MIL-STD-1629-RevA - Barringer and Associates, Inc.
MIL-STD-1629-RevA - Barringer and Associates, Inc. MIL-STD-1629-RevA - Barringer and Associates, Inc.
-.MIL-STD-1629A//:150.1.3 Intended use. The FMECA is potentially one of the mostbeneficial and productive tasks in a well structu~d reliability program.Since individual failure modes are lfsted in an orderly, organized fashion andevaluated, the FMECA serves to verify desfgn integrity, identify and quantifysources of undesirable failure modes, and document the reliability risks.FMECA results can be used to provfde the rationale for changes fn operatfngprocedures for ameliorating the effects or for detecting the incipience of theundesirable failure modes. Although the FMECAfs unessential reliabilitytask, it supplements and supports other engineering tasks throughidentification of areas in which effort should be concentrated. The FMECAresults are not only used to provide design guidance, but they are usedadvantageously in and for maintenance plannfng analys~s, logfstics supportanalysis, survivability and vulnerability assessments, safety and hazardsanalyses, and for fault detectfon and isolation design. This coincident useof the FMECA must be considered in FMECA planning and every endeavor nade toprevent duplication of effort by the program elements which utilfze FMECAresults.50.2 I%IEA (Task 101). The FMEA is an essential design evaluationprocedure which should not be Iimfted to the phase traditionally thought of asthe design phase. The initial FMEA should be done early fn the conceptualphase when desiqn criteria, missfon requirements, and conceptual desiqns arebeing developed”to evaluate the desiaqnapproach and to compare the beneffts ofcompeting design configurations. The FMEA will provide quick visibility ofthe more obvious failure modes and identffy potential single failure points,some of which can be eliminated with minfmal design effort. As the missfonand design definitions become more refined, the FMEA can be expanded tosuccessively more detafled levels. When changes are made in system design toremove or reduce the impact of the identified failure modes, the FMEA must berepeated for the redesigned portions to ensure that all predictable failuremodes in the new design are considered.50.3 CA (Task 102). The CA fs a procedure for associating failureprobabilities with each failure mode. Since the CA supplements the FMEA andis dependent upon information developed in that analysis, it should not beimposed wfthout imposition of the FMEA. The CA is probably most valuable formaintenance and logistics support orfented analyses since failure modes whfchhave a high probability of occurrence (high criticality numbers) requirefnvestfgatfon to identify changes whfch will reduce the potential impact onthe maintenance and logfstic support requirements for the system. Since thecriticality numbers are established based upon subjective judgments, theyshould only be used as indicators of relative priorities.50.4 FMECA+naintainability information (Task 103). This analysis is anextensfon 0$ h A and IS dependent up~ generated fnfonnation;therefore, the ‘~ECA-maintainability information analyses should not befmosed without imposition of the FMEA. The identification of how eachfa!Iurewfll be detected and localized will provide information for evaluatingItem testability. The failure mode listing whfch is included on the completedworksheet should be utilized to provide this required data for logistlcssupport analyses (LSA), maintenance plan analysis (MPA), and reliabilitycente~d maintenance (RCPI).A-3
—MIL-STD-1629A50.5 DMEA (Task 104). The DMEA provides essential inputs for thevulnerability assessment of a weapon system to aid in the identification ofdeficiencies-and the evaluation of des_ignsfor enhancing survivability. Sincethe DMEA utilizes the failure mode information from the FMEA, it should not beimposed without imposition of the FMEA. The DMEA, like the initial FMEA,should he done early in the conceptual phase to provide data related to thecapability of the conceptual weapon system design to survive the effects ofthe specified hostile threats. Development of this data before weapon systemdesiqn configuration is finalized will provide significant survivabilitybenefits with minimal impact on cost and schedule.50.6 FMECA plan (Task 105). The FMECA plan provides the contractor’splans and activities for implementing the FMECA tasks. The plan is used bythe procuring activity to evaluate the planned FMECA task efforts, and whenapproved, is used for monitoring contractor Implementation of the tasks. Theplan can be required as a separate document submittal or it can be included aspart of the Reliability Program Plan. The FMECA plan includes a descriptionof the contractor’s procedures for implementing the tasks and provides a crossindex showing the relationship of coincident performance and use of the FPEAtasks to preclude duplication of ef[ort. Sample contractor formats used inperformance of each FMECA task are Included as a part of each task specifiedin the contract statement of work.50.7 Criticality number (Cr) calculation example. Calculation ofmeaningful criticality numbers requires the use of specific failure rate andpart configuration data. When part configurations are known, failure ratedata can be obtained from the appropriate reliability prediction, field datafrom past systems of similar design and environmental use, or failure ratedata sources such as MIL-I{DBK-217. With known failure rates, the criticalitynumber for an item is the number of failures of a specific type expected permillion hours due to the item’s failure modes under a particular severityclassification as discussed in Task 101. A failure mode criticality number,Cm, for a particular severity classification is given by the expression:cm= f3aApt(1)The item criticality number, C , under ais then calculated by summing [he Cm forclassification. This sunwnation is givenparticular severity classification,each failure mode under that severityby the expressions:Cr = Z (Cm)nn=lOr(2)7 June 1983A-4
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—<strong>MIL</strong>-<strong>STD</strong>-<strong>1629</strong>A50.5 DMEA (Task 104). The DMEA provides essential inputs for thevulnerability assessment of a weapon system to aid in the identification ofdeficiencies-<strong>and</strong> the evaluation of des_ignsfor enhancing survivability. Sincethe DMEA utilizes the failure mode information from the FMEA, it should not beimposed without imposition of the FMEA. The DMEA, like the initial FMEA,should he done early in the conceptual phase to provide data related to thecapability of the conceptual weapon system design to survive the effects ofthe specified hostile threats. Development of this data before weapon systemdesiqn configuration is finalized will provide significant survivabilitybenefits with minimal impact on cost <strong>and</strong> schedule.50.6 FMECA plan (Task 105). The FMECA plan provides the contractor’splans <strong>and</strong> activities for implementing the FMECA tasks. The plan is used bythe procuring activity to evaluate the planned FMECA task efforts, <strong>and</strong> whenapproved, is used for monitoring contractor Implementation of the tasks. Theplan can be required as a separate document submittal or it can be included aspart of the Reliability Program Plan. The FMECA plan includes a descriptionof the contractor’s procedures for implementing the tasks <strong>and</strong> provides a crossindex showing the relationship of coincident performance <strong>and</strong> use of the FPEAtasks to preclude duplication of ef[ort. Sample contractor formats used inperformance of each FMECA task are <strong>Inc</strong>luded as a part of each task specifiedin the contract statement of work.50.7 Criticality number (Cr) calculation example. Calculation ofmeaningful criticality numbers requires the use of specific failure rate <strong>and</strong>part configuration data. When part configurations are known, failure ratedata can be obtained from the appropriate reliability prediction, field datafrom past systems of similar design <strong>and</strong> environmental use, or failure ratedata sources such as <strong>MIL</strong>-I{DBK-217. With known failure rates, the criticalitynumber for an item is the number of failures of a specific type expected permillion hours due to the item’s failure modes under a particular severityclassification as discussed in Task 101. A failure mode criticality number,Cm, for a particular severity classification is given by the expression:cm= f3aApt(1)The item criticality number, C , under ais then calculated by summing [he Cm forclassification. This sunwnation is givenparticular severity classification,each failure mode under that severityby the expressions:Cr = Z (Cm)nn=lOr(2)7 June 1983A-4
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