The invention relates to the field of aircraft guidance.

It more particularly relates to an automatic method of guiding an aircraft such as a drone a position remote from an airport to landing of the aircraft on a runway.

STATE OF THE ART

Guidance systems existing drones possible to produce a self-guiding an unmanned along a predetermined path, for example corresponding to the path of an observation mission. To produce such a guide, the position of the aircraft is determined at regular intervals and compared with the path to be followed. This position is generally determined using a receiver of an absolute positioning satellite system, such as GPS or Galileo, called GNSS ( "Global Navigation Satellite System").

It may however happen that the aircraft's computer is unable to determine the current position of the aircraft, or because of a failure of a component of the aircraft, such as a GNSS receiver or because of an unavailability of the positioning system signal, for example in case of jamming thereof. Without knowing the position of the aircraft, the processor thereof is then unable to guide the aircraft to make it follow the predetermined path. The aircraft guidance system is then particularly unable to send it to its intended landing point such as an airport runway or a temporary airfield. The aircraft then risk crashing in an unknown position and be lost.

There is therefore a need of a guiding method for securely guiding an aircraft, independently, from a point of return to a remote airstrip and to land the aircraft thereon, despite the unavailability of satellite positioning, while reducing the workload of the drone operator, even without the intervention of the latter.

Document US 4,454,510 discloses an automatic assistance method for landing an aircraft on a runway from a given point, for which the distance and altitude of the aircraft are determined, until an end point. The method is configured to be connected to an altimeter and a distance measuring device configured to measure a gap azimuth of the aircraft with respect to the direction of magnetic north thus determined. It further comprises a phase of assistance for landing. It is therefore necessary in this process to geo-locate the aircraft and determine the altitude by establishing, in a preliminary step, the position of magnetic north and that of the runway, which is complex and requires calibration of the assistance system.

US 2009/055038 itself offers a similar method using as a reference axis for measuring azimuth gap the direction of the runway. Again, the process therefore requires the geolocation of the aircraft and determining its altitude and a calibration step of the assistance system.

Finally, document GB 2302318 discloses a guiding method for landing a UAV comprising determining the position of the aircraft at predetermined markings and the guidance of the aircraft up to a given point a point of hanging from altitude data calculated by an image analysis system and heading of the aircraft data.

PRESENTATION OF THE INVENTION

The present invention relates in a first aspect to an automatic assistance method for landing an aircraft on a runway from a point of return to an end point at which the aircraft between in contact with the runway, said method being implemented by a data processing device on board said aircraft and configured to be connected to:

- an altimeter configured to measure the altitude of the aircraft,

- a distance measuring device positioned at a ground station and configured to measure relative to a reference point an azimuth deviation of the aircraft relative to a reference direction connecting said return point and the position of the distance measuring,

said method being characterized in that it comprises:

- a phase of assistance to navigation back including:

-a guiding the aircraft, from azimuth difference measurements of the aircraft with respect to said reference direction transmitted by the distance measuring device, the point of return towards the position of the distance measuring device;

-a position determination of the aircraft at a predetermined capture point approximately aligned with the return point and the position of the distance measuring device;

-a guide the aircraft along a predetermined trajectory of the capture point to a predetermined point approximately aligned hooked with the axis of the runway from the altitude data provided by the altimeter and heading and speed data of the aircraft;

-a landing assistance phase comprising a guiding point of the hooked end point located on the runway.

For return point here is understood the point at which the aircraft is detected by the system of assistance for landing. Note that, in the invention, the return point is defined without its position (altitude, distance, etc.) is known and is used exclusively for defining the reference direction, which is then used to guide the aircraft Phase assistance to the return shipping.

The aircraft can thus be led to a capturing position known with the azimuth difference measurements provided by the distance measuring device can be guided from this position to the end point, without requiring the use of a plant performing navigation, incorporated into the aircraft.

Positioning the aircraft at the point of capture can be determined from distance data between the aircraft and a reference point on the ground aligned with the return point and the position of the distance measuring device.

Such data are used to position the aircraft along the reference axis extending between the points of Return- distance measuring device (AE) and thus know when the capture point B is reached.

Said distance data can be estimated from measurements of the propagation time of data packets between the ground station and the aircraft.

Said distance data can be estimated from measurements of the propagation time of data packets between the ground station and the aircraft, said ground station and aircraft comprising synchronized clocks.

The simple measurement of packet delay can be transmitted between the aircraft and the ground station for other needs and determines whether the capture point is reached, without making necessary the use of a system board or ground further, and thus minimizing the energy consumption by the aircraft.

Determining the positioning of the aircraft to the point of capturing may comprise the data rate estimation of said aircraft and determining a distance traveled by the aircraft from the return point from said speed data.

