Abstract:
The present invention relates to a method and a system for assisting in the landing or the decking of a light aircraft, the method being implemented by a system comprising a device on the ground for locating the aircraft, the aircraft having an onboard signal sender, the method comprising at least the following steps: the locating device on the ground uses signals sent by the sender to determine the position and/or movement of the aircraft; said device transmits the previously determined aircraft position and/or movement data to the aircraft; display means show at least some of said data made accessible to the pilot of the aircraft. The invention applies in particular to the field of civil light aeronautics, notably for facilitating the landing of pleasure aeroplanes, small transport aeroplanes and helicopters.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to foreign France patent application No. 0902475, filed on May 20, 2009, the disclosure of which is hereby incorporated by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method and a system for assisting in the landing or the decking of a light aircraft. It applies in particular to the field of civil light aeronautics, notably to facilitate the landing of pleasure aeroplanes, small transport aeroplanes and helicopters. 
       BACKGROUND OF THE INVENTION 
       [0003]    Among the aircraft landing assistance systems, the best known are the ILS systems, ILS standing for “Instrument Landing System”. ILS systems are instrument approach systems for aircraft equipped therewith. An ILS system supplies information assisting the pilot in his landing manoeuvre. Such systems therefore require specific instrumentation on board the aircraft as well as detection and guidance systems on the ground. 
         [0004]    Another guidance system employed at airports is the MLS, MLS standing for “Microwave Landing System”. It provides precision guidance for a landing, regardless of the meteorological conditions. 
         [0005]    The ILS and MLS systems are very expensive and bulky items of equipment both on the ground and on board the aircraft. Light aircraft cannot include the equipment needed to implement these systems as much for cost reasons as for lack of space. 
         [0006]    Apart from these conventional means that are primarily used by commercial civil aviation, other solutions can be envisaged. 
         [0007]    A first solution uses a satellite positioning system, this type of system being commonly designated by the acronym GNSS, standing for “Global Navigation Satellite System”. Among these positioning systems, the GPS system, GPS standing for “Global Positioning System”, is now the most widely used. The main drawback of the GNSS systems is their lack of robustness. In practice, this type of service is not always available and is sensitive to electromagnetic interference. 
         [0008]    A second solution is to use a LIDAR system, LIDAR standing for “Light Detection And Ranging”. This locating system, which operates on the same principle as radars, uses lasers in the visible range, and even in the infrared range. This therefore makes it ineffective in unfavourable weather conditions. 
         [0009]    Another solution consists in using a highly directional millimetre-wave radar. Millimetre-wave radars require a search phase to designate the target. They must also be positioned accurately relative to the runway. This solution is, furthermore, very costly and often requires an onboard responder on the aircraft. The responder is itself costly, bulky and heavy, and it consumes a lot of energy. It also has to be made redundant for operational safety reasons. 
         [0010]    Other locating methods for automatically guiding unmanned aircraft have been proposed in the past. Notable among these is the international patent application referenced by the number WO2006/053868, which notably proposes using a radar on the ground and a multifunction beacon on board the aircraft. However, this method does not solve the problem of assisting in the landing of manned aircraft, notably when the environmental conditions are unfavourable, for example when visibility is almost zero in foggy weather. 
         [0011]    One technique described in the international patent application WO 02/091595 makes it possible to guide an aircraft in the landing phase using an interrogator-responder exchange between the ground and the aircraft. However, this synchronous system requires significant specific equipment, both on the ground and on the aircraft. Furthermore, this system suffers from a significant blind spot close to the secondary radar on the ground and implementing such a system is complex because of the accuracy required. 
       SUMMARY OF THE INVENTION 
       [0012]    One aim of the invention is to propose an inexpensive method for facilitating the landing of a manned light aircraft. To this end, the subject of the invention is a method for assisting in the landing or the decking of a manned aircraft, the aircraft being of the engine-powered light aircraft type suitable for visual flight, the method being implemented by a system comprising a device on the ground for locating the aircraft, comprising at least one sensor and a reference beacon, the aircraft having an onboard sensor sending signals asynchronously to the device on the ground, the method being characterized in that it comprises at least the following steps:
       the locating device on the ground uses signals sent by the sender to determine the position and/or the movement of the aircraft;   said device transmits the previously determined aircraft position and/or movement data, for example via a radiofrequency link, to the aircraft;   display means in the aircraft or radio communication means in the aircraft show the pilot of the aircraft at least some of said data to assist in the landing or the decking.
