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)ences the form, performance, reliability or survival ofan item.Equipment repair time. The 50th percentile, i.e., themedian, of the distribution of repair time.Expert system. An intelligent computer system that usesknowledge and inference procedures to solve problemsthat are difficult enough to require significant humanexpertise in their solution.FFailure. A detected cessation of ability to perform a specifiedfunction or functions, within previously establishedlimits, in the area of interest. It is a malfunctionthat is beyond adjustment by the operator by means ofcontrols normally accessible to him during the routineoperation of the device.Failure analysis. The logical, systematic examination ofan item to identify and diagnose the cause of observedfailures.Failure effect. The condition(s) introduced by a failurethat reduce or modify the ability of an item to performits required function.Failure mode, effects, and criticality analysis (FMECA).A general evaluation procedure that1. Documents all possible potential failures in an itemdesign2. Determines by analysis the effect of each potentialfailure on item operation and on each reliability andmaintainability parameter applicable to the type ofitem3. Ranks potential failures according to their impact(see CRITICALITY) on each applicable systemreliability and maintainability parameter.Failure rate. The number of failures of an item per unitmeasure of use—cycles, time, miles, events, etc., asapplicable. It is also called renewal rate.Fault correction time. That element of active repair timerequired under a specified maintenance philosophy tocorrect the malfunction. It may consist of correcting themalfunction with the faulty item in place, removing andreplacing the item with a like serviceable item, or removingthe item for corrective maintenance and reinstallingthe same item.Fault detection time. Time between the occurrence of afailure and the point at which it is recognized that thesystem or equipment does not respond to operationaldemand during the mission sequence.required for testing and analyzing an item to isolate amalfunction.Field maintenance. Maintenance authorized and performedby designated maintenance activities in supportof using organizations.Final test time. That element of active repair timerequired after completion of maintenance, adjustments,and calibration to verify by measurement of performancethat the item is in a condition to perform itsfunction satisfactorily.Free time. Time during which operational use of a systemor equipment is not required; this time may or may notbe downtime, depending on whether or not the systemis in operable condition.Frequency-of-use-principle (equipment design). Theprinciple of positioning the most frequently maintaineditems in preferred locations to facilitate maintenance.Full-scale development phase. The third phase in themateriel acquisition process. During this phase, asystem –including all items necessary for its support—is fully developed and engineered, fabricated, tested,and initially type classified. Concurrently, nonmaterialaspects required to field an integrated system arerefined and finalized.Function analysis for maintainability. The analyticalbasis for allocating tasks to personnel and equipmentso as to achieve optimum system maintainability.Functional interchangeability. A condition in which apart or unit, regardless of its physical specifications.can perform the specific functions of another part orunit.Functional principle (equipment design). The principle ofarrangement that provides for the grouping of hardwareitems according to their functions.GGeneral-purpose test equipment. A category of testequipment, normally available in the supply system orfrom commercial stock, that can be used to test morethan one system or equipment type.Geometric mean-time-to-repair (MTTRG). A measure ofcentral tendency for repair time. Generally used withthe lognormal distribution.Go/no-go display. A display that indicates the operableor nonoperable condition of equipment.Fault location time. That element of active repair timeG-4
Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.HHuman engineering. The area of human factors that appliesscientific knowledge to the design of items toachieve effective operation, maintenance, and man/machine integration.Human factors. Human characteristics relative to complexsystems and the development and application ofprinciples and procedures for accomplishing optimumman/machine integration and utilization. The term isused in a broad sense to cover all biomedical and psychosocialconsiderations pertaining to man in thesystem.IInactive time. The period of time when the item is available,but it is neither needed nor operated for itsintended use.Indirect maintenance resources. That time in man-hoursand material in dollars which. although not directlyexpended in active maintenance tasks, contributes tothe overall maintenance mission through the support ofoverhead operations, administration, accumulation offacility records and statistics, supervision, and facilitiesupkeep.Inherent value. A measure of maintainability whichincludes only the effects of item design and applicationand assumes an ideal operation and support environment.In-process review (IPR) (nonmajor hardware systems). Areview conducted at critical points in the acquisitionprocess to evaluate military utility, accomplish effectivecoordination, and facilitate proper and timely decisions.Interchangeability. A condition when two or more partsare physically and functionally interchangeable in allpossible applications, i.e., when both parts are capableof full, mutual substitution in all directions.Intermediate maintenance. A category of maintenanceorganized as forward and rear. Forward maintenance ischaracterized by high mobility and repair by replacement,Division maintenance units will support maneuverelements, and nondivisional units will providearea and backup support to the division. Rear intermediatemaintenance is characterized by semifixed facilities.Its fundamental purpose is to support the theatersupply system through repair of components and directexchange of items.Item. A nonspecific term used to denote any product,including systems, materials, parts, subassemblies, sets,accessories. etc.DOD-HDBK-791(AM)Item obtainment time. The time required for the technicianto obtain replacement parts, assemblies, or units,depending on the maintenance concept and the locationand method of storing the supply items.LLife cycle costs. The sum of the funds expended duringthe life cycle of materiel for development, test, procurement,operation, support, and disposal.Line-replaceable unit (LRU). An item whose removal andreplacement with a like serviceable item is consideredthe optimum corrective method for a specific higherindenture level item.Logistic resources. The support personnel and materielrequired by an item to assure its mission performance.It includes such things as tools, test equipment, repairparts, facilities, technical manuals, and administrativeand supply procedures necessary to assure the availabilityof these resources when needed.Logistic support. Maintenance and supply support to beprovided at unit and intermediate and depot levels.Logistic support is influenced by the degree of unitizationor modularization, ruggedness, cost, test points,test equipment, tactical employment, and transportationrequirements.Logistic time. The portion of downtime attributable todelay in the acquisition of replacement parts.Logistics. Those aspects of military operations which dealwith (a) design and development, acquisition, storage,movement, distribution, maintenance, evacuation, anddisposal of materiel, (b) movement, evacuation, andhospitalization of personnel, (c) acquisition or construction,maintenance. operation and disposition offacilities, and (d) acquisition or furnishing of services.MMaintainability. A measure of the ease and rapidity withwhich a system or equipment can be restored to operationalstatus following a failure or retained in a specifiedcondition. It is characteristic of equipment designand installation, personnel availability in the requiredskill levels, adequacy of maintenance procedures andtest equipment, and the physical environment underwhich maintenance is performed. One expression ofmaintainability is the probability that an item will beretained in or restored to a specified condition within agiven period of time when the maintenance is performedin accordance with prescribed procedures andresources.G-5
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