The data processing device being configured to be also connected to an optronic system comprising an image capture device installed in the aircraft and positioned along the axis of the aircraft and an image processing device , adapted to processing said image, speed of said aircraft data may be estimated by said optronic system ground running speed of measurement using images captured by said image capture device and elevation data provided by the altimeter.

The aircraft can determine its position on the axis point of return-distance measuring device (AE) independently with independent precision of the distance separating it from the distance measuring device and the ground station.

speed of said aircraft data may also be estimated by measuring a Doppler effect caused by movement of the aircraft on signals exchanged between the aircraft and the ground station.

The speed of the aircraft can thus be determined even under adverse weather conditions concealing the ground.

The data processing device being configured to be also connected to an image capture device installed in the aircraft, the position of the aircraft at the point of capture can be determined by detection of a bitter known position in at least one image captured by said image capturing device.

Such detection is used to determine the positioning of the aircraft to capture point B with a reduced uncertainty, the position of the detected landmark can be known very accurately.

The aircraft can be guided between the return point and the point of capture in a straight predetermined path toward the position of the distance measuring device.

Such path minimizes the distance traveled and therefore the power consumed by the aircraft to reach the capture point B.

The aircraft can be guided between the return point and the point of capture in a zigzag path or bearings.

Such a path allows to improve the accuracy of guidance of the aircraft, comparing the aircraft location data views by the distance measuring device and the corresponding values ​​as determined by the aircraft.

The data processing device being configured to be also connected to a camera on board the aircraft, the landing assistance phase may comprise estimating a position of the end point in an image of the airstrip captured by the camera and estimating a position of the aircraft as a function of said estimated position of the end point in the image and altitude data provided by the altimeter, and said guide of the aircraft from the point of the hooked end point is achieved by maintaining the aircraft aligned with the axis of the runway.

The guidance of the aircraft can thus be achieved throughout the landing with a lower uncertainty than if it were made from measurements of the distance measuring device. This increased precision helps guide aircraft safely between the point of hanging and the culmination and land it.

The data processing device being further configured to be connected to a transceiver on board said aircraft for receiving signals from at least three transceivers positioned on the ground, the landing assistance phase can understanding of the aircraft position data estimation from range data between embedded and said transceiver at least three ground transceivers.

The distance information between the aircraft and use of fixed points on the ground in a known position as the transceivers to the ground reduces the uncertainty of the position of the aircraft in order to accurately guide the aircraft up at endpoint.

According to a second aspect, the invention relates to a computer program product comprising code instructions for executing the method according to the first aspect when said program is executed by a processor.

According to a third aspect, the invention relates to a data processing device configured to implement the support method of the first aspect.

According to a fourth aspect, the invention concerns an automatic system to assist the landing of an aircraft on a runway from a point of return to an end point at which the aircraft comes into contact with the runway comprising:

- an altimeter configured to measure the altitude of the aircraft,

- a distance measuring device positioned at a ground station and configured to measure relative to a reference point an azimuth deviation of the aircraft relative to a reference direction connecting said return point and the position of the distance measuring,

-The data processing device according to the third aspect.

Said assist system according to the fourth aspect may further comprise an electro-optical system comprising an image capture device installed on the aircraft and configured to be connected to the data processing device.

Said assist system according to the fourth aspect may further comprise a camera and image processing device associated with, configured to be connected to the data processing device.

Said assistance system of the fourth aspect may further comprise:

- at least three transceivers positioned on the ground;

-a transceiver configured to receive signals emitted by said at least three transceivers positioned on the ground, on board said aircraft and configured to be connected to the data processing device.

Such computer program product, data processing device and system have the same advantages as those mentioned for the method of the first aspect.

PRESENTATION DES FIGURES

Other features and advantages will become apparent from reading the following description of an embodiment. This description will be given with reference to the accompanying drawings in which:

- Figure 1 schematically illustrates an example of guiding the landing of an aircraft on a runway from a point of return to an end point according to an implementation mode of the invention;

Figure 2 illustrates various components that may be included in a support system for landing an aircraft according to the invention;

- Figure 3 illustrates the two connections connecting the data processing device to a ground station as well as the distance measuring device included in the landing assistance system according to the invention;

4 shows a landing assistance system for an aircraft according to an embodiment of the invention;

- Figure 5 is a diagram diagrammatically showing an example of implementation of the automatic assistance method for landing an aircraft according to the invention;

6 illustrates the landing phase support according to the invention when the support system is equipped with a camera;

Figure 7 illustrates the positioning of a reticle in an image on the endpoint;

Figure 8 is diagram illustrating the calculation of corrected position data from measurements transmitted by the distance measuring device according to an implementation mode of the invention.

DETAILED DESCRIPTION

An embodiment of the invention relates to a method for automatic assistance landing of an aircraft 1 on a runway from a return point A to an end point D at which the aircraft comes into contact with the runway, as shown in Figure 1.