 
The expression “locating device” should be understood to mean a device suitable for measuring the position of the aircraft but not only for that. In practice, such a device can also measure other parameters such as the radial speed of the aircraft. As an example, the data transmitted to the aircraft by the device on the ground include the position of the aircraft, its radial speed, the barometric pressure measured on the ground. The pilot always remains in control of the manoeuvres performed because the system according to the invention does not act on the aircraft controls; it provides the pilot with additional information and increases the reliability of the information already available with the onboard instruments.
       
 
         [0016]    The expression “light aircraft” should be understood to mean an aircraft whose certified maximum capacity recorded in the airworthiness documents associated with the aircraft is less than 10 seats, apart from the pilot seats, or a rotorcraft whose certified maximum capacity recorded in the airworthiness documents associated with the aircraft is less than 6 seats apart from the pilot seats, or an aeroplane whose certified maximum weight on take-off is less than 6000 kg, or a rotorcraft whose certified maximum weight on take-off is less than 3000 kg. 
         [0017]    Advantageously, the onboard sender in the aircraft sends a continuous sinusoidal signal. 
         [0018]    The method according to the invention can also comprise a step of correlating data obtained from the device for locating the aircraft from the ground with the data produced by the onboard instruments, the results of this correlation step being utilized on board the aircraft. Such correlated data can then be displayed, and, for example, be used to consolidate the data obtained from the onboard instruments. This correlation step can notably be used to detect an anomaly in the measurements taken by the onboard instruments. 
         [0019]    According to one embodiment of the method according to the invention, a data consistency index is determined from the correlation step, and an alarm is raised for the pilot when said index is below a set threshold. 
         [0020]    A bidirectional radiofrequency data link can be set up between the locating device on the ground and the aircraft, the measurements obtained from instruments on board the aircraft being transmitted to the locating device on the ground via said data link, said device on the ground utilizing said measurements to refine its determination of the data relating to the position and/or the movement of the aircraft. For example, the “wind” speed estimated from the aircraft may be transmitted to the ground. Analyses can be performed on the ground, so as to generate a reliability index and raise an alert in the event of an anomaly. 
         [0021]    According to one embodiment of the method according to the invention, the aircraft inserts, from the data sent to the locating device on the ground, an identifier specific to the aircraft, said device inserting in return said identifier from the data transmitted to the aircraft. The use of this identifier as a signature makes it possible to accept, on the aircraft, only the data that is intended for it without being disturbed by data intended for other aircraft. 
         [0022]    Another subject of the invention is a system for assisting in the landing or the decking of a manned aircraft, the aircraft being of the engine-powered light aircraft type suitable for visual flight, the system comprising a device on the ground for locating the aircraft provided with a sensor and a reference beacon, the system comprising at least one onboard sender sending signals asynchronously from the device on the ground, means for transmitting data from the locating device to the aircraft and, in the cockpit of the aircraft, means for displaying said data transmitted to the aircraft. 
         [0023]    The system according to the invention may comprise an onboard processing module linked to the data transmission means, to the display means and to onboard measuring instruments, the processing module being suitable for correlating the measurements obtained from said onboard instruments with the measurements obtained from said data transmission means. 
         [0024]    According to one embodiment of the system according to the invention, the display means are a screen associated with a standby instrument integrated in the aircraft. The data can be transmitted to the integrated standby instrument via a standard bus, for example of ARINC 429 type. 
         [0025]    The system according to the invention can also comprise onboard data sending means in the aircraft, said sending means coupled with the transmission means being used to set up a bidirectional link between the locating device on the ground and the aircraft. 
         [0026]    According to one embodiment of the system according to the invention, the onboard data transmission means and the onboard sender are integrated in one and the same multifunction beacon. Similarly, the multifunction beacon can comprise sending means and a processing module when these means are implemented by the system. 
