Abstract:
A method monitors at least one avionic system connected to a communication medium that includes at least one active communication switch component. The method includes determining a state of the switch component and evaluating an indicator of a state of the communication medium from the state of the switch component and from a predetermined modeling of communication flows of the communication medium. The method also includes selecting and activating an alarm according to the evaluated state of the communication medium and according to a predetermined modeling of consequences of the evaluated state of the communication medium on a function of the at least one avionic system. A corresponding device and a method for determining conditions for alarm activation are also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the reliability of avionic systems and more particularly to a method and a device for monitoring avionic systems connected to a shared medium. 
     2. Discussion of the Background 
     The reliability of avionic systems is at the center of the concerns of aircraft designers. It generally is acknowledged that a redundancy of the key equipment items of aircraft is necessary in order to ensure the required functions despite the failure of one system as well as in order to compare the performance of the systems and to rapidly detect a possible failure. 
     The use of computer systems in aircraft has led the designers to implement computer networks for the transmission of information items and commands among the operational systems. The computer networks here are considered to be shared communication media used to exchange data. The capacity of these media is determined by the characteristics of the transmitted data, in particular their volume and their speed of transmission. 
     In particular in order to meet the increase in the number of transmitted data and the required transmission speeds, it can prove necessary nowadays to use active components in the computer networks, for example switches. The use of active components makes it possible to optimize transfer of the data according to the parameters linked to these data such as their nature and according to the state of the communication network, in particular its load. 
     SUMMARY OF THE INVENTION 
     While the use of passive components in aircraft computer networks is considered to be reliable (the reliability of these components generally is superior to that of the avionic systems), the use of active components can lead to a lowering of the overall reliability of the avionic systems as a result of their reliability. 
     The invention makes it possible to resolve at least one of the problems set forth above. In particular, the invention makes it possible to take into account breakdowns of one component of a shared communication medium in the handling of monitoring of a set of avionic systems performing operational functions, connected to this shared medium. 
     The invention thus has as an object a method for determining the conditions for activation of at least one alarm of at least one avionic system connected to a communication medium comprising at least one component, this method comprising the following steps,
         determining the conditions for activation of the said at least one alarm according to the state of the said at least one avionic system;   determining the conditions for activation of the said at least one alarm according to the state of the said at least one component of the said communication medium; and,   storing in memory the said conditions for activation of the said at least one alarm and an identification of the said at least one alarm.       

     In this way the method according to the invention makes it possible to do away with the combinatorial analysis of breakdown configurations for the communication medium and to express the effects of breakdowns of the communication medium from a functional standpoint. The use of a unique form of representation makes it possible to simplify the specification and implementation of the associated logic. 
     The fact of not defining alarms for each of the states of the communication medium but adding to the logic already defined by the operational systems a logic taking these states into account makes it possible to limit the design effort for the alarms by focusing on the operational effects and not on the architectural implementation methods, while not impairing the level of false alarms. Moreover, since wording-type changes in the alarms by the operational systems do not impact the activation logic, the industrial process of keeping the alarms up to date is simplified. 
     The invention also has as an object a method for monitoring at least one avionic system connected to a communication medium comprising at least one component, this method comprising the following steps,
         determining the state of the said at least one component of the said communication medium;   evaluating an indicator of state of the said communication medium from the said state of the said at least one component of the said communication medium and from a formal predetermined modeling of the communication flows of the said communication medium; and,   selecting and activating an alarm according to the said evaluated state of the said communication medium and according to a predetermined modeling of the consequences of the said evaluated state of the said communication medium on the functioning of the said at least one avionic system.       

     In this way the method according to the invention makes it possible to do away with the combinatorial analysis of breakdown configurations for the communication medium and to simplify the analysis of the effects of breakdowns of the communication medium. 
     The said determination of the state of the said at least one component of the said communication medium advantageously is accomplished with the aid of communication means independent of the said communication medium in order to improve the overall reliability and limit disruptions of the communication medium. 
     According to a specific embodiment, the said step of selecting an alarm comprises the following steps, 
     Determining a breakdown of the said at least one component of the said communication medium; and,
         if the said breakdown of the said at least one component of the said communication medium has an impact on the functioning of the said at least one avionic system: selecting and activating an alarm linked to the said impact on the function of the said at least one avionic system.       

