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LEVELS OF MAINTENANCE: The division of maintenance, based on different and requisite technical skill, which jobs are allocated to organizations in accordance with the `availability of personnel, tools, supplies, and the time within the organization. Within the DoD, typical maintenance levels are organizational, intermediate and depot.
LIFE CYCLE COST (LCC): The sum of acquisition, logistics support, operating, and retirement and phase-out expenses.
LIFE CYCLE PHASES: Identifiable stages in the life of a product from the development of the first concept to removing the product from service and disposing of it. Within the Department of Defense, four phases are formally defined: Concept Exploration; Program Definition and Risk Reduction; Engineering and Manufacturing Development; and Production, Deployment, and Operational Support. Although not defined as a phase, demilitarization and disposal is defined as those activities conducted at the end of a product's useful life. Within the commercial sector, various ways of dividing the life cycle into phases are used. One way is: Customer Need Analysis, Design and Development, Production and Construction, Operation and Maintenance, and Retirement and Phase-out.
LINE REPLACEABLE UNIT (LRU): A unit designed to be removed upon failure from a larger entity (product or item) in the operational environment, normally at the organizational level.
LOCALIZATION: Determining the location of a failure to the extent possible, without using accessory test equipment.
LOGISTIC TIME: That portion of downtime during which repair is delayed solely to waiting for a replacement part or other subdivision of the system.
LOGISTICS SUPPORT: The materials and services required to enable the operating forces to operate, maintain, and repair the end item within the maintenance concept defined for that end item.
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MAINTAINABILITY: The relative ease and economy of time and resources with which an item can be retained in, or restored to, a specified condition when maintenance is performed by personnel having specified skill levels, using prescribed procedures and resources, at each prescribed level of maintenance and repair. Also, the probability that an item can be retained in, or restored to, a specified condition when maintenance is performed by personnel having specified skill levels, using prescribed procedures and resources, at each prescribed level of maintenance and repair.
MAINTAINABILITY ACTIVITIES BLOCK DIAGRAM: A diagrammatic representation of the necessary order of the various maintenance activities involved with a maintenance task for an item. Three possible orders exist: simultaneous, sequential, and a combination of simultaneous and sequential.
MAINTAINABILITY ALLOCATION: The apportionment of numerical requirements to all levels within a product which will result in meeting the overall maintainability requirement or goal.
MAINTAINABILITY DEMONSTRATION: A formal test specifically designed to measure maintainability by the use of objective evidence gathered under specified conditions.
MAINTAINABILITY MODEL: A quantifiable representation of a test or process the purpose of which is to analyze results to determine specific relationships of a set of quantifiable maintainability parameters.
MAINTAINABILITY PREDICTION: That maintainability performance which is expected at some future time, postulated on analysis of models, test, and past experience.
MAINTENANCE: All actions necessary for retaining an item in or restoring it to a specified condition.
MAINTENANCE ACTION: An element of a maintenance event. One or more tasks (i.e., fault localization, fault isolation, servicing and inspection) necessary to retain an item in or restore it to a specified condition.
MAINTENANCE CONCEPT: A description of the planned general scheme for maintenance and support of an item in the operational environment. It provides a practical basis for design, layout, and packaging of the system and its test equipment. It establishes the scope of maintenance responsibility for each level of maintenance and the personnel resources required to maintain the system.
MAINTENANCE ENVIRONMENT: The climatic, geographical, physical and operational conditions (e.g., combat, mobile, continental) under which an item will be maintained.
MAINTENANCE EVENT: One or more maintenance actions required to effect corrective and preventive maintenance due to any type of failure or malfunction, false alarm or scheduled maintenance plan.
MAINTENANCE RATIO: A measure of the total maintenance manpower burden required to maintain an item. It is expressed as the cumulative number of labor hours of maintenance expended in direct labor during a given period of the life units divided by the cumulative number of end item life units during the same period.
MAINTENANCE TASK: The maintenance effort necessary for retaining an item in, or changing/restoring it to a specified condition.
MAINTENANCE TIME: An element of downtime which excludes modification and delay time.
MAXIMUM CORRECTIVE MAINTENANCE TIME FOR THE PERCENTILE ( M Max()): The maximum repair time associated with some percentage of all possible system corrective repair actions. (For example, 95% of all corrective repair actions must be accomplished in less than one hour.)
MEAN ACTIVE CORRECTIVE MAINTENANCE TIME (MACMT): The average time associated with active corrective maintenance actions. Time includes only actual repair time associated with a repair person performing corrective maintenance steps (i.e., Localization, Isolation, Disassembly, Interchange, Reassembly, Alignment, and Checkout).