         [0027]    According to one embodiment of the system according to the invention, the locating device on the ground comprises at least two passive sensors that are spaced apart, fixed close to the decking surface and able to receive the signals sent by the aircraft. This embodiment makes it possible notably to locate the aircraft by triangulation. Furthermore, the passive nature of the sensors means that signals that might be detrimental to the health of people on the ground are not sent. 
         [0028]    Advantageously, the system according to the invention applies to aircraft that do not include any instrument landing system, i.e. any ILS system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    Other features will become apparent from reading the following detailed description given as a nonlimiting example in light of the appended drawings, in which: 
           [0030]      FIG. 1   a  represents a block diagram showing a first exemplary architecture of the system according to the invention, 
           [0031]      FIG. 1   b  represents a block diagram showing a second exemplary architecture of the system according to the invention, 
           [0032]      FIG. 1   c  represents a block diagram showing a third exemplary architecture of the system according to the invention, 
           [0033]      FIG. 2   a  represents a first exemplary locating device on the ground used by the system according to the invention, 
           [0034]      FIG. 2   b  represents a second exemplary locating device on the ground used by the system according to the invention, and 
           [0035]      FIG. 3  represents an exemplary artificial horizon display device integrated in a system according to the architecture shown in  FIG. 1   a.    
       
    
    
     DETAILED DESCRIPTION 
       [0036]    In the interests of clarity, identical references in the various figures denote the same elements. 
         [0037]      FIG. 1   a  shows, through a block diagram, a first exemplary architecture of the system according to the invention. The system  100  comprises, on the ground, a device  102  for locating the aircraft  104 . The aircraft  104  comprises a standby instrument  142 , commonly designated ESI, standing for “Electronic Standby Instrument”, or IESI, standing for “Integrated Electronic Standby Instrument”. This instrument  142  is supplied by onboard or integrated measuring means  144  comprising, for example, sensors, inertial probes and/or accelerometers and can be used, via a screen  160 , to display the basic navigation parameters supplied by said measuring means  144 , at least the altitude of the aircraft  104 , its speed and its attitude. 
         [0038]    Unlike a conventional configuration, the IESI  142  is, in the system according to the invention, also supplied by the device  102  for locating the aircraft  104 . The locating device  102  utilizes a signal  152  obtained from an onboard sender  146  on the aircraft  104  to determine, notably, the position of this aircraft  104 . The locating device  102  then transmits this position—and other parameters, where appropriate—to the aircraft  104 , via a radiofrequency link  154  set up between a sender on the ground  121  and onboard reception means  148 , for example an antenna receiver, suitable for receiving the parameters. The data obtained from the locating device  102  are then utilized on board the aircraft  104 . 
         [0039]    For example, these data are displayed and/or correlated with the data already available on board. To correlate the data, the system may include, on board the aircraft  104 , a processing module  145 , for example a microcontroller, able to receive both data obtained from the instruments on board the aircraft  104  and data obtained from the locating device  102  and transmitted by the reception means  148 . The data correlation is used notably to produce reliability indices concerning the measurements. Examples of possible correlations notably include comparing speeds and altitudes measured on the ground with those measured by the onboard instruments. When abnormal discrepancies appear, an alert can be raised for the pilot. The IESI  142  is, in the example, supplied by the processing module  145 ; however, the IESI  142  can also be supplied directly by the data obtained from the device  102  on the ground and transmitted by the reception means  148 . 
         [0040]    According to one embodiment of the system according to the invention, data sending means  148 ′, for example an antenna sender, are coupled to the reception means  148  to make it possible to set up a bidirectional radiofrequency link  154 ,  156  with the locating device  102  on the ground. Thus, data such as the measurements taken by the instruments specific to the aircraft  104  can be transmitted to the ground to be utilized. The locating device  102  on the ground can, by virtue of these onboard data, refine or correct the measurements taken on the ground. The locating device  102  on the ground can, for example, include analysis software capable of comparing the data obtained from the aircraft and the data measured on the ground. In the event of an anomaly—for example, if the descent gradient of the aircraft  104  is too steep—an alert can be raised and sent to the pilot and/or to the controller. According to another embodiment, the sender  146  is used to send data to the ground, according to a principle already described in the international patent application referenced by the number WO 2007/063126. 
