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4.17 Elementary Method "Failure Mode Effect Analysis" (FMEA)  

  4.17 Elementarmethode "Failure Mode Effect Analysis" (FMEA)

Contents  
  • 1 Identification/Definition of the Method
  • 2 Brief Characteristic of the Method
  • 3 Limits of the Methods Application
  • 4 Specification of the Methods Allocation
  • 5 Interfaces
  • 6 Further Literature
  • 1 Identification/Definition of the Method

    /MIL-STD 1629A, 1980/ chap. 3, pp. 3-5; chap. 4, pp. 5-11; chap. 5, pp. 11, 101-105

    2 Brief Characteristic of the Method

    Objective and Purpose

    The Failure Mode Effect Analysis (FMEA) is a method used for the identification of potential error types in order to define its effect on the examined object (System, Segment, SW/HW Unit) and to classify the error types with regard to criticality or persistency. This is to prevent errors and thus weak points in the design which might result in a endangering or loss of the system/software and/or in an endangering of the persons connected with the system/software. The FMEA is also to furnish results for corrective measures, for the definition of test cases and for the determination of operating and application conditions of the system/software.

    Means of Representation

    Means to represent the FMEA are e. g.:

    Operational Sequence

    The basic principle is that both in the functional hierarchy and in the program logic defined success or error criteria are systematically (functionally and chronologically) queried: what happens if? This analysis and evaluation has to be realized for all operating phases and operating possibilities.

    The FMEA process consists of the following main steps:

    3 Limits of the Methods Application

    Within the scope of submodel PM, the application of FMEA is limited to projects with much restrictive planned data or high requirements; a general application of FMEA would not be appropriate, considering the required effort and costs in comparison with the achieved results.

    Within the scope of the submodels SD and QA the method FMEA is applied if the reliability requirements to the System/to functional units are high.

    4 Specification of the Methods Allocation

    No. Activity Description
    4.1 Project Management (PM) Method FMEA is means to realize catastrophe analysis and risk analysis; originally it was designed for the safety analysis of systems. Therefore, in order to apply FMEA in the PM a certain new orientation is required. In this connection the steps and techniques of the FMEA remain unchanged. Only the examined objects, the risks, and the effects must be transformed in order to meet PM requirements.

    The operational sequence of FMEA in submodel PM is as follows:

    1. Generation of a list of all factors influencing the planning
    2. Specification of type and probability of abnormal behavior for each factor (by applying statistical methods)
    3. Investigation of the effects on other factors (by applying methods of the operations research, as e. g. simulation)
    4. Investigation and classification of the effects on the entire planning
    5. Finding out possibilities to discover the abnormal behavior
    6. Finding out possibilities to compensate the abnormal behavior
    7. Finding out possibilities to prevent an abnormal behavior
    FMEA is applied for a prospective and a retrospective risk analysis.

    In a prospective risk analysis, analyses are made constantly of the current schedule, personnel, and resource situation in order to detect and prevent possible problems at an early stage.

    In a retrospective risk analysis, past problems are analyzed in order to get information that might help to prevent these problems in the future.

    4.1.1 PM1.5 - Generation of Preliminary Plan In PM1.5, method FMEA is applied for the prospective risk analysis; in this connection it completely covers the subproduct Project Plan.Risk Considerations.
    4.1.2 PM7 - Risk Management In PM7 - Risk Management, method FMEA is applied for a prospective risk analysis; method NPT - Network Planning Technique must be applied additionally. In this connection, FMEA is used to detect risks, NPT is used to calculate risks. Together these methods meet the product requirements of subactivity PM 7.
    4.1.3 PM8 - Project Control Within the scope of the project steering, method FMEA is applied both for a prospective and for a retrospective risk analysis. FMEA is completed by the BA which supports the selection of the possibilities defined in the above mentioned steps 5 to 7. Together these methods meet the requirements of subproduct Project Plan.Risk Considerations.
    4.2 SD1.3 - Definition of Criticality and Quality Requirements Method FMEA is applied to define and explain the criticality levels of the system functions.

    By applying FMEA the subproduct User Requirements.Criticality of the System is completely covered.

    4.3 SD3.4 - Definition of Requirements for the Quality of the SW/HS Unit The decomposition of the total functionality of the system into segments and/or SW Units will be described.

    Method FMEA is applied to define and explain the criticality levels of the functions of the SW/HW Unit.

    By applying FMEA the subproduct 5.x.4.1.Technical Requirements.Criticality is completely covered.

    4.4 QA2.3 - Definition of Test Cases In the case where the reliability requirements are high, method FMEA is applied to define test cases for the following objects to be assessed:
    • SW/HW Unit
    • Segment
    • System
    Apart from the functional aspects on the Segment and system level, environmental aspects have to be taken into consideration as well.

    Subproduct Assessment Specification.Test Case Description is only completely covered by the additional application of method BBTD - Black Box Test Case Design.

    5 Interfaces

    - not applicable -

    6 Literature

    /Deutsch, 1988/ Software Quality Engineering
    /Leveson, 1986/ Software Safety: What, Why and How
    /MIL-STD 1629A, 1980/ Procedures for Performing a Failure Mode, Effects and Critically Analysis

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