MEAN DOWNTIME (MDT): The average time a system is unavailable for use due to a failure. Time includes the actual repair time plus all delay time associated with a repair person arriving with the appropriate replacement parts.
MEAN MAINTENANCE MANHOURS PER MAINTENANCE ACTION (MMH/MA): This term is defined in the same way as MMH/Repair except that time spent as a result of system failure false alarms must also be included in the maintenance labor hours.
MEAN MAINTENANCE MANHOURS PER REPAIR (MMH/REPAIR): The summation of the products of the mean maintenance labor hours expended to repair each given repairable item multiplied by the failure rate for the item, divided by the summation of the failure rates for all repairable items. The equation is given in MIL-HDBK-472, page V-7, as follows:
Also, the total maintenance labor hours required to perform all repairs at any specific level of maintenance, divided by the number of repairs.
MEAN MAINTENANCE TIME: The measure of maintainability taking into account maintenance policy. The sum of preventive and corrective maintenance times, divided by the sum of scheduled and unscheduled maintenance events, during a stated period of time.
MEAN MANHOURS PER FLYING HOUR (MMH/FH): A maintainability performance figure calculated by dividing the labor hours expended to maintain a particular aircraft fleet during a given period, by the flying hours during that period.
MEAN MANHOURS PER OPERATING HOUR (MMH/OH): The total labor hours required to maintain a system divided by the number of operating hours. This includes labor hours associated with: corrective maintenance, preventive maintenance, and maintenance caused by false alarms.
MEAN TIME BETWEEN FAILURE (MTBF): A basic measure of reliability for repairable items. The mean number of life units during which all parts of the item perform within their specified limits, during a particular measurement interval under stated conditions.
MEAN TIME BETWEEN CRITICAL FAILURE (MTBCF): A measure of mission or functional reliability. The mean number of life units during which the item performs its mission or function within specified limits, during a particular measurement interval under stated conditions.
MEAN TIME BETWEEN MAINTENANCE (MTBM): A measure of the reliability taking into account maintenance policy. The total number of life units expended by a given time, divided by the total number of maintenance events (scheduled and unscheduled) due to that item.
MEAN TIME BETWEEN MAINTENANCE ACTIONS (MTBMA): A measure of the product reliability parameter related to demand for maintenance labor. The total number of product life units, divided by the total number of maintenance actions (preventive and corrective) during a stated period of time.
MEAN TIME BETWEEN REMOVALS (MTBR): A measure of the product reliability parameter related to demand for logistic support: The total number of system life units divided by the total number of items removed from that product during a stated period of time. This term is defined to exclude removals performed to facilitate other maintenance and removals for product improvement.
MEAN TIME TO REPAIR (MTTR): A basic measure of maintainability. The sum of corrective maintenance times at any specific level of repair, divided by the total number of failures within an item repaired at that level, during a particular interval under stated conditions.
MEAN TIME TO RESTORE SYSTEM (MTTRS): A measure of the product maintainability parameter, related to availability and readiness: The total corrective maintenance time, associated with downing events, divided by the total number of downing events, during a stated period of time. (Excludes time for off-product maintenance and repair of detached components.)
MEAN TIME TO SERVICE (MTTS): A measure of an on-product maintainability characteristic related to servicing that is calculated by dividing the total scheduled crew/operator/driver servicing time by the number of times the item was serviced.
MISSION MAINTAINABILITY: The measure of the ability of an item to be retained in or restored to specified condition when maintenance is performed during the course of a specified mission profile. (The mission-related system maintainability parameter.)
MISSION TIME: That element of up time required to perform a stated mission profile.
MISSION-TIME-TO-RESTORE-FUNCTIONS (MTTRF): A measure of mission maintainability: The total corrective critical failure maintenance time, divided by the total number of critical failures, during the course of a specified mission profile.
MODIFICATION: Major engineering changes to an existing product or item to effect improvements in design capabilities or characteristics.
MTTR ELEMENTS: Corrective maintenance actions consisting of the following tasks:
- Preparation: Time associated with those tasks, including localization, required to be performed before fault isolation can be executed.
- Fault Isolation: Time associated with those tasks required to isolate the fault to the level at which fault correction begins.
- Disassembly: Time associated with gaining access to the replaceable item or items identified during the fault isolation process.
- Interchange: Time associated with the removal and replacement item or suspected faulty item.
- Reassembly: Time associated with closing up the equipment after interchange is performed.
- Alignment: Time associated with aligning the system or replaceable item after a fault has been corrected.