This method is implemented by a data processing device 2, a support landing system 3, as shown in Figure 2. The support system for landing 3 may also comprise an altimeter 4 on board of the aircraft and to which the data processing device can be connected.

Referring to Figure 1, the following points can also be defined:

- return point A: point at which the aircraft is detected by the landing assistance system 3. Note that, in the invention, this point is defined without its position (altitude, distance, etc. .) is known.

- capture point B: point at which the aircraft is entering a phase of alignment with the runway to land.

- hanging point C: the point aligned with the axis of the track which must pass the aircraft prior to landing.

The altimeter 4 may be a barometric altimeter or a laser altimeter. The pressure altimeter may be accurate to 10 meters and can be repositioned with the value of the atmospheric pressure QNH which is the barometric pressure corrected for instrumental errors, temperature and gravity and brought by means sea level (MSL or Mean Sea Level). In practice, the QNH pressure may be given with reference to the threshold of the runway, so that the altimeter shows the geographical altitude of the end point D when the aircraft is on the runway threshold in question . The laser altimeter can be accurate to 0.2 meters and be used when the altitude is less than 100 meters.

The aircraft 1 is also equipped, in known manner, an automatic driver configured to maintain flight the aircraft 1 according to a defined heading and altitude.

This process offers guided safely an aircraft such as a drone, independently, from a point away back to the airstrip, for example, that an airport or a more rudimentary trail, and landing the aircraft on the runway, despite unavailability or GNSS satellite positioning system, by first guiding the aircraft to a predetermined point, said capture point B, in a known position and relatively close to the track landing through a guidance of the aircraft in a desired direction, the deviation from said set being determined and transmitted by a ground system from a measurement of the aircraft azimuth data by relative to system ground.

For this, the data processing device 2 is capable of being loaded on the device and may include a computer and a communication interface. Such on-board computer may be a processor or microprocessor, type x-86 or RISC e.g., a controller or microcontroller, a DSP, an integrated circuit such as an ASIC or programmable such as a FPGA, a combination of such elements or any other combination of components to implement the calculation steps of the method described below. Such a communication interface may be any interface, analogue or digital, enabling the computer to exchange information with the other elements of the support system 3 such as 4 altimeter.

As shown in Figure 2, the computer 2 of the data processing device is connectable to a flight control system (VCS) 7. The flight control system 7 can be instructed to conduct the actual guidance of the aircraft in reference the direction to follow, to the capture point B, from guide data provided by the computer of the data processing apparatus, functions of the attitude data of the aircraft, such as heading, roll and pitch, determined by sensors in the SCV, and azimuth deviations of data provided by the ground system mentioned above. For this, the flight control system can transmit instructions to the aircraft control units such as electric actuators,

2 the data processing device can be connected to a ground station, usually placed near the airport or airstrip, via two connections as shown in Figure 3:

-a link 1 1, called "control / command" bidirectional radio and C2 in a band of the electromagnetic spectrum between 3 and 6 GHz, which allows the exchange of command and control messages between the ground station and the aircraft. The transmitted signals are modulated with a single carrier modulation and are transmitted / received with an omnidirectional antenna mounted on a mast head at the ground station;

- an assignment data link 12M and bidirectional radio in a band of the electromagnetic spectrum between 10 and 15 GHz, which allows the exchange of data flows generated by the various vehicle sensors. The transmitted signals are modulated using a multi-carrier modulation and are transmitted / received with a directional antenna such as a parabola, masthead mounted.

The support system for landing 3 also includes a distance measuring device

13. Such a distance measuring device is a system ground and connected to the directional antenna of the ground station used for mission link 12. The distance measuring device is configured to continuously measure the direction in which the aircraft is located, that is to say, the azimuth of the aircraft relative to a reference direction, such as north. The distance measuring device may also measure the elevation of the aircraft with respect to a reference plane, e.g., a plane tangential to the ground. The azimuth and elevation of the aircraft are measured with respect to a reference point, for example with respect to the position of the directional antenna mounted masthead. This reference point is called the position of the distance measuring device in the rest of the document and noted E. '

The method proposes to use these azimuth data determined by the distance measuring device for guiding the aircraft towards the position of the distance measuring device. More specifically, the direction to follow the aircraft is subject to a closed-loop control: the distance measuring device may measure and transmit to the aircraft a gap between these measured azimuth data and an azimuth corresponding to follow to the AE direction connecting the return point A and the position of the distance measuring E. from these azimuth difference data, the computer of the data processing device determines guide data and transmits them to the system flight control, then the aircraft flight control system can guide the latter in order to cancel the gap and guide the

This process step allows a relative guidance of the aircraft, without having to geo-locate by determining, in a preliminary step, the position of the return point A, the position of magnetic north or the position the airstrip as proposed in the prior art. The method of the invention is simpler and eliminates the prior calibration of the system. It suffices to detect the aircraft to start route guidance. In addition, use of the axis (EA) as the reference direction eliminates the use of a central vehicle navigation.

