WO2000039775A2

WO2000039775A2 - Assistance system for avoiding terrain collision for an aircraft

Info

Publication number: WO2000039775A2
Application number: PCT/FR1999/003186
Authority: WO
Inventors: Bruno Aymeric
Original assignee: Thomson-Csf Sextant
Priority date: 1998-12-23
Filing date: 1999-12-17
Publication date: 2000-07-06
Also published as: WO2000039775A3; FR2787907A1; FR2787907B1; EP1057160A1

Abstract

The invention concerns steering and air navigation assistance. More particularly it concerns a system to provide an aircraft pilot with instant assessment of terrain collision risks, comprising means for computing a forecast trajectory of the aircraft from its current survey point, a ground database including data concerning terrain position and altitude, and means for determining a risk of collision between the aircraft and the terrain on the basis of the forecast trajectory and the data concerning the terrain in the proximity of said trajectory. The system comprises means for displaying simultaneously on a screen a plot of the forecast trajectory (TP) and a symbol of terrain collision risk (ST1, ST2, ST3) representing the nature of the risk incurred, the symbol of risk being located on the screen, with respect to the plot of the forecast trajectory, at a position corresponding to the real relative position with respect to the forecast trajectory, of an obstacle creating said risk.

Description

AID SYSTEM FOR AVOIDING AIRLINES COLLISIONS WITH THE GROUND

The invention relates to assistance in piloting aircraft, and in particular assistance in avoiding collisions with the terrain.

This invention provides aircraft crews with the means of anticipating problems of conflict between the trajectory of the aircraft and the terrain, taking mainly into account the configuration of the terrain in the vicinity of the aircraft, but incidentally also the presence of '' other elements (other aircraft, adverse weather zones, etc.).

We currently have very complete field databases on board aircraft; there are also means for precise positioning of the aircraft at all times (GPS receivers, etc.); and we finally have means of processing these two sources of information to put them in relation to each other and determine the risks of conflicts.

Conventionally, to perform functions to help avoid collisions, terrain databases are divided into cells whose uniform altitude is the altitude of the highest terrain point in the cell. The cells are not all the same size: the lower the plane, the smaller the cells; if there is an aerodrome, the cells are smaller than if there is none. The size of the cells typically varies from 15 minutes of arc (region always overflown at high altitude) to 3 seconds of arc (near an airstrip).

Existing systems for assistance in the avoidance of collisions use the radio probe height, the instantaneous trajectory of the airplane, its position, and the terrain database. They provide an alarm when the separation from the terrain becomes insufficient taking into account the trajectory of the aircraft. The alert is given for example 60 seconds before the theoretical collision. The system does not give an alert any longer in advance so as not to disturb the crew, while the obstacle may be located in a place that the pilot has reasons to avoid anyway. Other systems present on a screen the configuration of the terrain relief as described in the database; the terrain can be represented in plan with cells colored differently according to their altitude, either compared to a reference level of the ground, or compared to the current altitude level of the airplane (for example coloring in red of cells whose difference in altitude with respect to the aircraft is too small), or again with respect to the instantaneous plane of descent of the aircraft (for example, coloring in red of cells whose difference in altitude with respect to the aircraft, when the plane will pass over this cell, is greater than that of the plane). The terrain can also be represented in lateral elevation, in the form of an altitude profile of the successive cells located on the path of the aircraft. Finally, the terrain can be represented in three dimensions; the image presented is then the one that a pilot would see through the windshield or the one that an observer would see following the plane while staying above and behind him. Each of these field representations can be faulted depending on the pilot's area of interest:

- if the pilot must undertake a U-turn and descend, a representation of the terrain from above (regardless of the cutting angle of the terrain) will not allow the terrain to be represented in an interesting way for the pilot;

- if the pilot wants to assess his lateral navigation margin in relation to the terrain, a lateral section or side view will not give any instruction.

To avoid these drawbacks, the invention proposes an aircraft piloting assistance system, comprising means for calculating a predicted trajectory of the aircraft from its current location point, a terrain database comprising information position and altitude of the terrain, and means for determining that there is a high risk of collision between the aircraft and the ground as a function of the predicted trajectory and of the terrain data surrounding this trajectory, characterized in that the system comprises means for simultaneously displaying on a screen a plot of the predicted trajectory and a collision risk symbol evoking the nature of the risk incurred, the risk symbol being located on the screen, relative to the plot of predicted trajectory, to a position that corresponds to the actual relative position, relative to the predicted path, of a soil creating this risk.