- Checkout: Time associated with the verification that a fault has been corrected and the product is operational.
- Start-Up: Time associated with bringing a product up to the operational state it was in prior to failure, once a fault has been corrected and the operational status of the product verified.
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NON-DEVELOPMENTAL ITEM (NDI): Any previously developed item used exclusively for governmental purposes by a Federal agency, a State or local government, or a foreign government with which the U.S. has a mutual defense cooperation agreement; any such item with minor modifications; and any item fully developed and in production but not yet in use. (See SD-2 or the Federal Acquisition Regulation Parts 6, 10, 11, 12 and 14, for a complete definition and criteria.)
NON-DESTRUCTIVE INSPECTION (NDI): Any method used for inspecting an item without physically, chemically, or otherwise destroying or changing the design characteristics of the item. However, it may be necessary to remove paint or other external coatings to use the NDI method. A wide range of technology is usually described as nondestructive inspection, evaluation, or testing (collectively referred to as non-destructive evaluation or NDE). The core of NDE is commonly thought to contain ultrasonic, visual, radiographic, eddy current, liquid penetrant, and magnetic particle inspection methods. Other methodologies, include acoustic emission, use of laser interference, microwaves, NMR and MRI, thermal imaging, and so forth.
NON-DETECTABLE FAILURE: Failures at the component, equipment, subsystem, or system (product) level that are identifiable by analysis but cannot be identified through periodic testing or revealed by an alarm or an indication of an anomaly.
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OPERATIONAL ENVIRONMENT: The aggregate of all external and internal conditions (such as temperature, humidity, radiation, magnetic and electric fields, shock vibration, etc.) either natural or man made, or self-induced, that influences the form, operational performance, reliability or survival of an item.
OPERATIONAL MAINTAINABILITY: The assessed maintainability of an item based on field data.
OPERATIONAL READINESS: The ability of a military unit to respond to its operation plan(s) upon receipt of an operations order. (A function of assigned strength, item availability, status, or supply, training, etc.).
OPERATIONAL TEST AND EVALUATION (OT&E): Test and evaluation which focuses on the development of optimum tactics, techniques, procedures, and concepts for products and items, evaluation of reliability, maintainability and operational effectiveness, and suitability of products and items under realistic operational conditions.
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PERCENT ISOLATION TO A GROUP OF RIs: The percent of time that detected failures can be fault isolated to a specified ambiguity group of size n or less, where n is the number of replaceable items (RIs).
PERCENT ISOLATION TO A SINGLE RI: The percent of time that detected failures can be fault isolated to exactly one replaceable item (RI).
PERFORMANCE SPECIFICATION (PS): A design document stating the functional requirements for an item.
PERFORMANCE-BASED REQUIREMENTS (SPECIFICATION): Requirements that describe what the product should do, how it should perform, the environment in which it should operate, and interface and interchangeability characteristics. They should not specify how the product should be designed or manufactured.
PREPARATION TIME: The time spent obtaining, setting up, and calibrating maintenance aids; warming up equipment; etc.
PREVENTIVE MAINTENANCE (PM): All actions performed in an attempt to retain an item in specified condition by providing systematic inspection, detection, and prevention of incipient failures.
PROCESS ACTION TEAM (PAT): A group of individuals with complementary skills, committed to a common purpose, set of performance goals, and approach for which they hold themselves accountable, who work together using shared knowledge and capabilities to improve business processes.
PROGRAM-UNIQUE SPECIFICATION. This type of Government specification, also called a system specification, establishes requirements for items used for a particular weapon system or program. Little potential exists for the use of the document in other programs or applications. It is written as a performance specification, but it may include a blend of performance and detail design type requirements.
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REASSEMBLY: Assembling the items that were removed during disassembly and closing the reassembled items.
REDUNDANCY: The existence of more than one means for accomplishing a given function. Each means of accomplishing the function need not necessarily be identical.
RELIABILITY: (1) The duration or probability of failure-free performance under stated conditions. (2) The probability that an item can perform its intended function for a specified interval under stated conditions. (For non-redundant items this is equivalent to definition (1). For redundant items this is equivalent to definition of mission reliability.)
RELIABILITY-CENTERED MAINTENANCE (RCM): A disciplined logic or methodology used to identify preventive and corrective maintenance tasks to realize the inherent reliability of equipment at a minimum expenditure of resources.
REPAIR TIME: The time spent replacing, repairing, or adjusting all items suspected to have been the cause of the malfunction, except those subsequently shown by interim test of the system not to have been the cause.
