Abstract:
The invention relates to a system for recommending maintenance of helicopter engines depending on the technical condition of the engine, the standard replacement of parts between engines, and the replacement of parts with different parts. The system comprises: a centralized database storing data relating to (i) working condition and working condition indicators, (ii) modifications of the engines, (iii) maintenance plans for the engines, (iv) causes of unscheduled events, (v) maintenance applied to the engines, and (vi) instantiated configurations; means for acquiring the working condition indicators and for updating the working condition data; means for identifying maintenance to be applied to the engines depending on the data; means for generating an alarm for identified maintenance to be performed; means for the digitally-signed updating of the applied maintenance and configuration data according to maintenance operations; and means for deactivating an alarm once the maintenance associated with the alarm is completed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application under 35 U.S.C. §371 of PCT Application No. PCT/EP2012/061754, filed Jun. 19, 2012, which claims priority to and the benefit of European Application No. 11305774.9 filed on Jun. 20, 2011, which are incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to helicopter engines, and more specifically to the maintenance thereof. 
     STATE OF THE ART 
     A helicopter engine is a so-called “critical” system, with a very high variability of its components, parts, and functional assemblies of parts. 
     First, like any mechanical system, each of the parts and of the functional assemblies of parts, or “modules”, is submitted to wearing, to fouling, to the aging of lubricants, etc. or more generally submitted to a modification of their characteristics which makes them drift from their desired behavior. In the case of a helicopter engine, technical constraints to ensure the safety of flights are such that both the number of maintenance operations and the maintenance frequency are high, and especially much higher than the number of maintenance operations and the maintenance frequency of airplane engines, for example. 
     Then, for a same engine definition, the working conditions are much more variable than for an airplane engine. While an airliner engine typically performs a line flight with 90% of its flight time in cruise mode with stable and constant parameters, a same class of helicopter engines may be used to perform missions with a great variety of stress: load slinging missions successively and repeatedly requiring a high power and carried out close to the ground, and thus to the dust and other aerosols, passenger transport missions with a significant cruise phase at a high altitude, sea rescue missions with significant times of exposure to saline fog, combat missions, with a most highly variable profile . . . . 
     Then, helicopter engine constructors carry out constant research on such systems to improve their performance. Thus, the constructor of a helicopter engine may prescribe up to hundreds of modifications for an engine, especially modifications of the characteristics of parts. For example, the number of prescriptions to modify Turbomeca&#39;s “ARRIEL” helicopter engines is now greater than 300, which amounts to a number of theoretically possible configurations greater than 2 300  for an engine of this class, although, among possible configurations, only given ones, define by strict rules of implication and/or exclusion between modifications, are allowed to navigate. Indeed, an engine is a highly-optimized system, due to its design constraints, substantially more than an airplane engine, for example. As an example, an “ARRIEL” engine delivers a 700 horsepower for a 109-kg weight, which result is obtained by optimizing in the extreme each part and each module with respect to one another. Thereby, even though the constructor may issue modification prescriptions, this does not mean that said modifications are necessarily implemented by the user of an engine. It can besides be observed that each engine has a configuration which is generally specific thereto and clearly different from the configuration of other engines of the same class. 
     Thus, a helicopter engine is a critical system, with highly-interdependent elements which may take a very high number of possible configurations, and submitted to a number of maintenance operations which is also high, which directly impact the engine performance and safety, at the very least disproportionately as compared with other types of commercial engines, including airliner engines. 
     A human maintenance operator cannot manage such a complexity with all the details to be integrated. Thus, the deployed maintenance concepts have level-1 and 2 maintenance operators work on a simplified and synthetic model of the engine working conditions and configuration: working conditions parameters are by a limited number (typically from two to three parameters) and the configuration management is limited to the first stages of the nomenclature by decreasing the number of modifications visible at level 1 and 2. To ensure the safety of flights whatever the engine operating conditions (which cannot be reflected in detail by the synthetic parameters), significant security margins are applied to the maintenance prescriptions. Thus, the maintenance of a helicopter engine is actually significantly sub-optimal, and further possibly non-constant since it essentially depends on the skill of the different maintenance operators working on the engine. 
     DISCUSSION OF THE INVENTION 
     The present invention aims at providing a maintenance prescription system which takes into account the complexity of the maintenance already applied, the in-flight operating conditions, and the specific engine configuration to determine maintenance operations for a helicopter engine. 