The display of this symbol on or near the predicted trajectory path can be done in a plan view or in a side elevation, or in both. A three-dimensional representation is possible as well as it offers less interest.

The system preferably displays on the same screen not only the predicted trajectory of the aircraft, calculated from the current position, the speed data of the aircraft, and the engaged and armed modes of the automatic pilot, but also the trajectory theoretical of the aircraft (i.e. its flight plan). The risk of collision is also determined in relation to this theoretical trajectory.

The risk of collision with the ground symbol may have a variable shape, dimension, color and / or contour depending on the conditions which led to its display, but it is indeed a risk symbol and not a more or less schematic representation of the real configuration of the terrain.

Preferably, the display is interactive in the sense that the system comprises means for designating on the screen a displayed collision risk symbol, and means for displaying, in response to this designation, additional information on the risks of collision associated with this symbol.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows and which is given with reference to the appended drawings in which:

- Figure 1 shows a screen view associated with the system according to the invention, the view being a top view;

- Figure 2 shows a screen view showing a side elevation along the predicted path of the aircraft; - Figure 3 shows a screen view similar to Figure 1, on which additional information, related to a particular terrain symbol, is displayed;

- Figure 4 shows a front view explaining additional information related to the particular terrain symbol. FIG. 1 represents an example of a screen as it would appear according to the invention during a navigation planned with a predetermined flight plan PV, represented by a line broken in solid lines but at a time when the airplane s 'is removed from this theoretical flight plan and follows a predicted trajectory TP represented here by a straight line in dotted lines.

The airplane is supposed to fly here on automatic piloting, in heading maintenance mode; the predicted trajectory TP is therefore represented by a vertical straight line intersecting a circular sector graduated in heading, the point of intersection between the predicted trajectory and the graduated sector representing the heading imposed on the aircraft by the on-board computer.

An AV aircraft symbol in the center of the graduated sector represents the aircraft's current position on its predicted path. The graduated sector, the airplane symbol, and the predicted trajectory remain generally at a fixed position on the screen, but the graduated sector revolves around its center when the airplane rotates. The position of the aircraft and its predicted trajectory are the geographic reference with respect to which terrain symbols will be represented on this screen.

Other navigation indications may appear on the screen, such as the names of the devices used at this time to determine the position of the aircraft, the elapsed time of the flight, the "aypoints" (navigation reference points), etc.

Terrain relief symbols ST1, ST2, ST3, specific to the present invention, are represented at various points on the screen, but only if the on-board computer determines that they must be represented because of the high risks they represent. An absence of risk will lead to an absence of symbol representation, whatever the altitude of the terrain overflown by the aircraft.

The terrain symbols are located on the screen at a position which represents, here in polar coordinates with respect to the airplane symbol AV and to the predicted trajectory TP, the real geographical position of the terrain at risk. The angle formed on the screen between on the one hand the predicted trajectory and on the other hand the axis connecting the airplane symbol to the relief symbol, corresponds to the deposit (in top view) of the relief at risk relative to the at the time of posting. The distance between the airplane symbol and the relief symbol represents the estimated distance between the airplane and the relief at risk. The screen is preferably graduated not only with regard to the heading (first polar coordinate), but also with regard to the distances. For example, two distance circles CD1 and CD2 are drawn concentrically to the sector graduated in heading, and are each assigned a predetermined distance value, preferably expressed in nautical miles. For example, the circle CD1 expresses a distance of 25 miles, and the circle CD2 a distance of 37.5 miles. These distances are displayed on these circles so that the pilot has an instant understanding of the geographical location of the reliefs at risk displayed by the on-board computer.

However, the graduation in distances is not necessarily constant during the various flight phases, the graduations can be separated by several tens of miles in cruise flight phase and only by a few miles or fractions of miles in approach phase aerodrome, the importance of the risks and the corrective measures to be taken being more critical during the approach phase.

In the example shown, a terrain symbol ST1 indicating a terrain at risk is displayed directly on the predicted trajectory of the aircraft, and two symbols ST2 and ST3 are displayed, one on the left, the other on the right of the trajectory. . The symbol ST3, in this example, is located between the predicted trajectory and the predetermined flight plan PV.

Just as the computer displays terrain symbols only when it determines that a risk of collision with the terrain exists (we will return to the risk existence decision factors later), it is also expected that it will display symbols for risk of collision with other aircraft. Such an aircraft collision risk symbol CA is also represented on the predicted trajectory. This of course presupposes that the aircraft is equipped with means for knowing the position of the aircraft which surround it, whether these means are radars or a radio system for direct communication between aircraft, by which the aircraft communicate their position automatically, in a standardized format directly usable by the on-board computer. The aircraft collision symbol CA is again represented on the screen at a position which represents, in polar coordinates, the relative position of the aircraft at risk with respect to the aircraft, and only if the risk is high. This representation of FIG. 1 is already in itself a precious and telling indication for the pilot. However, it can be supplemented with other information.