     In this way the method according to the invention makes it possible to simplify analysis of the consequences of breakdowns of the communication medium on the avionic systems. 
     Again according to a specific embodiment, if the said breakdown of the said at least one component of the said communication medium has no impact on the functioning of the said at least one avionic system and if the said breakdown affects communication between the said at least one avionic system and the means implementing the said monitoring method, the said method further comprises steps of selecting and activating an alert indicating that the said at least one avionic system no longer is being monitored. 
     In this way the invention makes it possible to distinguish the breakdowns having a direct impact on the avionic systems from the other breakdowns. 
     Again, according to a specific embodiment, the method further comprising the following steps,
         receiving an indication relating to the functioning of monitoring means, the said monitoring means implementing a method similar to the said monitoring method; and,   evaluating the monitoring of the said at least one avionic system according to the said indication relating to the functioning of the said monitoring means and to the said indicator of state of the said communication medium.       

     In this way, analysis of the possible impairment of the monitoring performance makes it possible to direct the operator to alternative means according to the criticality of the operational function if necessary. 
     The method advantageously further comprises a step of confirming the said indicator of state of the said communication medium. According to a specific embodiment, the said confirming step is based on at least one information item received from the said at least one avionic system. 
     In this way the invention makes it possible to favor the positive information items considering that an operational system is able to determine its functional state and that the perceived state of the communication medium may be erroneous. 
     Each of the said alarms advantageously is defined by a logic specific to the said at least one avionic system to which the said indicator of state of the said communication medium is contributing if this is relevant for simplifying implementation. 
     The invention also has as an object a device in an aircraft comprising means adapted for the implementation of each of the steps of the method described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages, purposes and characteristics of this invention become apparent from the detailed description that follows, presented by way of non-limitative example, with reference to the attached drawings in which: 
         FIG. 1 , consisting of  FIGS. 1   a  and  1   b , schematically shows a communication medium as well as means for observation of the active components of this medium, respectively; 
         FIG. 2  shows an example of implementation of a logic circuit that can be used for activation of an alert by an equipment item of the monitoring system; 
         FIG. 3  presents an example of implementation of the invention for monitoring an operational system of LGERS type (Landing Gear Extension and Retraction System); 
         FIG. 4 , consisting of  FIGS. 4   a  and  4   b , illustrates an example of the algorithm used to implement the invention; and, 
         FIG. 5  shows an exemplary apparatus making it possible to implement the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention relates to a centralized monitoring system enabling the diagnosis of the monitored operational systems and of the functions performed by these systems as well as the development and display of alarms enabling an operator to handle the impaired situations resulting from impairments of these functions. 
     Redundancy of the centralized monitoring system preferably is implemented by means of functions independent of each other. The method for monitoring of the shared communication medium advantageously takes this independence into account, while ensuring coherence in the performance of these independent functions. 
     The architecture of the monitored operational systems comprises a communication medium shared among the different monitored operational systems made up in particular of one or more active components such as switches. It should be noted here that if the number of switches is high, the number of combinations representing possible breakdown configurations is substantial and that, for reasons of cost, it is hard to envisage an exhaustive detailed analysis. 
     The handling of the detected breakdowns varies according to the nature of the breakdowns. For example, only the operational functions performed by the monitored systems require the development of an information item in the event of impairment. As a matter of fact, the impairment of the communication medium function itself is not, a priori, an information item relevant for conducting the flight. Only an information item linked to the impact of this impairment on the operational user functions of the communication medium is relevant. 
     Monitoring of the systems and associated operational functions advantageously is performed through the communication medium used to perform the operational functions. 
     Implementation of the invention comprises two phases:
         a preliminary analysis phase making it possible to model the data flows and the effects of breakdowns of the operational systems and of the disruptions in data flows; and,   a monitoring phase based on the modeling done during the preliminary phase.       