     For this purpose, the invention aims at a system for prescribing maintenance of helicopter engines belonging to the same engine class and formed by elements that vary over time depending on the technical condition thereof, the standard replacement of parts between engines, and the replacement of parts with different parts, comprising:
         a centralized database storing operational data relating to:
           working condition, describing the history of one or more working condition indicators of each of the engines,   possible modifications and authorized modifications of the engines;   the definition of maintenance plans for the engines according to predetermined values of the working condition indicator(s);   the description of the probable causes of unscheduled events according to the data relating to possible and authorized modifications and the working condition data;   maintenance applied, describing the nature and history of maintenance operations applied to each of the engines; and   instantiated configurations, describing the nature and the history of the configuration modifications applied to each of the engines; and   
           means for acquiring the working condition indicator(s) of each of the engines and for updating the working condition data depending on the acquired value of the indicator(s) of each engine;   means for identifying a maintenance operation to be applied to each of the engines depending on the operational data in the database;   means for generating a continuous alarm for each identified maintenance operation to be performed;   means for the digitally-signed updating of the applied maintenance data and the instantiated configuration data according to each maintenance operation applied to each of the engines; and   means for deactivating an activated alarm if at least the digitally-signed update of the data resulting from the identified applied maintenance operation associated with the alarm is carried out.       

     “Operational working condition data” means objective data describing the conditions to which the engines have been submitted in flight or on ground during their operation and based on which a decision is taken to service the engines. As an illustration, a piece of working condition data is the number of hours of flight of the helicopter, an overhaul of the helicopter engine being for example performed every 3,000 hours of flight. 
     “Operational data relating to possible engine modifications” designate data describing all the modifications, or configurations, which are possible on engines belonging to a same class. 
     “Operational data relating to authorized engine modifications” designate data describing all the authorized or “navigable” configurations from among the possible configurations of engines belonging to a same class. 
     “Operational maintenance plan definition data” designates data describing all maintenances which are predictably triggered for an engine of a same class, independently from their specific configurations, based on the value of the working condition indicator(s) of the engines. 
     “Operational data of description of the probable causes of unscheduled events” designates data describing probable causes, preferably with associated probabilities, of unscheduled events occurring on the engines, especially failures. 
     “Maintenance operation” here designates an action taken on an engine, of whatever nature. Maintenance operations gather actions of engine failure assistance and repair, setting, overhaul, control, and checking. 
     “Operational data relating to maintenance applied” here designates data describing all the maintenance operations implemented on the engines. 
     “Operational data relating to instantiated configurations” here designates the data describing the specific configurations of engines following configuration modifications after, for example, modification prescriptions by the constructor. 
     First, the system according to the invention plots all the data of all the engines belonging to a same class, which allows a specific follow-up of each engine. 
     Further, all the data associated with a specific engine form an “Electronic Engine Logbook” which contains the history of all the maintenance operations applied to the engine, the working condition operational data, as well as the specific configuration thereof, and replaces the handwritten engine logbook. The analysis of the flight indicator(s), as well as the maintenance prescriptions, are thus performed based on these data, which contain the history of all the maintenance operations applied to the engine, the in-flight or ground operating conditions as well as the history of all configurations, which thus enables to take into account the complexity of the maintenance of a helicopter engine. Further, the history of the data also enables to implement tendency analyses, and thus to correct and/or to improve, particularly, the data of definition of the maintenance plan and of definition of the causes of unscheduled events. 
     Then, the system implements an alarm activation/deactivation system. An alarm is activated at least for each maintenance operation to be immediately performed on an engine. The use of alarms aims not only at warning the maintenance operator that a maintenance operation should be performed on an engine, but above all at forcing the operator to update the database, which ascertains that the data in the base are always complete and relevant. More specifically, the system according to the invention plays the role of paper maintenance logbooks, which forces maintenance operators to necessarily use the system and thus to update it. The combination of the technical alarm management and of the legal obligation of use of the system thus provides the technical effect of a complete database. 
     According to a variation of the system, the alarm also blocks any action on the system relative to engines for which an alarm has been activated, as long as the corresponding procedures of deactivation by updating of the data have not been carried out. 
