| Term | Definition |
|---|---|
| ACCESSIBILITY | A measure of the relative ease of admission to the various areas of an item for the purpose of operation or maintenance. |
| ACTIVE CORRECTIVE MAINTENANCE TIME | That part of active maintenance time during which actions of corrective maintenance are performed on an item. Excluded are logistics and administrative delays (e.g., awaiting parts, shift change, etc.). |
| ACTIVE TIME | That time during which an item is in an operational inventory. |
| ADMINISTRATIVE TIME | That element of delay time, not included in the supply delay time. |
| ALIGNMENT | Performing the adjustments that are necessary to return an item to specified operation. |
| AMBIGUITY | The inability to distinguish which of two or more subunits of a product or item has failed. |
| AMBIGUITY GROUP | The number of possible subunits of a product or item identified by BIT, ETE, or manual test procedures, which might contain the failed hardware or software component. |
| AUTOMATIC TEST EQUIPMENT (ATE) | Equipment that is designed to automatically conduct analysis of functional or static parameters and to evaluate the degree of UUT (Unit Under Test) performance degradation; and may be used to perform fault isolation of UUT malfunctions. The decision making, control, or evaluative functions are conducted with minimum reliance on human intervention and usually done under computer control. |
| AVAILABILITY | A measure of the degree to which an item is in an operable and committable state at the start of a mission when the mission is called for at an unknown (random) time. (Item state at start of a mission includes the combined effects of the readiness-related system R & M parameters, but excludes mission time.) |
| BENCHMARKING | The practice of rating an organizations practices, designs, and processes against the world's best for the purpose of defining and implementing improvements. |
| BUILT-IN TEST EQUIPMENT (BITE) | Any device permanently mounted in the prime product or item and used for the express purpose of testing the product or item, either independently or in association with external test equipment. |
| BUILT-IN-TEST (BIT) | An integral capability of the equipment which provides an on-board, automated test capability, consisting of software or hardware (or both) components, to detect, diagnose, or isolate product (system) failures. The fault detection and, possibly, isolation capability is used for periodic or continuous monitoring of a system's operational health, and for observation and, possibly, diagnosis as a prelude to maintenance action. |
| BURN-IN | The operation of an item under stress to stabilize its characteristics. |
| CALIBRATION | A comparison of a measuring device with a known standard and a subsequent adjustment to eliminate any differences. Not to be confused with alignment. |
| CHECKOUT | Tests or observations of an item to determine its condition or status. |
| CHECKOUT TIME | That element of maintenance time during which performance of an item is verified to be a specified condition. |
| COMPONENT | Within a product, system, subsystem, or equipment, a component is a constituent module, part, or item. |
| Consumer's Risk | Used in conjunction with statistical testing. The probability of a customer accepting an item which would be proven bad if the test was conducted for an infinite time (or population). |
| CONTROL CHARTS | Statistical charts derived from measuring production processes that are used to identify variation that designers must account for to result in a robust design. |
| CORRECTIVE ACTION | A documented design, process, procedure, or materials change implemented and validated to correct the cause of failure or design deficiency. |
| CORRECTIVE MAINTENANCE (CM) | All actions performed as a result of failure, to restore an item to a specified condition. Corrective maintenance can include any or all of the following steps: Localization, Isolation, Disassembly, Interchange, Reassembly, Alignment and Checkout. |
| CRITICALITY | A relative measure of the consequence of a failure mode and its frequency of occurrence. |
| CUMULATIVE DISTRIBUTION FUNCTION (CDF) | A function that gives the probability that a random variable will be less than or equal to a specific value. |
| DEGRADATION | A gradual impairment in the ability to perform a function. |
| DEMONSTRATION | That which has been measured by the use of objective evidence gathered under specified conditions. |
| DEPENDABILITY | A measure of the degree to which an item is operable and capable of performing its required function at any (random) time during a specified mission profile, given item availability at the start of the mission. |
| DERATING | Using an item in such a way that applied stresses are below rated values, r lowering the rating of an item in one stress field to allow an increase in another stress field. |
| DESIGN MAINTAINABILITY | A measure of inherent maintainability that includes only the effects of an item design and its application, but which is derived from the level of maintainability required in a specific operational and support environment. |
| DETECTABLE FAILURE | Failures at the component, equipment, subsystem, or system (product) level that can be identified through periodic testing or revealed by an alarm or an indication of an anomaly. |
| DFR Effectiveness Ratio - Identification | The DFR Effectiveness Ratio Identification is defined as the total number of unanticipated failure modes discovered during test, manufacturing and/or field operation to the total number of failure modes discovered: Note that there are subsets of this metric that can be applied to individual phases in the total system life cycle, such as DFREff Design Identification, DFREff Process Identification, DFREff Mfg Process Identification, DFREff Test Identification, and DFREff O&S Identification. |
| DFR Effectiveness Ratio - Mitigation | The DFR Effectiveness Ratio Mitigation is defined as the total number of unexpected failure modes discovered during test, manufacturing and/or field operation to the total number of failure modes discovered: Note that there are subsets of this metric that can be applied to individual phases in the total system life cycle, such as DFREff Design Mitigation, DFREff Process Mitigation, DFREff Mfg Process Mitigation, DFREff Test Mitigation, and DFREff O&S Mitigation. |
