MAINTAINABILITY DESIGN TECHNIQUES METRIC - AcqNotes.com

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Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.DOD-HDBK-791(AM)cost reduction over the life of a system, maintainabilityengineering input is an essential clement in the evolutionof a system.1-4.2 MAINTAINABILITY PLANThe maintainability program will include the tasksnecessary to achieve and demonstrate the goals indicatedin par. 1-4. The various tasks and their relationships to theacquisition process are presented in MIL-STD-470 (Ref.9). A matrix illustrating these relationships is shown inTable 1-1. The degree of maintainability achieved willdepend on the imposed requirements and management’semphasis on maintainability. The tasks are not to beapplied indiscriminately: All maintainability requirementsdo not apply to all systems. Instead, they are to be tailoredas required by their users as appropriate to particularsystems or equipment program type, magnitude, andneed (Ref. 9). Tailoring (Ref. 9) is the process by whichindividual requirements of the selected specificaitions,standards, and related documents are evaluated to determinethe extent to which they are most suitable for aspecific system and equipment acquisition, and the modificationof these requirements to insure that each achievesan optimal balance between operational needs and costs.The tailoring process, however, must conform to provisionsof existing regulations governing rnaintainabilityprograms and take care not to exclude those requirementsthat are determined essential to meeting minimum operationalneeds.The elements that comprise the maintainability planare explicitly detailed in MIL-STD-470 (Ref. 9) andshould be used as a guide in plan preparation. MIL-STD-TABLE 1-1. APPLICATION MATRIX (Ref. 9)Code Definitions for Table: (1) Requires considerable interpretation of intent to be cost-effective.S = Selectively applicableG = Generally applicableC = Generally applicable to designchanges only(2) MIL-STD-470 is not the primary implementation document.Other MIL-STDs or Statement of Work requirements must beincluded to define or rescind the requirements. For example, MIL-STD-471 must be imposed to describe maintainability) demonstrationN/A = Not applicabledetails and methods.ACC = Maintainability Accounting (3) Appropriate for those task elements suitable to definition duringENG =MGT =FSD =PROD =Maintainability EngineeringManagementFull-scale developmentProduction(4)phaseDepends on physical complexity of the system unit being procured,its packaging. and its overall maintenance policy.1-6
Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.470 (Ref. 9) is very specific about the importance ofallocating and predicting maintainability. Thc basis forthe process must be linked closely to the equipment supportconcept, available maintenance manpower, andoptimum design for repair as a function of survivability,redundancy, and battle damage. To obtain a maintainability-friendlydesign, a partnership between industryand Government is necessary there must be an enhancedmanagement awareness of the maintainability requirementby both industry and Government managers duringthe acquisition process. Contractors will respond to DoDpriorities.1-4.3 VERIFICATION, DEMONSTRATION,AND EVALUATION OFMAINTAINABILITY REQUIREMENTSThe preparation of a plan that includes the elementsthat insure the system will have the characteristic of maintainabilitydesigned into it is an important first step.However, to assess system maintainability quantitatively,the provisions of the maintainability plan must be verified,demonstrated, and evaluated. Unless this is done, thequalitative descriptors good, maximum, optimum --described in par. l-l apply.MIL-STD-471 (Ref. 5) provides procedures and testmethods for the verification, demonstration, and evaluationof qualitative and quantitative maintainability requirements.‘These actions are performed in accordance withthe maintainability test plan described in par. 1-4.2. Thetime phasing of these actions relative to the acquisitionprocess is illustrated in Fig. 1-3. MIL-STD-471 also providesfor qualitative assessment of various integratedlogistic support factors related to and impacting theachievement of maintainability parameters and itemdowntime e.g., technical manuals, personnel, tools andtest equipment, maintenance concepts, and provisioning.AR 702-3 (Ref. 8) provides additional information ontesting the various maintainability parameters; responsibilitiesfor conducting the test; conduct of the tests; scoringof the tests; and evaluation of the maintainabilityfeatures; and evaluation of the maintainability features toidentify needed changes in equipment design or equipmentmaintenance—e.g., maintenance allocation chart—and revisions, as appropriate, to the maintenance plan/support concept.To be effective, the results of the evaluation analysesmust provide information to designers and managers sothat the analyses are actually causing change-—if required—in the design rather than recording data on the design thatexists. The timing and credibility of these analyses mustbe such that they are accepted as part of the design evaluation.A common flaw in many maintainability programsis to have the analyses separated from design activity bytime, distance, or organization. The role of the maintainabilityanalyses can often be an indicator of the importanceplaced upon these tasks by the design team.DOD-HDBK-791(AM)1-5 FEATURES TO FACILITATEMAINTAINABILITYMaintainability requirements, and the resulting maintenanceactions, must be supported by system design.Qualitative and quantitative requirements must be establishedto provide system design guidelines during systemdevelopment; it is mandatory that a system maintainabilityconcept be formulated prior to detailed design. Identificationof maintenance requirements is a key contributorto cost-effectiveness. When life cycle cost is minimized, amajor factor is ease of maintenance.Features that facilitate maintainability include the elementsof physical attributes, diagnostics, simplification,testability, inspectability, accessibility, and maintainabilitytime/cost design criteria commensurate with the maintainabilityprofile of the system. Each of these elements isconsidered by the maintainability engineer in his developmentof concepts, criteria, and technical requirementsto assure timely, adequate, and cost-effective support ofthe design and operational needs of the system. Physicalfeatures and pertinent questions that affect maintainabilityfollow:1. Accessibility. Can the item be reached easily forrepair or adjustment?2. Visibility. Can the item being worked on be seen?3. Testability. Can system faults be detected readilyand isolated to the faulty replaceable assembly level?4. Complexity. How many subsystems are in thesystem? How many parts are used? Are the parts standardor special purpose?5. lnterchangeabiliy. Can the failed or malfunctioningunit be readily replaced with an identical unit with norequirement for alteration and calibration?6. Identification and Labeling. Are componentsuniquely identified? Are the labels permanent, or are theyeasily erased or obliterated by operation or maintenanceactions? Are labels positioned to be easily read?7. Verification. Can it be easily verified that therepaired item is functioning correctly?8. Simplicity. Is the design as simple as possible? Arestandard parts and tools used? Are functions and partsconsolidated?Pertinent questions to be asked concerning the rationaleto be considered in assessing the previous designfeatures are1. Are features compatible with maintainabilityresource developments?2. Is the system friendly to maintenance in providingaccessibility, fault isolation capability, and packaging forreliability?3. Can calibration and precision measurements beeasily and readily accommodated or the need totallyeliminated?4. Is the system packaged for fault isolation and1-7
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