MAINTAINABILITY DESIGN TECHNIQUES METRIC - AcqNotes.com

Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.DOD-HDBK-791(AM)CHAPTER 1INTRODUCTIONThe reasons for maintainability, i.e., reduced support costs and improved operational readiness—arepresented. Maintainability and maintenance are defined, and quantitative measures of maintainability areintroduced. The maintainability program encompassing its objectives, plan, and verification is discussed.Features that facilitate maintainability are listed. The importance of introducing these features as early aspossible into the design process is stressed.1-1 INTRODUCTIONMaintainability and reliability are the two major systemcharacteristics which combine to form the commonlyused effectiveness index availability. Although reliabiliyand maintainability share co-importance, maintainabilitymerits special consideration because of its influenceon system maintenance activities, i.e., the expenditureof man-hours and material, which represent significantbudgetary costs over the life of the system.Maintenance activities also reduce the operational readinessof a system.With the introduction of modern, complex materielresulting from sophisticated technology and the importanceof’ keeping the materiel combat ready and itspotential for higher failure rates and attendant increasedmaintenance actions, repairs could no longer be basedsolely on individual judgment and subjective analysis. Itbecame evident that "how much time is required toreplace or repair an item” was not the sole criterion,rather "how much time and skill are required to determinewhich item to replace or repair” and how to reduce theneed for maintenance or the simplification of the actionbecame equally important. The consideration of maintainabilityin designing a system is not a new conceptsystems were always designed to have “good”, “maximum”,or “optimum’’ maintainability. Unfortunately, theuse of these qualitative adjectives resulted in an “unknown”maintainability. New techniques, however, permitthe conversion of these subjective qualitative judgmentsinto an area of quantitative measurements. Thethreshold adopted by the US Army Materiel Command(AMC) is the operational requirement. Current AMCpolicy is to develop operational requirements in considerationof mission need, technical feasibility, and operatingand support costs; and to document the requirement inthe Decision Coordinating Paper (DCP) and SystemConcept Paper (SCP).Maintainability is a risk area not because the requirementsare not technically available: rather, it is a risk areabecause of the reluctance of the technical community tochange from its traditional emphasis on performance asopposed to maintainability.In summary, maintainability has emerged as an importantfactor of the design process and an inherent designcharacteristic that is truly quantitative in nature and.therefore, lends itself to specification. demonstration, andtrade-off analysis with such characteristics as reliabilityand logistic support. The implementation of this philosophyseeks the goals and objectives presented in par.1-4.1. For the maintainability engineer this means that theoptimum degree of maintainability must be incorporatedin system design. beginning as early as the concept phase.If the maintainability engineer, working with the designer,fails to accomplish this, he fails to achieve his objective—i.e., the provision of operational availability. A systemthat fails to perform at times cannot safely be planned,which renders it useless for combat operations.1-2 MAINTAINABILITY VSMAINTENANCEMaintainability is a characteristic of design and installation.This characteristic is the measure of the ability ofan item to be retained in or restored to a specified conditionwhen maintenance is performed by personnel havingspecified skill levels and using prescribed procedures andresources at each prescribed level of repair (Ref. l).Maintenance is essentially the response to the maintainabilityprogram, i.e., the series of actions necessaryfor retaining materiel in or restoring it to a serviceablecondition. Maintenance actions are of two types, i.e.,1. Corrective Maintenance. An action required whenequipment fails or malfunctions2. Preventive Maintenance. An action required tomaintain equipment in an operable condition throughperiodic servicing and/or replacement of components atspecified intervals. Preventive maintenance can, andshould, be conveniently scheduled to avoid interferencewith operating schedules. A detailed discussion of preventivemaintenance is presented in Chapter 8.Erroneously, corrective maintenance is referred to asunscheduled maintenance, and preventive maintenance isreferred to as scheduled maintenance. From a practicalstandpoint military personnel perform maintenance—both corrective and preventive-–whenever a window ofopportunity exists. The specific maintenance tasks are afunction of the reliability, availability maintainability,1-1