MIL-STD-1629-RevA - Barringer and Associates, Inc.

MT1,-STD-1629A3.2 Functional approach. The functional approach is normallyused when hardware items cannot be uniquely identified or when systemcomplexity requires analysis from the initial indenture level downwardthrough succeeding indenture levels. The functional approach is normallyutilized in an initial indenture level down fashion (top+own approach);however, it can be initiated at any level of indenture and progress ineither direction. Each identified failure mode shall be assigned aseverity classification which will be utilized during design to establishpriorities for corrective actions.3.3 Failure mode severity classification. Severity classificationsare assigned to each failure mode and each item to provide a basis forestablishing corrective action priorities. First priority shall begiven to the elimination of the identified Category I (catastrophic) andCategory 11 (critical) (see General Requirements, 4.4.3) failure modes.Where the loss of input or output at a lower indenture level is criticalto the operational success of a higher indenture level, action shall betaken to eliminate or control the identified failure modes. When identifiedCategory I and Category II failure modes cannot be eliminated or controlledto levels acceptable to the procuring activity, alternative controls andrecommen~at~ons shall be presented to the procuring activity.4. Procedure. Each single item failure, as its effects areanalyzed, is to be considered the only failure in the system. Where asingle item failure is non-detectable, the analysis shall be extended todetermine the effects of a second failure, which in combination with thefirst undetectable failure, could result in a catastrophic or criticalfailure condition. Passive and multiple failures which may result incatastrophic or critical conditions shall also be identified. Whensafety, redundant, or back-up items exist, failure assumptions shall bebroadened to include the failure conditions which resulted in the needfor the safety, redundant, or back-up item. Design changes or specialcontrol measures shall be identified and defined for all catastrophic(Category I) and critical (Category 11) failure modes. All singlefailure points identified during the analyses shall be uniquely identifiedon the FMEA worksheets to maintain visibility of these failure modes.4.1 System definition. The first step in performing the FMEAis to define the system to be analyzed. Functional narratives shall bedeveloped for each mission, mission phase, and operational mode andinclude statements of primary and secondary mission objectives. Thenarratives shall include system and part descriptions for each missionphase and operational mode, expected mission times and equipment utilization,functions and uu~put of each item, and conditions which constitutesystem and part failure,4.1.1 Mission functions and operational modes. The systemdefinition shall include descriptions of each mission in terms of functionswhich identify the task to be performed and the functional mode ofTASK 10124 November 1980101-2