       FIG. 1   a  illustrates a shared communication medium in the form of communication network  100  made up of five nodes  105 - 1  to  105 - 5  as well as links between these nodes and between these nodes and the avionic systems and the monitoring systems. Each node here comprises two redundant components. For example, node  105 - 2  comprises redundant components  110 - 2 - 1  and  110 - 2 - 2 . The components preferably are connected with each other so as to form two redundant and independent local networks, in such a way that the breakdown of one or more components of a local network does not affect communications among the systems connected to the communication network. For example, component  110 - 1 - 1  is connected to component  110 - 2 - 1  and component  110 - 1 - 2  is connected to component  110 - 2 - 2  while component  110 - 1 - 1  is not connected to component  110 - 2 - 2  and component  110 - 1 - 2  is not connected to component  110 - 2 - 1 . 
     Access to the shared communication medium is achieved through a node  105 - i.    
     The data flows in the communication network, that is, the paths taken through the network, here are determined in static manner in order to avoid a reconfiguration of the communication paths in the event of breakdown. 
     According to the example shown, three operational systems  115 - 1  to  115 - 3  are connected to the communication network. For reasons of clarity, each operational system here is composed of a sole equipment item. 
     The centralized monitoring system comprises two redundant equipment items  120 - 1  and  120 - 2 . Each of the components  120 - 1  and  120 - 2  has a functioning independent of the functioning of the redundant component. In particular, the alert display devices are different. As soon as one of the equipment items of the monitoring system detects a condition or a set of conditions that requires display of an alert, it activates the display thereof without synchronization or verification with the redundant equipment item of the monitoring system. It should be noted that the topology of the communication network illustrated on  FIG. 1   a  is provided only by way of example. 
     The state of the communication medium is analyzed by the two equipment items  120 - 1  and  120 - 2  of the centralized monitoring system. 
     According to a specific embodiment illustrated on  FIG. 1   b , each equipment item of the centralized monitoring system receives an indicator of state of each communication node  105 - i , for example a Boolean value, by means of a wired state indicator  112 , that is, with the aid of a specific link between each equipment item of the monitoring system and each node of the shared communication medium, different from the shared medium. By way of illustration, the state of each node can assume one of the following values:
         OK if the state indicator signals a normal functioning; and,   KO if the state indicator signals a breakdown.       

     By using these states, the notation  110 - i - j _OK can be used, for example, if the component j of node  105 - i  is functioning correctly. Conversely, if component  110 - i - j  is not functioning correctly, the notation  110 - i - j _KO can be used. 
     As indicated above, the communication flows between operational systems, identified by the paths taken through the communication medium, preferably are predetermined. Each path can be identified by the list of nodes traversed. Thus, for example, the communication flow between operational systems  115 - 1  and  115 - 2  through nodes  105 - 1  and  105 - 2  can be marked PATH( 105 - 1 ,  105 - 2 ). Likewise, the communication flow between operational system  115 - 3  and the communication medium though node  105 - 5  can be marked PATH( 105 - 5 ). 
     Each equipment item of the centralized monitoring system determines the state of the communication function from the state of each of the components making up the nodes traversed by a flow. A communication path is considered to be lost if the breakdown configuration of the components making up the path is such that the two redundant local networks are affected. 
     In considering, for example, the communication flow between operational systems  115 - 1  and  115 - 2 , marked PATH( 105 - 1 ,  105 - 2 ), the path PATH( 105 - 1 ,  105 - 2 ) can be operational PATH( 105 - 1 ,  105 - 2 )_OK or broken down PATH( 105 - 1 ,  105 - 2 )_KO. The state of the communication flow PATH( 105 - 1 ,  105 - 2 ) thus can be determined by the following relationships,
 
PATH(105-1,105-2)_KO=(110-1-1_KO OR 110-2-1_KO) AND (110-1-2_KO OR 110-2-2_KO)
 
where ‘AND’ and ‘OR’ represent an ‘and logic’ and an ‘or logic,’ respectively.
 