     The invention also aims at a method of prescribing maintenance of helicopter engines belonging to the same engine class and formed by elements that vary over time depending on the technical condition thereof, the standard replacement of parts between engines, and the replacement of parts with different parts, comprising:
         storing operational data relating to:
           working condition, describing the history of one or more working condition indicators of each of the engines,   possible modifications and authorized modifications of the engines;   the definition of maintenance plans for the engines according to predetermined values of the working condition indicator(s);   the description of the probable causes of unscheduled events according to the data relating to possible and authorized modifications and the working condition data;   maintenance applied, describing the nature and history of maintenance operations applied to each of the engines; and   instantiated configurations, describing the nature and the history of the configuration modifications applied to each of the engines; and   
           acquiring the working condition indicator(s) of each of the engines and updating the working condition data depending on the acquired value of the indicator(s) of each engine;   identifying a maintenance operation to be applied to each of the engines depending on the operational data in the database;   generating a continuous alarm for each identified maintenance operation to be performed;   updating with a digital signature the applied maintenance data and the instantiated configuration data according to each maintenance operation applied to each of the engines; and   deactivating an activated alarm if at least the digitally-signed update of the data resulting from the identified applied maintenance operation associated with the alarm is carried out.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be better understood on reading of the following description provided as an example only in relation with the accompanying drawings, where: 
         FIG. 1  is a simplified view of a maintenance prescription system according to the invention; 
         FIG. 2  is a plot of a first indicator of the working condition over time stored in the database of the system according to the invention; 
         FIGS. 3 and 4  respectively are plots of a second working condition indicator stored in the database and of its time drift; and 
         FIGS. 5 and 6  are examples of a probability tree used for the identification of probable failure causes. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , a maintenance prescription system according to the invention is illustrated under general reference numeral  10 . System  10  comprises a central server  12  implementing a database  14  gathering data relative to engines of a helicopter fleet  16 , a software unit  18  managing the access to server  12  and the safety thereof, and software units  20  for processing the data contained in base  14 . 
     Database  14  gathers all the data of the engines in the fleet allowing a continuous follow-up of the navigability of these engines, and thus allowing to prescribe maintenance operations thereon, particularly according to their specific configurations and to the history of the operations applied thereto. 
     The access to central server  12  is performed by any computer means  22  available for users, office computers, laptop computers, tablets, “smartphones”, or others, via one or several telecommunication networks  24 , for example, the Internet, local networks, virtual private networks, etc. As opposed to central server  12 , computer means  22  available for a user are called “local station”. 
     Preferably, a local station  22  comprises a software unit implementing, with access and security management unit  18 , a software architecture of web client/server type, thus allowing a connection with central server  12  via a single web portal for all users. 
     The connection to central server  12  is performed by authentication, the user desiring to connect to central server  12  having an account thereon, to which it accesses by keying in at least a login and a password. 
     Access management and security unit  18  further implements functions of security and confidentiality of the connections with server  12 , particularly antivirus, anti-intrusion, anti-aspiration, abnormal traffic inspection, and other functions, and traces each connection and each action performed via central server  12  on database  14 . Further, each user account is associated with specific privileges according to the user&#39;s nature (maintenance operator, engine owner/lessor organization, engine constructor, etc.), these privileges defining the type of action that the user can undertake on database  14  and the type of data in base  14  to which the user has access. 
     Different authentication levels may further be implemented according to a user&#39;s privileges. Advantageously, for privileges bearing on a modification of the data of base  14 , a strong authentication based on a digital or electronic signature is required. 
     Database  14  particularly comprises operational data relating to:
         the working condition, describing the history of one or several indications of the working condition of each of the engines, such as for example, the number of hours of flight or the number of cycles of each of the engines. The number of cycles is an indicator describing the number of times that the speed of an engine integrally describes a given speed range during a flight. A working condition indicator may also comprise flight conditions of a helicopter impacting the working condition of an engine, such as for example a flight in a sandy, salty, or other environment;   possible modifications and authorized modifications of the engines. Advantageously, database  14  comprises not only the authorized, or “navigable”, engine modifications, but also all possible engine modifications. The authorized configurations can be deduced from the strict rules of implication and/or exclusion. This enables to compare a specific engine configuration, which may be a possible but non-authorized configuration, for example, due to a maintenance error, with authorized configurations. Configuration modification errors can thus be detected;   the definition of maintenance plans for the engines according to predetermined values of the working condition indicator(s). For example, this concerns maintenance operations to be applied every X hours of flight of the engines, or when the number of cycles of an engine exceeds a predetermined threshold value, or when an engine has been flown in a specific environment, etc.;   the description of the probable causes of unscheduled events, and especially of failures, according to the data relating to possible and authorized modifications and to the working condition data. Preferably, the description data are organized in the form of a probability tree according to the possible engine modifications, as will be explained in further detail hereafter:   maintenance applied, describing the nature and history of maintenance operations applied to each of the engines; and   instantiated configurations, describing the nature and the history of the configuration modifications applied to each of the engines.       