| DFR Effectiveness Ratio - Total | The Design for Reliability (DFR) Effectiveness Ratio - Total is defined as the sum of the DFR Effectiveness Ratio Identification and the DFR Effectiveness Ratio Mitigation: |
| DIAGNOSTICS | The hardware, software, or other documented means used to determine that a malfunction has occurred and to isolate the cause of the malfunction. Also refers to the action of detecting and isolating failures or faults. |
| DIRECT MAINTENANCE MANHOURS PER MAINTENANCE ACTION (DMMH/MA) | A measure of the maintainability parameter related to item demand for maintenance labor. The sum of direct maintenance labor hours divided by the total number of preventive and corrective maintenance actions during a stated period of time. |
| DIRECT MAINTENANCE MANHOURS PER MAINTENANCE EVENT (DMMH/ME) | A measure of the maintainability parameter related to item demand for maintenance labor. The sum of direct maintenance labor hours, divided by the total number of preventive and corrective maintenance events during a stated period of time. |
| DISASSEMBLE | Opening an item and removing a number of parts or subassemblies to make the item that is to be replaced accessible for removal. This does not include the actual removal of the item to be replaced. |
| DORMANT | A state in which a system or equipment is not subject to stresses associated with its normal function. |
| DOWNING EVENT | The event that causes an item to become unavailable to initia its mission (the transition from uptime to downtime). |
| DOWNTIME | That element of time during which an item is in an operational inventory but is not in condition to perform its required function. |
| DURABILITY | A measure of the useful life of an item. |
| ELEMENT MAINTENANCE ACTION | A unit of work into which a maintenance activity may be broken down at a given indenture level. |
| ENVIRONMENT | The aggregate of all external and internal conditions either natural or man-made, or self-induced, that influences the form, performance, reliability or survival of an item. |
| Environmental Stress Screening (ESS) | A series of tests conducted under environmental stress often greater than experienced in normal operation to disclose weak parts and workmanship defects to be corrected. |
| EQUIPMENT | A general term designating an item or group of items capable of performing a complete function. |
| Exit Criterion (Milestone Threshold) | The exit criterion, or milestone threshold, represents the pre-determined quantitative reliability value that must be met or exceeded in order for the system/product to be authorized to enter the next test phase. Threshold values are computed at specific, predefined points in time. These milestones represent major decision points that may be specified in terms of cumulative hours, miles, etc. Specifically, a threshold value is a reliability value that corresponds to a particular percentile point of an ordered distribution of reliability values. A reliability point estimate, based on actual observed failure data, that falls at or below a threshold value (borderline between an accept/reject region) indicates that the achieved system/product reliability is not statistically in conformance with the IGC. |
| FAILURE | The event, or inoperable state, in which any item or part of an item does not, or would not, perform as previously specified. |
| FAILURE ANALYSIS | The logical systematic examination of an item (subsequent to failure), its construction, application, and documentation to identify the failure mode and determine the failure mechanism and its basic course. |
| FAILURE CATASTROPHIC | A failure that can cause item loss. |
| FAILURE CRITICAL | A failure, or combination of failures, that prevents an item from performing its specified mission. |
| FAILURE DEPENDENT | A failure that is caused by the failure of an associated item. |
| FAILURE EFFECT | The consequence(s) a failure mode has on the operation, function, or status of an item. Failure effects are typically classified as local, next higher level, and end. |
| FAILURE INDEPENDENT | A failure which occurs without being caused by the failure of another item. |
| FAILURE INTERMITTENT | Failure for a limited period of time, followed by the item's recovery of its ability to perform within specified limits without any remedial action. |
| FAILURE MECHANISM | The physical, chemical, electrical, thermal or other process which results in failure. |
| FAILURE MODE | The consequence of the mechanism through which the failure occurs, i.e., short, open, fracture, excessive wear. |
| FAILURE MODE AND EFFECTS ANALYSIS (FMEA) | A procedure by which each potential failure mode in a product (system) is analyzed to determine the results or effects thereof on the product and to classify each potential failure mode according to its severity or risk probability number. |
| FAILURE RANDOM | A failure whose occurrence is predictable only in a probabilistic or statistical sense. |
| Failure Rate | The total number of failures within an item population, divided by the total time expended by that population, during a particular measurement interval under stated conditions. |
| FAILURE RATE | The total number of failures within an item population, divided by the total number of life units expended by the population, during a particular measurement interval under stated conditions. |
| FALSE ALARM | A fault indicated by BIT or other monitoring circuitry where no fault can be found or confirmed. |
| FALSE ALARM RATE (FAR) | The frequency of occurrence of false alarms over a defined period of measure (e.g., time, cycles, etc.). |
| FAULT | Immediate cause of failure (e.g., maladjustment, misalignment, defect, etc.). |
| FAULT DETECTION (FD) | A process which discovers the existence of faults. |
| FAULT ISOLATION (FI) | The process of determining the location of a fault to the extent necessary to effect repair. |
| FAULT ISOLATION TIME | The time spent arriving at a decision as to which items caused the system to malfunction. This includes time spent working on (replacing, attempting to repair, and adjusting) portions of the system shown by subsequent interim tests not to have been the cause of the malfunction. |