In one embodiment, the elevation of the aircraft is treated as its azimuth. The distance measuring device may also transmit to the aircraft a difference in elevation between the measured elevation of the aircraft and a reference elevation corresponding to the elevation in the direction AE measured when positioning the aircraft at the point of return A. the use of such a difference of elevation by the flight control system causes in this case a gradual decrease in the altitude of the aircraft at progressively the advance thereof towards the position of the distance measuring device.

In a second embodiment, only the azimuth difference measurements are used for guiding the aircraft, made at a constant altitude based on the measurements of the altimeter of the aircraft.

In a third embodiment, the measurements of azimuth and elevation are used for guiding but the altitude of the aircraft is maintained constant by varying over time the reference elevation used for measurements of difference of elevation.

In a final embodiment, a guide similar to the first embodiment is implemented until the aircraft has reached a minimum altitude, from which the guiding is carried out at constant altitude.

In the various implementation modes described below, the altitude data of the aircraft provided by the altimeter can be corrected if necessary to match the relative altitude of the aircraft with respect to a point reference, for example in relation to the altitude of the deviation measurement. This allows for example to overcome the altitude variations of the terrain over which the aircraft.

The aircraft can be guided in this direction until it is positioned at a capture point position B known relatively close to the runway. In one embodiment the capture point B is approximately aligned with the return point A and the position of the distance measuring device E, when the azimuth to be followed by the aircraft is aligned with the RA axis. Alternatively, the azimuth to follow can be spaced from the axis AE and the capture point B will then be spaced from said axis and not aligned with the return point A and the position of the distance measuring device E.

From this capture point B in a known position, a predefined path can be imposed on the aircraft so as to bring it to a predetermined point of hooked C approximately aligned with the axis of the runway, with a propagation direction of the aircraft also aligned with the axis of the track. The point of hooked C may be located in periphery of a gripping zone terminus or D-centered on the position of the distance measuring device E and predetermined radius, as shown in Figure 1. For example, such a gripping zone may have a radius less than or equal to 5 km.

The assistance landing system 3 may also comprise one or more additional systems to detect the position of the aircraft to the capture point B.

The landing assistance system may thus comprise an optronic 6 comprising an image capture device 14 on board of the aircraft and an image processing device 19 suitable for the treatment of said image system, connected to the device processing 2. The image processing device is configured to detect any type of object defined characteristics (characteristics

geometric, luminous characteristics, heat signature, etc.) and to define an angular position relative to a reference axis (for example with respect to the axis of movement of the aircraft through the center of the captured image or any position defined in this image). This capture device and image processing device associated can be used for detecting a ground point located in the capture point B or in the vicinity thereof. Such ground mark is called bitter and may for example consist of a building, marking or geographic reference such as a crossroads. The detection of this marker in the images captured by the image capture device can determine when the aircraft is situated approximately at the point of capture B. The field of vision of the image capturing device is not necessarily centered on the axis of movement of the aircraft. The angle between the axis of movement of the aircraft and the axis connecting the image pickup device and a predetermined point of the images captured by the device, for example the center, can be determined by construction or by calibration to to know the direction of propagation of the aircraft with respect to images captured by this device. This direction can be materialized in captured images if it is part of the device's field of view and is known in the image processing device. aircraft and the axis connecting the image capturing device and a predetermined point of the images captured by the device, for example the center, can be determined by construction or by calibration to ascertain the propagation direction of the aircraft relative to images captured by this device. This direction can be materialized in captured images if it is part of the device's field of view and is known in the image processing device. aircraft and the axis connecting the image capturing device and a predetermined point of the images captured by the device, for example the center, can be determined by construction or by calibration to ascertain the propagation direction of the aircraft relative to images captured by this device. This direction can be materialized in captured images if it is part of the device's field of view and is known in the image processing device.

Positioning the aircraft in the capture point B can also be determined from a measurement of distance between the aircraft and a reference point on the ground aligned with the return point A and the position of the distance measuring device E. this reference point on the ground can for example be the position of the distance measuring E itself. distance data between the aircraft and the position of the distance measuring device can be determined by the ground station, based on the transmission time of a signal between the ground station and aircraft or alternatively using from another system such as a radar, then this distance data may be transmitted to the aircraft via the link control / control 1 1. Alternatively, as shown in Figure 2, the aircraft may estimate itself the distance separating it from the ground station. The support system 3 may then comprise a distance estimation unit 5 on board the aircraft and responsible for estimating the distance between the aircraft and the ground station. This module can be integrated to the processing device 2. The distance estimation unit may estimate the distance by measuring the propagation time of at least one data packet between the aircraft and the ground station on the binding of control / command 1 1 or on the mission link 12. Alternatively, the distance estimation unit may include or be connected to an additional transceiver on-board dedicated to the exchange of data packets with the ground station for measuring the distance between the aircraft and the station; the distance estimation module can then estimate the distance by measuring the propagation time of at least one packet of data between the aircraft and the ground station by means of this additional transceiver. The data packets transmitted between the aircraft and the ground station may be stamped so that a delay in one way can be determined between the aircraft and the ground station. The aircraft can then embed a clock synchronized with a clock in the ground station. aircraft and the ground station may be stamped so that a delay in one way can be determined between the aircraft and the ground station. The aircraft can then embed a clock synchronized with a clock in the ground station. aircraft and the ground station may be stamped so that a delay in one way can be determined between the aircraft and the ground station. The aircraft can then embed a clock synchronized with a clock in the ground station.