First of all, provision is preferably made for the computer to also display a representation in lateral elevation of the aircraft symbol, of its predicted trajectory, and of terrain terrain risk and aircraft collision risk symbols. This representation can be simultaneous with the first, for example in the form of a screen portion (or a screen juxtaposed to the first) reserved for the lateral elevation. For example, the side elevation view is placed just below the plan view. Or, it appears on the screen instead of the plan view, upon interrogation of the pilot.

FIG. 2 represents such an elevation representation in a vertical surface passing through the predicted trajectory (vertical plane for a linear trajectory). In this example, the predicted trajectory TP ′, which corresponds to the lateral elevation of the trajectory TP in FIG. 1, is a descent straight line, in the aerodrome approach phase. The airplane symbol is designated by AV. A vertical graduation in altitude is represented; a horizontal graduation in distance or flight time could also be represented; the AV airplane symbol is preferably fixed in vertical and horizontal position, the altitude graduation scrolling if the airplane changes altitude (the real altitude is given to the computer by the on-board instruments). The terrain symbols, displayed by the calculator in case of risk, scroll sideways from right to left as the risks get closer. Only the terrain risks which are, at a given time, located on the predicted trajectory of the aircraft (with a certain margin of course) are displayed in vertical elevation. In this example, the relief corresponding to the symbol ST1 in FIG. 1 is located on the path of the aircraft. It represents a risk because this relief is located at an altitude corresponding to the trajectory of the aircraft. It is represented, at the altitude it occupies in reality, by the symbol ST'1 in FIG. 2. If the airplane was not in the descent phase, this relief would not represent any risk: it would not would not be displayed in either Figure 2 or Figure 1.

We will enter further into the notion of risk assessment, but we can already notice about Figure 2 that the calculator displays a risk of aircraft collision (symbol CA 'corresponding to the symbol CA in FIG. 1) although the descent trajectory does not cut the altitude of the aircraft at risk. However, due to the presence of a conflict between the predicted trajectory and the terrain, the descent trajectory can be interrupted and the aircraft at risk can also change altitude, which implies that the risk is real.

The symbols ST2 and ST3 in Figure 1 are not shown in Figure 2 because they are sufficiently distant from the path laterally. It is preferable that the pilot does not see them overlapping on the side elevation where they would reduce the intelligibility of the representation. However, if the aircraft undertakes a change of course which brings it closer for example to the symbol ST3 by moving it away from the symbol ST1, the symbol ST3 may appear in FIG. 2 and the symbol ST1 may disappear.

Since the representation according to the invention is a representation at the same time complete but very simplified of the high risks of collision with the terrain, it is preferable that the pilot has the possibility of obtaining additional information on the risks indicated.

This information will preferably be obtained by moving a mobile cursor on the screen to a terrain symbol, and by "clicking" on this symbol, to launch a program for displaying additional information linked to this symbol.

For example, by clicking on the symbol ST3, located to the right of the aircraft, you can bring up a screen, almost identical to that of FIG. 1 but showing additional information which is a possible TS trajectory of the aircraft in the in case the pilot decides to join the PV flight plan. At the same time or separately, the screen can display on its lower part a new image, represented in FIG. 4, which is a representation in front view, graduated in altitude, with an airplane symbol (AV) and a representation terrain relief in cells of different altitude levels, with an indication that the terrain exceeds the maximum altitude that the aircraft can fly over, given its current altitude.

In the foregoing, it has been assumed that the airplane was flying on autopilot in heading maintenance mode. The invention also applies to other modes of automatic piloting as well as manual piloting. In manual piloting, the on-board computer will calculate the predicted trajectory from instantaneous speed and heading data for the aircraft. This trajectory will in principle be a straight line as in heading maintenance mode. In other autopilot modes, the predicted path shown on the screen will not necessarily be a straight line. For example, in a particular mode, the airplane must join a flight plan trajectory on which it is not currently. The computer will be "armed" in "navigation" mode to join the flight plan; when it has joined the flight plan trajectory, it will switch to "effective navigation" mode and will follow a trajectory which is the flight plan.

In this case, the predicted trajectory includes the catch-up trajectory (Autopilot in heading maintenance mode) and a portion of the flight plan which will be followed since the autopilot will enter navigation mode.