REPLACEABLE ITEM (RI) or REPLACEABLE UNIT (RU): An item, unit, subassembly, or part which is normally intended to be replaced during corrective maintenance upon failure of the item.
REQUEST FOR PROPOSAL (RFP): A letter or document sent to suppliers asking to show how a problem or situation can be addressed. Normally the supplier's response proposes a solution and quotes a price. Similar to a Request for Quote (RFQ), although the RFQ is usually used for products already developed.
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SCHEDULED MAINTENANCE: Periodic prescribed inspection and/or servicing of products or items accomplished on a calendar, mileage or hours of operation basis. Included in Preventive Maintenance.
SERVICING: The performance of any act needed to keep an item in operating condition, (i.e. lubricating, fueling, oiling, cleaning, etc.), but not including preventive maintenance of parts or corrective maintenance tasks.
STANDARD PERFORMANCE SPECIFICATION (SPS): A type of specification that establishes requirements for military-unique items used in multiple programs or applications.
STORAGE LIFE: The length of time an item can be stored under specified conditions and still meet specified operating requirements.
SUBSYSTEM: A combination of sets, groups, etc. which performs an operational function within a product (system) and is a major subdivision of the product. (Example: Data processing subsystem, guidance subsystem).
SUPPLY DELAY TIME: That element of delay time during which a needed replacement item is being obtained.
SUPPORT CONCEPT: A product-level description of maintenance needs consistent with an item's design and operational requirements.
SUPPORT ENVIRONMENT: The mobile, fixed and computer resources necessary for the operation and maintenance of a product under various environments but which are not physically part of the product. These resources are the people and the equipment required to make an item, product or facility operational as intended.
SYSTEM: General -A composite of equipment and skills, and techniques capable of performing or supporting an operational role, or both. A complete system includes all equipment, related facilities, material, software, services, and personnel required for its operation and support to the degree that it can be considered self-sufficient in its intended operational environment.
SYSTEM ADMINISTRATIVE TIME: System (product) downtime other than active maintenance time and logistic time.
SYSTEM DOWNTIME: The time interval between the commencement of work on a system (product) malfunction and the time when the system has been repaired and/or checked by the maintenance person, and no further maintenance activity is executed.
SYSTEM FINAL TEST TIME: The time spent confirming that a system (product) is in satisfactory operating condition (as determined by the maintenance person) following maintenance. It is possible for a system final test to be performed after each correction of a malfunction.
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TESTABILITY: A design characteristic which allows status (operable, inoperable, or degraded) of an item to be determined and the isolation of faults within the item to be performed in a timely manner.
TEST MEASUREMENT AND DIAGNOSTIC EQUIPMENT (TMDE): Any product or item used to evaluate the condition of another product or item to identify or isolate any actual or potential failures.
TEST POINT: A jack or similar fitting to which a test probe is attached for measuring a circuit parameter or waveform.
TIME, TURN AROUND: That element of maintenance time needed to replenish consumables and check out an item for recommitment.
TOTAL SYSTEM DOWNTIME: The time interval between the reporting of a system (product) malfunction and the time when the system has been repaired and/or checked by the maintenance person, and no further maintenance activity is executed.
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UNIT UNDER TEST (UUT): A UUT is any product or item (system, set, subsystem, assembly or subassembly, etc.) undergoing testing or otherwise being evaluated by technical means.
UNSCHEDULED MAINTENANCE: Corrective maintenance performed in response to a suspected failure.
UPTIME RATIO: A composite measure of operational availability and dependability that includes the combined effects of item design, installation, quality, environment, operation, maintenance, repair and logistic support: The quotient of uptime divided by the sum of uptime and downtime.)
UPTIME: That element of ACTIVE TIME during which an item is in condition to perform its required functions. (Increases availability and dependability).
USEFUL LIFE: The number of life units from manufacture to when the item has an unrepairable failure or unacceptable failure rate. Also, the period of time before the failure rate increases due to wearout.
UTILIZATION RATE: The planned or actual number of life units expended, or missions attempted during a stated interval of calendar time.
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VERIFICATION: The contractor effort to: (1) determine the accuracy of and update the analytical (predicted) data obtained from the maintainability engineering analysis; (2) identify maintainability design deficiencies; and (3) gain progressive assurance that the maintainability of the item can be achieved and be demonstrated in subsequent phases. This effort is monitored by the procuring activity from date of award of the contract, through hardware development from components to the configuration item (CI).
VIRTUAL REALITY: A combination of various interface technologies that enables a user to intuitively interact with an immersive and dynamic computer-generated environment.