Positioning the aircraft in the capture point B can also be determined by calculation from data speeds of the aircraft relative to the ground, the distance traveled by the aircraft from the return point A. These speed data can be obtained through the optronic 6 or by a velocity measurement by another vehicle equipment system as described above, for example, by a measure of Doppler effect on electromagnetic waves exchanged over one of the two links data, or else by a velocity measurement with one or more additional dedicated devices on board the aircraft. For example, a pitot probe can be used for measuring the relative velocity of the aircraft relative to the ambient air, another sensor, for example located at the ground station,

The landing assistance system 3 may include an additional positioning system dedicated to the guidance of the aircraft in the bonding during a landing phase until the end point area.

In a first embodiment, the assistance system to the landing 3 comprises a board camera 10 on board the aircraft on which the image processing device can be connected. Such a camera may be an infrared camera pans e.g. type SWIR ( "Short Wave Infrared Range", of wavelength between 0.9 and 1 .7 microns), MWIR ( "Wave Infrared Range Medium") or LWIR ( "Long Wave Infrared Range "). It can also operate in the visible spectrum. This camera 10 may be confused with the image capture device 14 or be separate. The video stream acquired by the camera is transmitted firstly to the image processing device 19 in order to identify the runway and to determine, via the processing device 2, the position of the aircraft with respect thereto upon landing, and secondly to the ground station by means of the "mission" link. In one embodiment, the camera consists of an image capture system may include several optical fields, several spectral bands of detection even more of the tasks functions of the image sensors that are assigned to it. The image processing system is configured to combine an analysis of all images according to known methods. image functions of the missions assigned to it. The image processing system is configured to combine an analysis of all images according to known methods. image functions of the missions assigned to it. The image processing system is configured to combine an analysis of all images according to known methods.

In a second embodiment shown in Figure 4, the landing assistance system 3 includes at least a transceiver positioned on the ground and an on-board transceiver 15 of the aircraft and configured to be connected to the device of data processing 2. such transceivers may be radio beacons UWB (Ultra wide band). By exchanging signals with the one or more transceivers to the ground, the on-board transceiver is capable of determining the distance separating it from each of the transceivers on the ground, for example by measuring the transmission time of return 'a signal. The on-board transceiver is also configured to transmit these distances to the processing device 2. Knowing the positions of the transceivers to the ground, 2 the processing device may then determine a position of the corrected aircraft from the azimuth and elevation data transmitted by the distance measuring device and the distance data provided by the on-board transceiver. In practice, a position of the aircraft can be estimated in this way with at least four transceivers or at least three transceivers more altitude information of the aircraft provided by the altimeter.

The process steps are described in more detail in the following paragraphs, referring to Figure 5.

The method may include a phase support to return navigation P1 during which the processing device carries out the guidance of the aircraft along a predetermined trajectory of the return point A to the point of hooked predetermined C approximately aligned with the axis of the runway, from altitude data provided by the altimeter 4, heading data and speed of the aircraft and variance data (including azimuth and if any elevation) transmitted by the deviation measurement.

The method may also include a phase of assistance landing P2 during which the processing device carries out the guidance of the aircraft to the point of hooked C at the end point D located on the runway.

The phase of P1 navigation assistance may comprise a first guiding step E1 of the aircraft of the return point A towards the position of the distance measuring device E, from azimuth deviation measurements with respect to a reference direction transmitted by the distance measuring device. For this, the AE direction connecting the return point A and the position of the distance measuring device E can be taken as the reference direction and measuring the actual azimuth of the aircraft measured at each instant by the distance measuring device can be used by the latter to determine at any moment the difference between the measured azimuth and the reference direction. The distance measuring device can then transmit at each moment the data processing device via a data link away from azimuth calculated. The processing device may then at each instant guiding the aircraft so as to eliminate this difference, in turn follow the aircraft the reference direction directing it towards the position of the distance measuring device E. The first E1 guiding step may comprise a position determination of the aircraft to the point B of predetermined capture approximately aligned with the return point a and the position of the distance measuring device E. the processing device can determine when the aircraft, the actual position is unknown since leaving the return point A, reaches the capture point B in a known position.