In the first part, the calculator develops a trajectory to reach the flight plan. It is this catch-up trajectory that will be displayed on the screen as a predicted trajectory, in relation to which the risks will be calculated and the terrain symbols displayed or not displayed. This trajectory has no reason to be a straight line; it can include broken segments or curves. In the second part, after the airplane has joined its flight plan or an alternative plan (in the case where it has left one first flight plan to join another), the predicted trajectory will be the flight plan, represented by example like the PV flight plan of figure 1, with an airplane symbol placed on this flight plan.

Similarly, in "armed" mode on "localizer", the autopilot prepares the aircraft to receive an electromagnetic beam from ground equipment called "localizer" or "LOC"; it establishes a predicted trajectory, straight or curved, towards an area where the signaling device called "localizer" transmits a radio location signal. The airplane symbols will be displayed by calculating the risks in relation to this trajectory. When the aircraft has reached the radio reception area, the autopilot will go into "effective localizer"mode; the system will calculate the predicted trajectory from the radio information received. The predicted trajectory will include, before intercepting the loc axis, a portion of this axis. It is in relation to this trajectory that risks will be calculated and displayed if they are high.

The system will also take into account the vertical modes of the autopilot. For example, one of these modes is conventionally "level change" in which an ascent (or descent) trajectory is taken until a set altitude is reached. In this case the system will predict the break in the vertical plane, when the set altitude is reached.

It will therefore be understood that the system uses to display the risk symbol not only the instantaneous predicted trajectory but also the calculated theoretical trajectory.

Generally, to determine if the risk is high enough to be displayed on the screen, we will try to find criteria. The criteria depend of course on the applications (civil, military, for small planes, for large planes, taking into account local laws or not, etc.).

As an example, one can imagine that one criterion is the possibility for the plane to turn around at any time. This is the reason for example of the display of the symbol ST2 in FIG. 1. If the airplane follows its trajectory it remains far from the terrain relief and the risk should not be displayed for this reason alone. But if we want to leave the plane the possibility to turn around at any time, and taking into account the fact that it cannot turn around from the right because of the presence of another relief at right, the computer will display the symbol ST2. By clicking on this symbol, the pilot could also have confirmation by the appearance on the screen of a U-turn trajectory which would pass over this symbol.

The computer can take into account other elements than terrain relief to arrive at the need to represent a symbol of high risk of terrain collision. For example, the presence of an unfavorable weather zone preventing a U-turn from the right can cause the appearance of a terrain symbol on the left, while the risk linked to the terrain would in other circumstances be low: the plane normally has the possibility to turn around on the right, but no longer has it because of the weather zone. The adverse weather symbol will appear on the right in addition to the terrain symbol on the left. This means that the system has increased the risk calculation margin due to the presence of this weather zone.

In general, the following information will be used when possible to develop the criteria for risk of collision with the terrain: - modes engaged on autopilot and associated setpoint values (for example heading maintenance mode engaged, with value of the set point);

- present and active flight plan in the FMS ("Flight Management System"); - existence of an alternative flight plan in the FMS

- aircraft position calculated by the FMS;

- altitude given by the on-board instruments

- instantaneous trajectory (instantaneous speeds along three axes) - state of engagement of the autopilot and the FMS

Other information may be taken into account: surrounding traffic situation; weather disturbances.

In practice, the computer will take into account four possible types of predicted trajectories: - instantaneous trajectory when the autopilot is not engaged;

- linear predicted trajectory when the autopilot is engaged but not directed by the FMS (flight outside the flight plan);

- active flight plan at the FMS in all cases; - optional, alternative flight plans.

Depending on the flight phase (navigation, approach) and the aircraft situation, other trajectories may occasionally be taken into account for the calculation and display of risks, for example:

- in the final approach phase, the terrain behind the airstrip may still pose a threat if the crew decides to go around. Thus, a trajectory initiated at decision height at the minimum rate of climb with one engine less (regulation requirement) may be considered to display a terrain symbol at a place where the separation margin would be reduced. - during the takeoff phase, a trajectory initiated at the end of the runway at minimum climb rate with one engine inoperative (regulatory requirement) may be considered to display a terrain symbol in a location where the separation margin would be reduced.

- when the flight plan of the FMS is no longer followed, and that for example the pilot performs the displays of the automatic pilot himself, the system considers the area between the trajectory of the flight plan and the predicted trajectory and identifies the separation between this area and the land.