     For each operational system and for each alert associated with this system, the breakdown condition or conditions of the system and of the communication medium are determined. These conditions can be determined by functional analysis and grouped in a table. 
     Let us consider an example according to which a functional analysis of operational system  115 - 1 , independent of the structure of the communication network, shows that an alert of type  115 - 1 _Alert-Fn 1  is to be activated if internal function Fn 1  is not available or cannot be executed (for example if a portion of this function is executed by operational system  115 - 2  and this operational system  115 - 2  is broken down or is not accessible). 
     In this way, it is possible to infer therefrom that the alert of type  115 - 1 _Alert-En 1  is to be activated under the following conditions,
         operational system  115 - 1  indicates to equipment items  120 - 1  and/or  120 - 2  of the monitoring system, a breakdown of the Fn 1  function, with the aid, for example, of the message  115 - 1 -Error-Fn 1 ;   equipment items  120 - 1  and/or  120 - 2  of the monitoring system do not receive any message from operational system  115 - 1  although no breakdown is detected in the communication medium between component  115 - 1  and equipment items  120 - 1  and  120 - 2  of the monitoring system;   the communication flow between operational system  115 - 1  and the communication medium is disrupted; or,   the communication flow between operational systems  115 - 1  and  115 - 2  is disrupted.       

     It should be noted that these conditions are easily verified by the monitoring system. In particular, the first condition is detected by the equipment items of the centralized monitoring system by the receipt of the message  115 - 1 -Error-Fn 1  through the communication network. 
     The second condition is detected by the equipment items of the centralized monitoring system by the absence of receipt of a state message originating from operational system  115 - 1 . Each equipment item of the centralized monitoring system ascertains that this loss is not due to a breakdown of the communication medium by verifying that the communication path between operational system  115 - 1  and itself is not broken. 
     If communication between an operational system and an equipment item of the centralized monitoring system is available, alerts linked to this operational system advantageously are activated on the basis of the monitoring information items received from the monitored operational system. As a matter of fact, although monitoring of the communication medium is simple and robust, a theoretical loss of communication flow can be detected erroneously. 
     To this end, the equipment items of the centralized monitoring system advantageously develop a communication flow validity information item based on the actual receipt or non-receipt of the information items and not on the observation of the state of the communication medium. In this way, the failure of a communication flow is considered as such only in the absence of receipt of messages from the corresponding operational system. 
     For example, the information item determined by equipment item  120 - 1  of the monitoring system according to which one of the paths PATH( 105 - 1 ), PATH( 105 - 1 ,  105 - 2 ) or PATH( 105 - 1 ,  105 - 3 ) is not valid, is to be confirmed, for example by the absence of receipt of messages from operational system  115 - 1 . 
     For each of the alerts defined in the centralized monitoring system, the activation logic for these alerts takes into account the conditions for activation. 
       FIG. 2  shows an example of implementation of a logic circuit  200  that can be used for activation of alert  115 - 1 _Alert-Fn 1  by equipment item  120 - 1  of the monitoring system. As illustrated by OR  205 , alert  115 - 1 _Alert-Fn 1  is activated only if one or the other of the two following conditions is met,
         equipment item  120 - 1  of the monitoring system has received a message  115 - 1 -Error-Fn 1  corresponding to alert  115 - 1 _Alert-Fn 1  from operational system  115 - 1 ; or,   the validated state combination for paths PATH( 105 - 1 ), PATH( 105 - 1 ,  105 - 2 ) and PATH( 105 - 1 ,  105 - 3 ) is such that equipment item  120 - 1  of the monitoring system is unable to exchange data with operational system  115 - 1 .       

     The state combination for paths PATH( 105 - 1 ), PATH( 105 - 1 ,  105 - 2 ) and PATH( 105 - 1 ,  105 - 3 ) consists here in performing the following operations,
         determining the OR  210  between the values of PATH( 105 - 1 ) and PATH( 105 - 1 ,  105 - 2 ) and reversing the result in reverser  215 ;   determining the AND  220  between the value obtained at the output of reverser  215  and the value of PATH( 105 - 1 ,  105 - 3 ) and reversing the result in reverser  225 ; and   determining the AND  230  between the value obtained at the output of reverser  225  and the value of validation condition  115 - 1 _Invalid (the value of  115 - 1 _Invalid is FALSE if a message is received from operational system  115 - 1  by equipment item  120 - 1  of the monitoring system, otherwise it is TRUE.       