As explained above, the positioning of the aircraft to capture point B can be determined from distance data between the aircraft 1 and a point of ground reference aligned with the return point A and the position of the 'distance measuring E, such that E itself. The positions of the distance measuring device E and the catching point B being known and the aircraft being aligned with these two points, the processing device can from the distance data between the aircraft and the distance measuring deduce the distance between the aircraft and the capture point B. When this distance is zero, the aircraft is located in the capture point B, the uncertainty of the measurements.

These distance data can be received by a bidirectional radio link from the ground station. These distance data can also be determined by the processing device itself, from measurements of the propagation time way or roundtrip between the aircraft and the ground station.

Alternatively, the distance data may be determined by determining a position of the aircraft from a controlled variation of azimuth

the aircraft, or elevation of the aircraft when the latter is close enough to the ground station. Such controlled variation can be induced by a UAV located in the ground station. For this, the aircraft can for example perform a predetermined altitude variation, controlled using the measurements of the altimeter. Such a variation causes a variation in elevation of the measurement data obtained by the distance measuring device. This variation makes it possible to determine the position of the aircraft and therefore the distance at which the aircraft is the position of the distance measuring device E.

Determining the positioning of the aircraft to the capture point B may comprise the data rate estimation of said aircraft and determining a distance traveled by the aircraft from the return point A from said velocity data, example by performing integration during movement of the aircraft. The positions of the return point A and the catching point B being known and the aircraft being aligned with these two points, the processing device can from the distance data between the aircraft and the return point A deduct distance between the aircraft and the capture point B. When this distance is zero, the aircraft is located in the capture point B, the uncertainty of the measurements.

The aircraft velocity data can be estimated by the optronic system 6 by measuring the running speed of the floor using the images captured by the image capture device and altitude data provided by 'altimeter.

aircraft velocity data may also be estimated by measuring a Doppler effect caused by movement of the aircraft. For example, the data processing device may measure a frequency shift induced by the movement of the aircraft in the signals received on one of the two data links from the ground station and the distance measuring device.

The aircraft velocity data can also be measured by another vehicle system such as pitot probes. Such probes measuring only the speed of the aircraft relative to the ambient air and thus can not accurately reflect the speed of the aircraft relative to the ground in case of wind, these data may be supplemented by information from ambient wind speed along the trajectory followed by the aircraft. This velocity information can be determined by a weather station, integrated with the ground station according to known methods.

Determining the positioning of the aircraft to capture point B can also be determined by detection of a bitter known position in at least one image captured by said image capture device, as described above, supplemented the altitude data of the aircraft provided by the altimeter. The image capture device may also be used to detect a bitter known position before the aircraft arrives in the vicinity of the catching point B, during the path from the return point. Such detection can be used to check and if necessary correct, the distance between the current position of the aircraft and the capture point B determined by the means described above.

Such bitter for determining the positioning of the aircraft to the capture point B may be the position E of the distance measuring device itself. During the first step E1 guide the aircraft runs to effect the position of the distance measuring device E which is therefore situated in the axis of propagation of the aircraft and in the field of the optoelectronic system. The optronic system is able to detect in the images of the image capture device the distance measuring device at a distance of approximately 1 to 2 km. The distance measuring device being located generally near the runway, the aircraft is then at a comparable distance therefrom and adapted to implement a predetermined movement to the point of hooked C so as to align the aircraft with the runway centreline of landing. The hanging point C may also be coincident with the position of the distance measuring E if it is approximately aligned with the axis of the track.

In different modes of determining the positioning of the aircraft to capture point B involving the optronic system, it can use images from the camera, for example in case of failure of the image capturing device 14.

Upon such determination of the positioning of the aircraft capture point B depending on the position of the distance measuring device E, knowledge of the absolute geographical coordinates of the capture point B, the point of hooked C and position the distance measuring device E is not required. Knowledge of the relative positions of these points with each other and with respect to the landing strip is sufficient to effectively guide the relative way of aircraft with respect to the track and position it correctly for landing. This can be particularly useful when the runway is temporary and that the conditions, such as no GPS signal, for example, make delicate precise positioning of the track. In addition, no

Another reference point is necessary for the proper functioning of the optronic system and the guidance of the aircraft.

Determining the positioning of the aircraft to capture point B can finally be determined by determining the position data of the aircraft as the longitude and latitude. The satellite location data is unavailable, the position of the aircraft can be determined from:

• the azimuth measured by the distance measuring device, and

• Two data from:

o the elevation of the aircraft measured by the distance measuring device,

o the distance between the aircraft and the distance measuring device, determined as indicated above,

o the altitude of the aircraft with respect to the distance measuring device obtained from the measurements of the altimeter.