These trajectories will be taken into account by the system with lateral and vertical margins. Thus, the system will consider that a trajectory is not defined as a wire, but as a tube of rectangular section. The section of this tube will take account of margins which will depend on:

- the accuracy of the location provided by the FMS,

- altitude error, - flight phase: for example, on final approach, the airplane is supposed to follow a fixed descent profile. In addition, it is natural for the aircraft to reduce its separation from the terrain. It is therefore not necessary to take a vertical margin. On the other hand, on an intermediate approach, the crew can receive an order from the air traffic control at any time to descend to a lower landing. A vertical margin will therefore be taken into account to generate symbols of lower priority but which can nevertheless warn the crew of the harmful consequence that a descent could have in certain places.

The present system can also take into account other "threats" to improve the diagnosis and adjust the lateral and / or vertical margins. For example, TCAS (Traffic Collision Avoidance System) anti-collision equipment can provide the present system with the position and instantaneous trajectory of certain airplanes sharing the airspace. This type of information will soon be able to be supplied more fully by the ADS-B (Automatic Dependent Surveillance Broadcast) radio collision avoidance system.

Thus, the present system will be able to carry out, along the above-mentioned trajectories, a verification of the separation margin of the airplane with the other planes, in priority at the places where the separation with the terrain is minimal. Similarly, the system will consider more margins important with the terrain where a minimum separation from another aircraft is planned.

The system can thus present the crew with a traffic symbol, associated with the terrain symbol, to indicate the predicted combination of two threats.

When the aircraft follows the predicted trajectory, it will not be necessary to constantly repeat all the protection calculations. On the other hand, certain calculation cycles could be more "loaded". The system will therefore manage the time available for the calculations by adjusting the time horizon considered for the predictions. Thus, basic, the system will only cover 5 minutes of flight, but depending on the resources available it will increase its coverage.

The flight plan protection will be performed on the entire flight plan, in the background. When the crew changes their flight plan, the system will cover the first five minutes immediately and the rest of the flight plan will be covered in the background.

On output, the system will send to the display systems:

- trajectory prediction if the FMS does not steer the autopilot: either manual or automatic. - the coordinates of the terrain symbols to be presented and the type of symbol.

- the identification of the trajectory relative to each symbol.

- the lateral and vertical margins predicted at these locations relative to the terrain. - the flight time to each symbol.

- the coordinates of traffic symbols to be presented and the identification of the corresponding aircraft.

- the coordinates of the weather symbols having been taken into account for the calculation of the margins. This information is not all displayed directly on the screen, but the pilot can obtain it on request.

The type of symbol displayed may depend on the different cases causing conflict detection. We could for example use the following classification: - a trajectory considered, to within the accuracy of localization, intercepts the ground: the most serious case.

- a lateral deviation or (exclusive) a vertical deviation (degree of deviation for each depending on the flight phase) would cause a conflict with the ground. - a lateral deviation and a vertical deviation (degree depending on the flight phase) would cause a conflict with the ground.

- a lateral deviation (significant deviation to take into account a "weather" conflict) would cause a conflict with the ground.

- a vertical deviation (significant deviation to take into account a "traffic" conflict) would cause a conflict with the ground.

Claims

1. Aircraft piloting assistance system, comprising means for calculating a predicted trajectory of the aircraft from its current location point, a terrain database comprising terrain position and altitude information , and means for determining a risk of collision between the aircraft and the ground as a function of the predicted trajectory and of terrain data surrounding this trajectory, characterized in that the system comprises means for simultaneously displaying on a screen a plot of the predicted trajectory (TP) and a collision risk symbol (ST1, ST2, ST3) evoking the nature of the risk incurred, the risk symbol being located on the screen, relative to the plot of the predicted trajectory, at a position which corresponds to the actual relative position, with respect to the predicted trajectory, of a ground obstacle generating this risk.

2. System according to claim 1, characterized in that it displays a symbol of another appearance if there is a risk of collision with another aircraft, the system then comprising means for receiving information on the position of other aircraft and means for determining a risk of collision with another aircraft.

3. System according to one of claims 1 and 2, characterized in that it displays a horizontal plan view of the predicted trajectory.

4. System according to one of claims 1 to 3, characterized in that it displays a side elevation view of the predicted trajectory.

5. System according to one of claims 1 to 3, characterized in that it simultaneously displays on the screen a plot of the theoretical flight plan of the aircraft and calculates the risks with respect to this flight plan.

6. System according to one of claims 1 to 5, characterized in that it comprises means for designating on the screen a collision risk symbol, and means for displaying, in response to this designation, additional information on the risk of collision associated with this symbol.