading variation values ΔCi found by the means  11 . 
     In a preferred embodiment, said means  13  selects (from among all of the heading variation values ΔCi found) the smallest heading variation value in absolute value which makes it possible to divert the aircraft A as little as possible from its current heading (line  10 ), that is to say from the initially predicted lateral flight path. In the example of  FIG. 3 , the means  11  has found two heading variation values ΔC 1  and ΔC 2 . According to this preferred embodiment, the means  13  selects, in this example, the heading variation ΔC 1  which has the smallest absolute value. 
     Within the context of the present invention, it is of course possible to envisage other variants of selection of the heading variation value, implemented by said means  13 . In particular:
         in a first variant, said means  13  selects the heading variation value which corresponds to the lowest relief and which is situated within a predetermined heading variation range (ΔCL 1 +ΔCL 2  in  FIG. 3 ) which is defined on either side of the current heading (line  10 ) of the aircraft A and which is limited by segments  26  and  27 . In the example of  FIG. 3 , the part  4 C of the relief  4  which is in the direction  28  defined by the heading variation ΔC 2  is lower than the part  4 D of the relief  4  which is in the direction  29  defined by the heading variation ΔC 1  such that the means  13  selects the heading variation ΔC 2  in this first variant;   in a second variant, said means  13  selects the heading variation value for which the roll angle necessary for the corresponding change of heading is, in absolute value, less than a predetermined value, for example 45°, in order not to degrade the climb performance of the aircraft A too much.       

     Moreover, said means  15  also determines a particular climb command which is associated with said heading variation command determined in the previously described manner. 
     In a first simplified embodiment, said particular climb command determined by the means  15  corresponds simply to an optimal slope climb command. For a same optimal climb command, at a substantially equal distance from the relief  4 , the altitude gain ΔH 2  and ΔH 1  obtained for a heading variation is of course less than the altitude gain ΔH 0  obtained without heading variation, because of the energy used by the aircraft A in order to carry out the heading variation ( FIG. 3 ). 
     In a second embodiment, said means  15  determines, as a particular climb command, a climb command (at a non-maximal slope) which generates an altitude gain ΔHR, at the relief  4 , which corresponds to an altitude gain that is both necessary for clearing the corresponding part  4 D of the relief  4  and that is also sufficient taking account of the usual regulation safety margins and less than said altitude gain ΔH 1  relating to a maximal slope climb, as shown in  FIG. 4 . In this second embodiment, the first step is preferably to determine a heading (or route) value making it possible to minimize the route diversion of the aircraft A, and then a climb command (at non-maximal slope) is determined making it possible to clear said relief  4  whilst minimizing the change of slope (passenger comfort). 
     This second embodiment therefore makes it possible to improve passenger comfort (because of a low slope and of a low acceleration) without this however being prejudicial to the safety of the aircraft A, since the corresponding altitude gain ΔHR is sufficient to clear the relief  4  (part  4 D). This second embodiment of course applies solely in the case where the altitude gain necessary to clear the relief is less than the altitude gain ΔH 1  obtained on applying an optimal slope climb command to the aircraft A. 
     Moreover, in a particular embodiment, said automatic piloting device  5  (or said means  22 ) firstly applies said particular climb command to the aircraft A and then said heading command generating a change of heading. This makes it possible to anticipate the climb command as early as possible and therefore to maximize the altitude gain obtained at the relief  4 . 
     Moreover, in a particular embodiment, when said collision warning device  3  transmits a warning signal, the system  1  modifies the aerodynamic configuration of the aircraft A in such a way as to increase the altitude gain at the relief  4 , and the means  7  determines an optimal slope climb command, taking account of the new aerodynamic configuration of the aircraft A (resulting from this modification). This particular embodiment makes it possible to increase the altitude gain obtained at the relief  4 . This embodiment can in particular be applied to an aircraft during an approach to an airport, for which the undercarriages, the slats, the flaps and/or the spoilers of the aircraft are deployed. In this case, the modification of the aerodynamic configuration sometimes consists simply in retracting these various elements (undercarriages, slats, flaps, spoilers) in order to obtain a higher climb slope. However, in certain situations, it is more advantageous to leave certain elements at least partially deployed (in particular slats or flaps). In fact, the aerodynamic configuration of the aircraft A is modified in such a way as to optimize the climb performance of said aircraft A. The modification of the aerodynamic configuration can be carried out either automatically or by the pilot (by procedure). 
     The terrain avoidance system  1  according to the present invention acts on the flight path of the aircraft A, as soon as a risk of collision with the relief  4  of the terrain  2  has been detected, and this action is carried out automatically, that is to say without the intervention of the pilot. Thus, as soon as a warning signal is transmitted by the collision warning device  3 , said system  1  acts in such a way as to improve the situation of the aircraft A with respect to the terrain  2 , by applying to it a climb command, generally an optimal slope climb command (with respect to the performance of the aircraft A). 
     In order to do this, according to the invention:
         if such an action is sufficient to clear said relief  4 , the system  1  simply applies an optimal slope climb command to the aircraft A without modifying its heading, which makes it possible to carry out a simplified avoidance maneuver ( FIG. 2 ); and   if the above simplified maneuver is not sufficient to clear said relief  4 , which can happen in certain circumstances (relief  4  very high, etc), the system  1  modifies the heading of the aircraft A in order to steer it in a direction where said relief  4  is not too high, and it applies to it a particular climb command which is at least sufficient to clear the relief  4  in that direction ( FIGS. 3 and 4 ).       

     Consequently, the system  1  according to the invention in principle makes it possible for the aircraft A to clear any relief  4  which is situated in front of it. 
     It will be noted that, on emerging from a conflict (disappearance of a warning signal), said system  1  preferably returns the aircraft A into an operational flight envelope. 
     Moreover, said system  1  furthermore comprises a means (not shown) making it possible for a pilot to disengage it. In this case, said system  1  can inform the pilot how to carry out the altitude and heading variations necessary to avoid the relief  4  (for example by means of a normal altitude and direction indicator which would indicate the attitude and heading to assume).