     As illustrated on  FIG. 3 , the invention can be implemented, for example, to control an operational system LGERS 3  (Landing Gear Extension and Retraction System) referenced  315 - 1 , connected to a node  305 - 7  of a network comprising switches  310 - 7 - 1  and  310 - 7 - 2 . Breakdown conditions are, for example, the following,
         LGERS 3   315 - 1  declares itself broken down (Boolean variable LGERS 3 _FAULT);   LGERS 3   315 - 1  loses its connection to the network (loss of the node comprising switches  310 - 7 - 1  and  310 - 7 - 2 ); or,   LGERS 3   315 - 1  loses communication with operational system SEPDC 1  (Supplementary Electrical Power Distribution Center  1 ), referenced  315 - 2 , connected to a node  305 - 5  of the network comprising switches  310 - 5 - 1  and  310 - 5 - 2 . The loss of communication is expressed by the loss of path PATH( 305 - 5 ,  305 - 7 ).       

     It should be noted here that the third condition is included in the second. 
     The thick unbroken-line arrow represents transmission of the LGERS 3   315 - 1  status indicator to FWS 1   320 - 1  while the thick dotted-line arrow represents communication between LGERS 3   315 - 1  and SEPDC 1   315 - 2 . 
     The first condition is detected by FWS 1  (Flight Warning System  1 ), referenced  320 - 1  by receipt through the communication medium of the value of the Boolean variable LGERS 3 _FAULT transmitted by operational system LGERS 3   315 - 1 . The second condition is characterized by the loss of the two components of node  305 - 7 , that is, here switches  310 - 7 - 1  and  310 - 7 - 2 . The third condition is characterized by the loss of communication path PATH( 305 - 5 ,  305 - 7 ). 
     If a breakdown occurs in switches  310 - 3 - 1  and  310 - 7 - 2 , operational system FWS 1   320 - 1  loses communication with operational system LGERS 3   315 - 1 . The operational system LGERS 3   315 - 1  breakdown alert, however, is inhibited because the loss of path PATH( 305 - 3 ,  305 - 7 ) is not a breakdown condition of the LGERS 3   315 - 1  function. 
     Likewise, if a breakdown occurs in switches  310 - 3 - 1 ,  310 - 7 - 2  and  310 - 5 - 1 , operational system FWS 1   320 - 1  loses communication with operational system LGERS 3   315 - 1 . In this case, operational system FWS 1   320 - 1  activates an LGERS 3   315 - 1  alert because the detection of a loss of path PATH( 305 - 5 ,  305 - 7 ), here due to a breakdown of switches  310 - 5 - 1  and  310 - 7 - 2 , is a breakdown condition of operational system LGERS 3   315 - 1 . 
     Finally, if a breakdown occurs in switches  310 - 5 - 1  and  310 - 7 - 2 , operational system FWS 1   320 - 1  still receives the LGERS 3   315 - 1  state message and an alert concerning operational system LGERS 3   315 - 1  is activated only if this state message signals a problem on the LGERS 3   315 - 1  function. 
       FIG. 4 , consisting of  FIGS. 4   a  and  4   b , illustrates an example of an algorithm used to implement the invention.  FIG. 4   a  shows the portion of the algorithm used during the preliminary analysis phase while  FIG. 4   b  shows the portion of the algorithm used to monitor the shared communication medium. 
     As illustrated on  FIG. 4   a , after the communication flows in the shared communication medium have been determined (step  400 ), a functional study of the shared communication medium is conducted (step  405 ). Indexes i and j are initialized at zero (step  410 ). The value i here represents the index of the selected operational system whereas the value j represents the index of the selected alarm of the operational system i. 
     The conditions of alarm j of operational system i then are determined according to the breakdown conditions for alarm j of operational system i and according to the functional analysis of the communication medium performed (step  415 ). To this end, the conditions under which the breakdown of one or more components of the communication medium is to activate alarm j of operational system i are determined. The set of conditions determined in this way here is stored in memory in a table  420 . 
     Index j then is incremented by one (step  425 ) and a test is performed to determine whether index j is equal to the number of alarms of operational system i (step  430 ). If index j is not equal to the number of alarms of operational system i, the two preceding steps ( 415  and  425 ) are repeated. 
     If index j is equal to the number of alarms of operational system i, index j is reinitialized to zero and index i is incremented by one (step  435 ). A test then is performed to determine whether index i is equal to the number of operational systems to be monitored (step  440 ). If index i is not equal to the number of operational systems to be monitored, steps  415  to  440  are repeated. If on the contrary index i is equal to the number of operational systems to be monitored, the preliminary phase is terminated, that is, the conditions for activation of the alarms of the operational systems to be monitored have been determined. 
       FIG. 4   b  illustrates an example of the algorithm used to monitor a communication medium and operational systems in order to activate one or more alarms if necessary. 
     The messages transmitted by the operational systems to signal a breakdown are received by the monitoring system (step  450 ) if the state of the communication medium so permits. Simultaneously, before or afterwards, the monitoring system determines the status of the communication medium from, for example, the node state indicators as described above (step  455 ). 
     These information items are used to establish an overall status of the monitored system (step  460 ), that is, of the operational systems and of the communication medium. This status then is compared with the conditions for activation of alarms stored in memory, for example in table  420  (step  465 ). If these conditions for activation of one or more alarms are met, the corresponding alarm or alarms are activated (step  470 ). Steps  450  to  470  then are repeated to monitor the system continuously. 
       FIG. 5  illustrates an example of apparatus  500 , such as a microcomputer, adapted for implementing the invention. Apparatus  500  is an example of an equipment item of the monitoring system. 
     Apparatus  500  preferably comprises a communication bus  502  to which there are connected,
         a central processing unit  503  such as a microprocessor;   a read-only memory  504  or Read Only Memory (ROM), that can comprise one or more programs “Prog”;   a random-access memory  506  or Random Access Memory (RAM), comprising registers adapted for storing in memory variables and parameters created and modified during execution of the aforementioned programs; and   a communication interface  518  connected to a distributed communication network  520 , the interface being capable of transmitting and receiving data.       