The calculation of position data with measurements transmitted by the distance measuring device can be achieved in polar coordinates centered on the position of the distance measuring device E, then the aircraft position data obtained can be converted to Cartesian coordinates in form of longitude and latitude.

At the end of the first step E1 guide the aircraft is thus positioned to capture point B. The phase of assistance to return navigation P1 may then comprise a second E2 step of guiding the aircraft along a predefined path of the catching point B to point C hung approximately aligned with the axis of the runway. Along this predetermined trajectory, the aircraft may be deviated from the theoretical path to be followed by the wind. To correct the position of the aircraft to maintain the predefined path, the guidance of the aircraft can be made from altitude data provided by the altimeter and heading and speed data of the aircraft .

During this first step guide E1, the predefined trajectory followed by the aircraft between the return point A and point B of capture may be rectilinear in the direction of the position of the distance measuring device, thereby minimizing the distance traveled and energy consumed to reach the capture point B.

Alternatively, the predefined trajectory followed by the aircraft between the return point A and point B of capture may be zigzag or bearings. Such path then allows for slightly varying the orientation of the position of the directional antenna of the ground station and thus reduce the uncertainty about the azimuth and / or elevation measured by the distance measuring device.

The steps described above allow to obtain the position of the aircraft with sufficient accuracy to achieve the aircraft into alignment with the runway to the point of hooked C. However the accuracy obtained may be insufficient to guide the aircraft to the endpoint and land it on the airstrip. With insufficient positioning accuracy, the aircraft may be guided next to the track. It may therefore be desirable to obtain the position of the aircraft with increased accuracy ensuring a safe landing.

In a first embodiment, shown in Figure 5 and in Figure 6, the phase of assistance landing P2, during which the aircraft is guided to the point of hooked C at the end point D, may use the images of the runway and landing point D provided by the onboard camera 10 on board the aircraft. For this, the assistance phase landing P2 may comprise an E3 image processing step in which the position of the end point D is estimated in one or more images from the stream of images of the airstrip successively captured by the camera. This step can be carried out repeatedly throughout the approach of the aircraft to the runway and landing.

This detection of the end point in an image can be fully automated if the end point is easily detectable in the image,

example, if the end point is materialized on the runway by a ground reference, or if the track itself is detectable by the presence in soil of one or more pins such as markings or visible lights in the spectral band of optronic system. The position of the end point in the image can then be determined by known techniques of pattern recognition or image.

Alternatively, end point of the position in an image can be specified by a human operator in a first image, through the connection control / order 1 1, for example by positioning the image in a crosshair on the end point, as shown in Figure 7. Then, the processing device can ensure tracking ( "tracking") of the position of the end point pointed at by the reticle in the images subsequently provided by the onboard camera, and adjust automatically the position of the reticule to keep focused on the end point. Such tracking of manual initiation may be necessary when marking the airstrip or landing point is insufficient for automatic detection, or when the flight conditions (night, rain, fog ...) do not allow such automatic detection. If necessary, the operator can correct the position tracking by manually adjusting one or more times the position of the reticle in the current image so that the reticle remains positioned on the end point in successive images processed. To facilitate the automatic tracking of the position of the end point, visible or infrared light sources, adapted to the detection spectrum of the image capture system may be disposed on either side of the runway at height the end point. operator can correct the position tracking by manually adjusting one or more times the position of the reticle in the current image so that the reticle remains positioned on the end point in successive images processed. To facilitate the automatic tracking of the position of the end point, visible or infrared light sources, adapted to the detection spectrum of the image capture system may be disposed on either side of the runway at height the end point. operator can correct the position tracking by manually adjusting one or more times the position of the reticle in the current image so that the reticle remains positioned on the end point in successive images processed. To facilitate the automatic tracking of the position of the end point, visible or infrared light sources, adapted to the detection spectrum of the image capture system may be disposed on either side of the runway at height the end point.

CLAIMS

1. Method for assisting in the landing of an aircraft (1) on a runway from a return point (A) to an end point (D) at which the aircraft comes into contact with the runway,

said method being implemented by a data processing device (2) on board said aircraft (1) and configured to be connected to:

- an altimeter (4) configured to measure the altitude of the aircraft,

- a distance measuring device (13) positioned at a ground station and configured to measure an azimuth deviation of the aircraft relative to a reference direction connecting said return point (A) and the position of the distance measuring device (E),

said method being characterized in that it comprises:

- a phase of assistance for return shipping (P1) including:

- a guidance of the aircraft (1), from azimuth deviation of the aircraft measures with respect to said reference direction transmitted by the distance measuring device, since the return point (A) towards the position of the distance measuring device (E);

- a position determination of the aircraft at a predetermined capture point (B) aligned with the return point (A) and the position of the distance measuring device (E);

- a guidance of the aircraft (1) along a predefined path from the capture point (B) to a hanging point (C) aligned with the predetermined axis of the runway from elevation data provided by the altimeter (4) and data heading and speed of the aircraft;

- a landing assistance phase (P2) comprising a guide of the hanging point (C) at the end point (D) located on the runway.