         [0041]    Advantageously, the aircraft  104  has a multifunction beacon  149  on board comprising the processing module  145 , the sender  146 , the reception means  148  and, when they exist, the data sending means  148 ′. Thus, by combining the onboard elements necessary to the operation of the system in one and the same beacon  149 , the hardware impact on the aircraft  104  is minimized. For example, when there is a multifunction beacon  149  suitable for operating in send and receive modes behind the blades of a helicopter, said multifunction beacon  149  can be fixed to the windshield of the aircraft  104 , which avoids the integration constraints specific to the cockpit of the aircraft  104 . 
         [0042]    Advantageously, the sender  146  transmits an identifier to the ground that is used to differentiate the data sent by the aircraft  104  from the data possibly sent by other aircraft, this identifier possibly, for example, being specific to the multifunction beacon  149  when such a beacon is on board the aircraft  104 . This identifier is then, for example, coded in the data sent by the locating device  102  to the aircraft  104 , so that, if several aircraft equipped with the system according to the invention receive said data, only the aircraft  104  for which these data are intended takes them into account. 
         [0043]    In the absence of reception means  148  or if said reception means fail, the VOR/DME (VHF Omnidirectional Range/Distance Measuring Equipment) beacon conventionally available on an aircraft  104  can be used to receive the signals sent by the device  102  on the ground. 
         [0044]      FIG. 1   b  shows, through a block diagram, a second exemplary architecture of the system according to the invention. According to this embodiment, the data obtained from the locating device  102  on the ground are displayed on a dedicated screen  160 ′, independent of the IESI  142 . The information delivered to this dedicated screen  160 ′ is supplied to the pilot as a complement to data displayed on the screen  160  of the IESI  142 . The multifunction beacon  149  is linked to the dedicated screen  160 ′. According to an alternative embodiment, the dedicated screen  160 ′ can be integrated in the multifunction beacon  149  when said beacon can be positioned so as to offer the pilot satisfactory visual access. 
         [0045]    Furthermore, operation powered by battery and/or by a generator of the aircraft  104  can be envisaged, because of the system&#39;s lower energy consumption requirement. 
         [0046]      FIG. 1   c  shows, through a block diagram, a third exemplary architecture of the system according to the invention. According to this embodiment, a satellite positioning terminal  170 , for example a GPS terminal, is available and the screen of this terminal  170  is used to display the data obtained from the locating device  102  on the ground. In the example, the sender  146  is used both to send signals intended to facilitate the detection of the aircraft  104 , but also to send data to the locating device  102  on the ground; in other words, the sender  146  also fulfils the functions of the data sending means  148 ′ of  FIG. 1   a.    
         [0047]    The data obtained from the locating device  102  on the ground can be compared to the data supplied by the satellite positioning terminal  170 . The terminal  170  can supply measurements of medium reliability, in particular for the altitude measurements. Also, it may be useful to correlate these measurements with those obtained from the locating device  102  on the ground. Notably, since the data measured on the ground may also be affected by a bias, it may be wise the utilize the trend of the measurements produced by the device  102  on the ground to correct the measurements obtained via the onboard satellite positioning system. According to one embodiment of the system according to the invention, the data supplied by the terminal  170  are also consolidated by virtue of the sensors  172  integrated in the multifunction beacon  149 . For example, if this beacon  149  comprises a proximeter, an altitude measurement obtained from a baroaltimeter  144  of the aircraft  104  can be consolidated for the pilot based on the measurement obtained from the device  102  on the ground and the measurement obtained from the proximeter  172  of the beacon  149 . A reliability index or likelihood coefficient, dependent on the level of correlation between the measurements, may also be supplied to the pilot. All the indications obtained from the system according to the invention are naturally optional, the display of the indications being, moreover, deactivated when the likelihood coefficient falls below a minimum threshold. 
