The certification of an aircraft system requires the prediction of the number of occurrences of critical failures during aircraft life. To keep this number to an acceptable level, the system is fault-tolerant. Also certain repair strategies are applied to maintain fault-tolerance over time. The paper provides the mapping of some textual certification requirements into a generic stochastic model, and it investigates certain elementary, non-trivial models including deferred repair and hidden failures. The first aim was to translate textual certification requirements into a stochastic model. The relevant figure turned out to be the expected number of failures, the time scale is the 'number of flight hours', and repairs are important. The points of time when repair is possible are the set of positive integers. This makes the continuous time process in-homogenous. So, standard tools for 'solving' Markov Processes cannot be applied. Analytic formulae for the expected number of system failures are provided for a number of important practical cases including the effect of deferred repair. These help to find optimal tolerance times. The definition of the stochastic experiment (Omega, A, P) and the process Zt has been stressed to allow for model validation. So, first the path were constructed and from this the conditional probabilities were computed. Hence, the Markov property is a result, not an assumption. 'Failure states' of different components turn out to be stochastically dependent in the Go-If case. So they cannot be handled by standard tools for fault trees. Future related work will look into the link with 'Markov phase processes'.


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    Title :

    On the impact of deferred repair on the expected number of system failures - A stochastic model


    Additional title:

    Über den Einfluss einer verzögerten Reparatur auf die erwartete Anzahl von Systemfehlern - ein stochastisches Modell


    Contributors:


    Publication date :

    2009


    Size :

    8 Seiten, 5 Bilder, 6 Quellen



    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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