2. A supporting method according to claim 1, wherein the positioning of the aircraft to the capture point (B) is determined from distance data between the aircraft (1) and a reference point on the ground aligned with the return point (A) and the position of the distance measuring device (E).

3. A supporting method according to claim 2, wherein said distance data are estimated from measurements of the propagation time of data packets between the ground station and the aircraft.

4. A supporting method according to claim 3, wherein said distance data are estimated from measurements of the propagation time of forward packet

data between the ground station and the aircraft, said ground station and aircraft comprising synchronized clocks.

5. A supporting method according to claim 1, wherein determining the position of the aircraft to the capture point (B) comprises the speed data estimation of said aircraft and determining a distance traveled by the aircraft from the turning point (A) from said speed data.

6. A supporting method according to claim 5, wherein the data processing device (2) being configured to be also connected to an electro-optical system (6) comprising a device for capturing images (14) embedded in the aircraft (1) and positioned along the axis of the aircraft, and an image processing device adapted for processing said images, speed data of said aircraft (1) are estimated by said optronic system by measuring floor frame rate using images captured by said image capture device and altitude data provided by the altimeter (4).

7. A supporting method according to claim 5, wherein said speed data of said aircraft (1) is estimated by measuring a Doppler effect caused by movement of the aircraft on signals exchanged between the aircraft and the station on the ground.

8. A supporting method according to one of claims 1 to 7, wherein the data processing device (2) being configured to be also connected to an image capture device installed in the aircraft (1) the positioning of the aircraft to the capture point (B) is determined by the detection of a bitter known position in at least one image captured by said image capturing device.

9. A supporting method according to one of claims 1 to 8, wherein the aircraft (1) is guided between the return point (A) and the capture point (B) along a straight predetermined path in the direction of the position of the distance measuring device (E).

10. A supporting method according to one of claims 1 to 8, wherein the aircraft (1) is guided between the return point (A) and the capture point (B) in a zigzag path or bearings .

January 1. A supporting method according to any one of claims 1 to 10, wherein the data processing device (2) configured to be also connected to a camera (10) embedded in the aircraft (1), the phase of the landing assistance (P2) comprises estimating (E3) from a position of the end point (D) in an image of the airstrip captured by the camera (10) and the estimate (E4) from a position of the aircraft as a function of said position of the estimated finishing point in the image and altitude data provided by the altimeter (4), and wherein said guiding of the aircraft the hanging point (C) at the end point (D) is performed by maintaining the aircraft aligned with the axis of the runway.

12. A supporting method according to any one of claims 1 to 1 1 wherein the data processing device (2) being further configured to be connected to an on-board transceiver (15) on said aircraft (1 ) and for receiving signals from at least three transceivers positioned on the ground, the landing assistance phase (P2) comprises estimating (E7) position data of the aircraft from data distances between the on-board transceiver (15) and said at least three transceivers on the ground.

13. A supporting method according to one of claims 1 to 12, wherein the aircraft (1) is further guided from difference of elevation of the aircraft measures with respect to a reference plane.

14. A computer program product comprising code instructions for executing a method according to any one of claims 1 to 13 when this program is executed by a processor.

15. A data processing device (2) configured for implementing the assistance method according to one of claims 1 to 13.

16. Automatic Assist landing (3) of an aircraft (1) on a runway from a return point (A) to an end point (D) at which the aircraft comes into contact with the runway comprising:

- an altimeter (4) configured to measure the altitude of the aircraft,

- a distance measuring device (13) positioned at a ground station and configured to measure relative to a reference point an azimuth deviation of the aircraft relative to a reference direction connecting said return point (A) and the position of the distance measuring device (E),

-The data processing device (2) according to claim 15.

17. Support system (3) according to claim 16 wherein the distance measuring device

(13) is connected to a directional antenna.

18. Support system (3) according to claim 16 or 17 further comprising an electro-optical system (6) comprising an image capture device (14) embedded in the aircraft (1) configured to be connected to the device data processing system (2), and also configured to implement a method according to any one of claims 1 to 12 in combination with claims 6 or 8.

19. Support system (3) according to one of claims 16 to 18 further comprising a camera (10) and image processing device associated with, configured to be connected to the data processing device (2), and also configured to implement a method according to any one of claims 1 to 12 in combination with claim 1 1.

20. assistance system (3) according to one of claims 16 to 18 further comprising:

- at least three transceivers positioned on the ground;

-a transceiver (15) configured to receive signals emitted by said at least three transceivers positioned on the ground, on board said aircraft (1) and configured to be connected to the data processing device (2),

said elements being configured to implement a method according to any one of claims 1 to 12 in combination with claim 12.