     Database  14  also comprises operational data describing the operation protocol of each maintenance operation, that is, what a maintenance operator should do to properly carry out the maintenance operation, for example, in the form of reference technical documentation. 
     Because maintenance plan definition data, the data defining probable causes, and operational data are capable of varying over time (updates, optimization of maintenance plans, of operating modes, improved identification of failure causes, etc.), database  14  comprises all versions of these data, and particularly all versions of the reference technical documentation, as well as the timestamping of said versions, that is, the period during which they were used in maintenance and configuration modification operations, to associate each applied operation and modification performed with a version of the data. 
     The database also comprises a set of time signatures characteristic of events, and especially of failures, with which are compared the working condition indicators stored in base  14 , especially to determine unscheduled events on the engines, and thus trigger a maintenance operation, as will be explained in further detail hereafter. 
     Software processing units  20  comprise a first unit  26  of electronic consultation of data from base  14  enabling to interactively display them in the form of maintenance manuals, or troubleshooting manuals, of spare parts catalogues, of tooling catalogues, of newsletters issued by the constructor, especially concerning changes of configuration or other, and this, for each family, or class, of engines managed by system  10 . The access to this documentation is managed by consultation unit  26 , preferably according to the privileges assigned to the users, to the instantiated configuration of the engines, or any other criterion of interest. 
     Software processing units  20  comprise a second unit  28  for processing data generated during a flight, commonly called “flight data”, unit  28  enabling to collect the engine working condition indicators, to process them and to incorporate them into database  14 . 
     More specifically, processing unit  28  comprises a first sub-unit for collecting working condition indicators. The indicators and other flight data are collected by central server  12  from different acquisition channels, and especially from flight recorders  30 , from manual input means  32 , for example, for engines which are not equipped with embarked recorders, and from other computer systems  34 , which for example collect said data first. The collection is preferably supervised by a user from his local workstation  22 , so that he can view them and, if need be, modify them, before their downloading onto central server  12 . 
     Unit  28  further comprises a second sub-unit for validating and saving the collected data. The second sub-unit verifies the consistency of the collected data before they are saved in base  14 . In particular, the second sub-unit verifies the conformity of the data format with one or several formats required for these data, verifies that the data are not corrupted during the transmission, for example, by means of a data exchange between central server  12  and local station  22  to verify the integrity of the collected data. In case of a lack of consistency of the data, an alarm signal is emitted for sub-unit  28 . 
     A sub-unit for pre-processing the collected data may also be provided, for example, to generate composite working condition indicators from the working condition indicator values downloaded into central server  12 . Further, the values of the indicators, which are a synthesis of the working condition of an engine, may be generated by calculation, for example, according to raw flight data continuously or regularly recorded during a flight. Optionally, the raw flight data may be directly downloaded into central server  12  and the pre-processing sub-unit implements the calculations generating the values of the indicators. 
     Software units  20  also comprise a third maintenance prescription unit  36  which is executed once new values of the indicators of the working condition of an engine have been recorded in database  14 , or independently from a new data collection, by order of an authorized user. Particularly, the last values of the engine working condition indicators are compared with predetermined values defined in the operational maintenance plan data, to determine whether a maintenance operation should be applied to the engine. Maintenance plans especially correspond to maintenance operations predictable according to the current value of the working condition indicators. For example, a maintenance operation is executed every X hours of flight. 
     However, since database  14  contains the history of the working condition indicators, the history of the configuration modifications, and the history of the maintenance operations applied to each engine, it is possible to implement more complex tests than a simple comparison of a value with a triggering threshold to determine whether a maintenance operation should or not be applied. In particular, an analysis of the tendency of working condition indicators may be implemented by unit  36  since the variation of said indicators over time is known, with the possibility of weighting or not such analyses with the instantiated engine configurations and/or the maintenance operations already applied thereto. 