         [0048]    In a degraded mode in which the reception means  148  are non-existent or have become inoperative, the data obtained from the ground may be transmitted to the aircraft  104  via a radio link to inform the pilot through audible commands, which can be pre-recorded or frequency-coded. For example, the commands can be pre-recorded in the form of words such as “up”, “down”, “left”, “right”, “OK”, so as to guide the pilot when the latter has to put down the aircraft in poor conditions. Repeating the commands every second may guarantee correct operation of the system. Furthermore, a hierarchical structure can advantageously be applied to the transmission of the commands according to their criticality. 
         [0049]    To prevent an even more degraded mode, in which the onboard sender  146  does not operate, a reflector can be fixed to the aircraft  104 , so as to increase its radar cross section and thus facilitate its location using the radar  203  ( FIG. 2   a ) on the ground. For the reflector, it is possible to choose a three-dimensional coordinate system suited to the radar&#39;s sending band, for example to the X band. Adhesive metal strips placed on the fuselage of the aircraft can also be used for these purposes. Once the aircraft  104  has been located, audible commands can be transmitted to the pilot by radio. 
         [0050]    Moreover, in this degraded mode, it is not possible to transmit the identifier associated with the sender  146 . Consequently, to set up an unambiguous link  154  between the device  102  on the ground and the aircraft  104 , the identification will, for example, have to be made via radio messages. A lock-on request can be sent automatically when the aircraft  104  is approaching the device  102  on the ground at a certain distance. The pilot of the aircraft  104  receives commands transmitted by the device  102  on the ground, for example audible commands, and is forced to estimate the quality of his identification by diverting around proposed positions. For example, the announcement of the speed of the craft can usefully be used as a lock-on marker. This speed can be compared to the air speed indicator and modulated to check the match between the received data and the data displayed by the onboard instruments. 
         [0051]      FIG. 2   a  shows a first exemplary locating device on the ground used by the system according to the invention.  FIG. 2   a  shows an aircraft  104  in the landing phase on a landing runway  202 . The locating device  102  notably comprises a radar  203  on the ground and a beacon  205  on the ground, situated at the edge of the runway  202 . A multifunction beacon  149  on board the aircraft  104  and comprising a sender  146  and reception means  148  is also shown in the figure. Such a locating device  102  is notably described in the international patent application WO 2006/053868. The beacon  205  on the ground serves as a reference and can be used to cyclically check the integrity of the locating device  102  on the ground, for example at a rate of 20 times per second. The state of the locating device  102  on the ground can then be uploaded to the aircraft  104 . 
         [0052]      FIG. 2   b  shows a variant of the locating device on the ground used by the system according to the invention. The locating device of  FIG. 2   b  comprises a number of passive sensors—in the example, two sensors  211 ,  212 —and a sending reference beacon  213 . In the example, the sensors  211 ,  212  are antenna panels comprising several blocks of flat antennas on their surface. The decking surface  202   a  is, for example, a runway of width L 1  equal to 20 m and of length L 2  equal to 50 m. These panels  211 ,  212  are, for example, placed at the end of the decking surface  202   a  and in a plane roughly orthogonal to this surface  202   a , so as to radiate towards said surface  202   a . The reference beacon  213  is placed, for example, at the other end of the decking surface  202   a . This reference beacon  213  is used to indicate a constant direction to the sensors  211 ,  212 , to standardize and calibrate said sensors  211 ,  212 , and to avoid the thermal drifts by restandardizing the sensors as the sunlight and/or temperature conditions change. The reference beacon  213  sends a signal towards the sensors  211 ,  212 , for example a continuous sinusoidal signal. The signal sent by the reference beacon  213  has a different frequency from that of the signal sent by the sender  146  on board the aircraft  100 . According to another embodiment in which the sensors  211 ,  212  are optical probes, the reference beacon  213  is a diode or a laser used to calibrate said probes  211 ,  212 , such a beacon  213  making it possible to realign the system in relative mode relative to the decking surface  202   a  and to give a reference (a common “zero”) to the sensors  211 ,  212 . The passive sensors  211 ,  212  are used to locate the aircraft  104  by triangulation. One advantage of this locating device  102  is that it does not require any high power sending from the ground. 