     Apparatus  500  optionally can have one, several or all of the following devices:
         a screen  508  for displaying data and/or serving as a graphical interface with the user who will be able to interact with the programs according to the invention, with the aid of a keyboard  510  or any other means such as a pointing device, as, for example, a mouse  511  or a light pen, a touch-sensitive screen or a remote control;   a hard disk  512  that can comprise programs and/or data, in particular data processed or to be processed according to the invention;   a diskette reader  514  adapted for receiving a diskette  516  and for reading or writing therein data processed or to be processed according to the invention; and,   a memory card reader adapted for reading or writing data therein, in particular data processed or to be processed according to the invention.       

     The communication bus allows communication and interoperability among the different components included in apparatus  500  or connected thereto. The depiction of the bus is not limitative and, in particular, the central unit is capable of communicating instructions to any component of apparatus  500 , directly or through another component of apparatus  500 . 
     The executable code of the program or programs making it possible for apparatus  500  to implement the processes according to the invention can be stored, for example, in hard disk  512  or in read-only memory  504 . 
     According to one variant, diskette  516  can contain data as well as the executable code of the aforementioned programs which, once read by apparatus  500 , can be stored in hard disk  512 . 
     Alternatively, the executable code of the programs can be received through communication network  520 , via interface  518 , to be stored in a manner identical to that described above. 
     The diskettes can be replaced by any information medium such as, for example, a compact disk (CD-ROM) or a memory card. Generally speaking, an information storage means, readable by a computer or by a microprocessor, integrated or not into the apparatus, possibly removable, is suitable for storing in memory one or more programs the execution of which allows implementation of the method according to the invention. 
     More generally, the program or programs will be able to be loaded into one of the storage means of apparatus  500  before being executed. 
     Central unit  503  controls the execution of the instructions or portions of software code for the program or programs according to the invention, which instructions are stored in hard disk  512 , in read-only memory  540  or in the other aforementioned storage components. During boot-up, the program or programs stored in a non-volatile memory, for example hard disk  512  or read-only memory  504 , are transferred into random access memory  506  (RAM), which then contains the executable code of the program or programs according to the invention, as well as the registers for storing in memory the variables and parameters necessary for implementation of the invention. 
     It should be noted that the apparatus comprising the device according to the invention also can be a programmed apparatus. The instructions for the program or programs implementing the invention can, for example, be implemented in a programmable or specific integrated circuit (Application-Specific Integrated Circuit, ASIC). 
     Naturally, in order to satisfy specific needs, an individual competent in the area of the invention will be able to apply modifications in the foregoing description.