     When a maintenance operation to be applied to an engine is identified, an alarm signal is emitted by third unit  36 . Further, third unit  36  identifies according to the instantiated engine configuration, and optionally according to the maintenance operations already applied thereto, the data describing the operation protocol to be implemented in order to carry out the identified maintenance operation, such data being made available to the maintenance operator in charge of said operation. 
     Third unit  36  is also configured to determine whether non-predictable events have occurred. Particularly, the working condition indicators stored in database  14  are compared with the base of time signatures characteristic of events triggering maintenance operations. It is for example known that some indicators adopt a limited variation of their value during a normal engine operation, as illustrated, for example, in  FIGS. 2 and 3  which illustrate abrupt changes of the value of a working condition indicator. A comparison of the time variation of these indicators with a variation profile considered as abnormal thus enables to determine that a maintenance operation is likely to have to be applied in addition to the predictable operations prescribed in maintenance plans. 
     When the comparison with the signature base is positive, an analysis is carried out by third unit  36  on the applied maintenance operational data and on the instantiated configuration data to find out whether a previous action on the engine can explain the abnormal variation of the concerned working condition indicator(s). For example, an abrupt increase of the indicator of  FIG. 2  can be explained by a change in the engine configuration, while abrupt variations of the indicator illustrated in  FIGS. 3 and 4  can be explained by two successive replacements of an engine module, that is, its generator, such information being stored and especially timestamped in base  14 . The probable causes identified by this analysis are listed and transmitted by third unit  36  to authorized users. Further, the time signatures may also be associated with identified failures. A maintenance operation is thus prescribed by third unit  36 . Simultaneously, said unit also emits an alarm signal. 
     It should be noted that the storage of the history of configuration changes, of the maintenances applied, and of the working condition indicators enables to perform analyses taking into account the complexity of a helicopter engine. Indeed, as previously described, a helicopter engine is a hypercritical system having its operation influenced by all the maintenance operations and working conditions that it has undergone. Particularly, the working condition of an engine does not only depend on the last maintenance operation applied or on the last configuration modification. Thus, a maintenance operation, or a configuration modification, coupled to an older operation, may cause an untimely event, which can only be detected by an analysis according to the histories stored in database  14 . 
     Further, in the case where the event detected by third unit  36  is a failure, or after the manual input of the data characteristic of a failure by a user, third unit  36  implements an algorithm of identification of the probable causes of the failure according to the maintenance operations applied, to the instantiated engine configuration, to the working condition indicators, and to the authorized configuration modifications. 
     Particularly, the data relating to possible failure causes in database  14  are organized in the form of a probability tree. Two simple examples of probability trees are illustrated in  FIGS. 4 and 5 ,  FIG. 4  illustrating probable causes of a loss of information from an engine torque sensor, and  FIG. 5  illustrating probable causes of an engine performance loss. The probability tree is examined particularly according to the instantiated engine configuration and browsed by means of a Bayesian-type algorithm. Third unit  36  transmits at the end of its analysis a list of probable causes of the failure, preferably with a probability associated with each of them, as well as an associated maintenance prescription. At the same time, third unit  36  transmits an alarm signal. It should be noted that the trees illustrated in  FIGS. 4 and 5  are very simple and that, in practice, the number of possible configurations being very large, the probability tree is also complex. 
     Finally, processing units  20  comprise a fourth alarm management unit  40  which receives alarm signals from the other units. Alarm management unit  40  keeps up to date a list of alarm signals associated with each alarm-generating event, as well as a list of actions to be taken on database  14  to deactivate the alarms. 
     Particularly, an alarm is deactivated when a maintenance operation has been performed by a maintenance operator and that he/she has downloaded, with a digital signature, the description and the timestamping of the maintenance operation or the change of configuration that he/she has performed. Preferably, in case of a failure, the alarm is deactivated when the operator also fills in, with a digital signature, the information relating to the failure that he/she has identified, which enables, by recompiling the data relative to possible failure causes, to refine said data. In a variation of the invention, unit  40  may also block any operation on the data of base  14  relative to an engine as long as the description of the maintenance operation or of the configuration change on the engine has not been downloaded.