         [0053]    When there are side walls close to the decking surface  202   a , the sensors  211 ,  212  are advantageously angled so that the pairs of blocks  702  of antennas are arranged along an axis  709  forming an angle α of between, for example, 20° and 70° with the vertical axis  705 . The inclinations of the sensors  211 ,  212  may be unequal and in the same direction or in opposite directions (for example −45° for one sensor and 45° for the other). By inclining each sensor  211 ,  212  about a horizontal axis orthogonal to the plane of said sensor, it also becomes possible to perform spatial sampling on the azimuth axis of the amplitude of the interference signal, which consists of the sum of the signal received directly by the sensor  211 ,  212  and of the signal reflected on the lateral partition or partitions then received by the sensor  211 ,  212 . 
         [0054]    Thus, by performing the spatial sampling in two dimensions for each sensor  211 ,  212 , it is possible to identify the point on each sensor  211 ,  212  that corresponds to the interference signal of maximum amplitude and reapply the formulas demonstrated in the international patent application WO 2007/131923. The amplitudes measured on the antennas are a product of a sine function described in that patent application. The inclined positioning of the sensors, and the spatial sampling in two dimensions of the interference signal means that, by using a minimum of antennas, the multiple paths both in elevation and in azimuth can be disregarded. 
         [0055]      FIG. 3  shows an exemplary artificial horizon display device integrated in a system according to the architecture shown in  FIG. 1   a . The IESI  142  of the aircraft  104  comprises a screen  401  displaying several navigation parameters obtained from the measuring means  144  ( FIG. 1 ). The IESI  142  comprises a computer for producing, for the screen  401 , a graphic image representative of these parameters. In the nonlimiting example of  FIG. 3 , an indicator  412  on the left of the screen  401  shows the speed of the aircraft, an indicator  413  on the right of the screen  401  shows the altitude, and the horizontal part  415  shows an artificial horizon. The graphic representation of the various indicators and their layout may differ according to the embodiments. 
         [0056]    In addition to this information already available on the existing systems, the system according to the invention can display, on this screen  401 , the position of the aircraft  104  as determined by the locating device  102  on the ground. For example, this position, in a vertical plane, may be represented by a point  416 , the landing or decking point being represented, for example, by a point  417  situated in the centre of the screen  401 . 
         [0057]    Preferably, the data obtained from the locating device  102  on the ground and transmitted by the reception means  148  to the IESI  142  are formatted according to an aeronautical standard format, for example the “ARINC 429” format. They can also be received via a standard data bus of the IESI  142  and processed easily by the computer of the IESI  142 . The additional information available by virtue of the data supplied by the locating device  102  can be displayed on an additional display page or via an overlay on an already existing page. 
         [0058]    The system according to the invention can also be linked to the air traffic control systems, commonly designated by the acronym ATC, in order to allow civil aeroplanes to be fully integrated in the airport control system. The aeroplanes can, for example, be recognized from 10 km in the axis of the landing runway. The link between the locating device  102  on the ground and the aircraft  104  can, for example, be set up for a distance of 5 km or less, the position and ground speed data being able to be sent to the aircraft  104  in the form of absolute or relative coordinates. 
         [0059]    The system according to the invention can notably be used to facilitate the decking of private helicopters on floating platforms, for example on pleasure ships or in an urban environment, for example on a roof of a building. It applies more particularly to light aviation, that is to say to aircraft that have a flight radius of around a few hundred kilometres, for example private aeroplanes, ULMs, single-engine aeroplanes, light twin-engined aeroplanes. 
         [0060]    More generally, the system according to the invention can be used as a redundant system at airports, including those provided with Class III ILS systems. This system could then be offered to the pilot of the aircraft as a “comfort” option, notably to reduce his stress, notably in case of unforeseen poor visibility on landing. 
         [0061]    One advantage of the system according to the invention is that it requires very few adaptations to the aircraft and little in the way of installations on the ground, which makes it both quick to implement and inexpensive.