Patent Number: 
Section: claims

1. A device for system diagnosis of an aircraft comprising equipment, said device comprising:means for the monitoring of the equipment and means for emitting messages of observations (O1, O2, . . . , On) on a basis of effects produced by equipment of the system;means for the determination of a set of observations (Eobs) on a basis of the messages of observations (O1, O2, . . . , On) arising from the means for the monitoring, of a log of the messages of observations (O1, O2, . . . , On) and of a model representing a current state of the system, said means for the determination of a set of observations (Eobs) implementing temporal logic;means for the determination of indictments on a basis of observations (O′1, O′2, . . . , O′k) of the set of observations (Eobs) and of a behavioural model of the system, the indictments being logical relations between operating modes of equipment having produced effects;means for the determination of maintenance operations on the basis of the indictments; anda model explorer for computing logical relations (LR1, LR2, . . . , LRk) associated with the observations (O′1, O′2, . . . O′k) on a basis of the behavioural model of the system, the means for the determination of the indictments comprising means for the con'unction of the logical relations (LR1, LR2, . . . , LRk),wherein the con'unction of the logical relations (LR1, LR2, . . . , LRk) is carried out by means of a binary decision diagram and comprises:determination of a first binary decision diagram (BBD1, BBD2, . . . , BBDk) for each observation (O′1, O′2, . . . , O′k) of the set of observations (Eobs);computation of a second binary decision diagram (BDD′) by a conjunction operation on the first binary decision diagrams (BBD1, BBD2, . . . , BBDk); andcomputation of an indictment binary decision diagram by the development of the second binary decision diagram (BDD′). 2. The device for system diagnosis according to claim 1, wherein the means for the determination of the indictments comprises a model explorer allowing the direct exploration of the behavioural model of the system and the extraction of events in the form of sequences. 3. The device for system diagnosis according to claim 2, wherein the means for the determination of indictments is on board the aircraft, the determination of the indictments being performed during flight. 4. The device for system diagnosis according to claim 2, wherein the means for the determination of indictments is situated on the ground, the determination of the indictments being performed during the flight. 5. The device for system diagnosis according to claim 1, wherein a binary decision diagram comprises nodes, from which two branches sprout, and terminal leaves connected together by branches, each node representing a Boolean variable indicating the presence or the absence of an event, a branch being termed a terminal if it ends at a terminal leaf of value 0 or 1, or being termed intermediate if it ends at another node, a first branch representing the case where the event represented is absent, and a second branch representing the case where the event represented is present, the diagram comprising a single root node from which two branches, to which nodes or leaves are connected in cascade, sprout. 6. The device for system diagnosis according to claim 5, wherein the development of the second binary decision diagram (BDD′) is carried out by performing traversals of the second binary decision diagram (BDD′) from the root up to each of the terminal leaves of value 1, a traversal corresponding to a combination of events having given rise to the set of observations (Eobs). 7. The device for system diagnosis according to claim 1, wherein the determination of the logical relations (LR1, LR2, . . . , LRk) is carried out on the basis of a storage unit for associating a logical relation with each observation. 8. The device for system diagnosis according to claim 1, wherein the behavioural model comprises a component for each item of equipment of the system, a component of the behavioural model comprising at least:an input stream, an output stream, a state indicating the availability of the item of equipment and comprising:a fault mode, for indicating whether the component is defective or healthy and an operating mode for indicating whether the component is turned on, turned off or unavailable, and a logical relation between the input stream, the output stream and the state, and the output stream. 9. The device for system diagnosis according to claim 1, wherein the system under diagnosis comprises a plurality of processing units and is decomposed into various hierarchical levels grouping together these various processing units, a first hierarchical level being lower than a second level when the first level comprises component processing units of the processing units of the second level. 10. The device for system diagnosis according to claim 9, wherein the computation means of the device is implemented on two different hierarchical levels of the system comprising:a first level implementing means for the monitoring and means for the determination of a set of observations; anda second level, higher than the first level, implementing means for the determination of a set of observations on the basis of the sets of observations arising from the first level, means for the determination of indictments and means for the determination of the maintenance actions. 11. The device for system diagnosis according to claim 9, wherein the computation means of the device according to the invention is implemented on three different hierarchical levels of the system comprising:a first hierarchical level implementing means for the monitoring;a second level, higher than the first level, implementing means for the determination of a set of observations on the basis of the messages arising from the means for the monitoring of the first level and means for the determination of indictments; anda third level, higher than the second level, implementing means for the determination of a set of observations on the basis of the indictments arising from the second level, means for the determination of indictments and means for the determination of the maintenance actions. 12. The device for system diagnosis according to claim 11, wherein the first level groups together processing units of Shop Replaceable Unit type corresponding to electronic modules internal to an item of equipment and in that the second level corresponds to a maintenance application internal to the item of equipment.