| FAULT LOCALIZATION | The process of determining the location of a fault to the extent necessary to effect repair. |
| FAULT TREE ANALYSIS | An analytical process of examining a product or system to determine the impact of lower level failures on performance. |
| Fix Effectiveness Factor (FEF) | The fix effectiveness factor (FEF) is the fraction reduction in an individual failure mode failure rate due to the implementation and verification of an effective corrective action. For example, a FEF of 0.80 implies that 80% of an item failure mode failure rate has been removed based on an effective corrective action (Note that 0.20 of that failure rate remains). When data is available, the FEF is calculated as: Note that the closer the corrective action comes to mitigating the true root cause of the failure mode, the higher the resulting FEF will be. It is best to measure the actual value of the FEF as additional testing or field operation accumulates. However, in many instances, subjective judgment is used to assign a FEF. MIL-HDBK-189A contains guidelines. Any subjective assignment of an FEF should be supported by sound, documented rationale in order to be considered valid. |
| FRACTION OF FAULTS DETECTABLE (FFD) | That fraction of all failures that occur over operating time, t, that can be correctly identified through direct observation or other specified means by an operator or by maintenance personnel under stated conditions. |
| FRACTION OF FAULTS ISOLATABLE (FFI) | That fraction of all failures that occur over operating time, t, that can be correctly isolated to n or fewer units at a given maintenance level through the use of specified means by maintenance personnel under stated conditions. |
| Growth Potential (GP) | Growth potential is defined as the theoretical upper limit on reliability growth, which corresponds to the reliability performance that would result if all B-Modes were surfaced and fixed, with a feasible and justifiable FEF. |
| Hazard Rate | Instantaneous failure rate. At any point in the life of an item, the incremental change in the number of failures per associated incremental change in time. |
| Homogeneous Poisson Process (HPP) | A HPP is defined as a Poisson process such that the rate of occurrence of events within equal intervals is a constant with respect to the test duration. |
| Idealized Growth Curve (IGC) | An IGC is a planned growth curve that consists of a single smooth curve portraying the expected overall reliability growth pattern across test phases, and is based on (a) initial conditions, (b) assumed growth rate, and/or (c) planned management strategy. |
| INACTIVE TIME | That time during which an item is in reserve. (In an inactive inventory). |
| INHERENT AVAILABILITY(Ai ) | A measure of availability that includes only the effects of an item design and its application, and does not account for effects of the operational and support environment. |
| INHERENT RELIABILITY/INHERENT MAINTAINABILITY | A measure of reliability or maintainability that includes only the effects of an item design and its application, and includes an ideal operation and support environment. |
| INITIAL DELAY TIME | The time between the moment the product becomes available for maintenance and the moment work is commenced. |
| INITIAL ISOLATION | Isolation to the product subunit which must be replaced on line to return the product to operation. A subunit can be a modular assembly, or a component such as a crystal or antenna subsection. In the event that the maintenance concept requires a subunit to be removed, repaired and then replaced in the product, initial isolation includes both isolation to the failed subunit and isolation to the failed and removable portion of the subunit. |
| INITIAL ISOLATION LEVEL OF AMBIGUITY | The initial number of possible product subunits, identified by the built-in-test, built-in-test equipment, external test equipment, or manual test procedure, which might contain the failed component. |
| INTEGRATED DIAGNOSTICS | A structured process which maximizes the effectiveness of diagnostics by integrating pertinent elements, such as testability, automatic and manual testing, training, maintenance aiding, and technical information as a means for providing a cost effective capability to unambiguously detect and isolate all faults known or expected in items and to satisfy system mission requirements. Products of this process are hardware, software, documentation, and trained personnel. |
| INTERCHANGE | Removing the item that is to be replaced, and installing the replacement item. |
| INTERCHANGEABILITY | The ability to interchange, without restriction, like equipments or portions thereof in manufacture, maintenance, or operation. Like products are two or more items that possess such functional and physical characteristics as to be equivalent in performance and durability, and are capable of being exchanged one for the other without alteration of the items themselves or of adjoining items, except for adjustment, and without selection for fit and performance." |
| ISOLATION | Determining the location of a failure to the extent possible, by the use of accessory equipment. |
| LEVELS OF MAINTENANCE | The division of maintenance, based on different and requisite technical skills, by 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 PROFILE | A time-phased description of the events and environments that an item experiences from manufacture to final expenditures or removal form the operating inventory, to include one or more mission profiles. |
| LIFE UNITS | A measure of the duration applicable to an item (e.g. operating hours, cycles, distance, rounds fired, attempts to operate, etc.). |
| 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. |
| MMAX | The maximum repair/fix time associated with some percentage of all possible system repair/fix actions. (e.g., 95% of all repair/fix actions must be accomplished in less than one hour). |
| 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 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. |
| Management Strategy (MS) | The management strategy is defined as the fraction of the initial failure intensity due to failure modes that would receive corrective action if they were discovered during a developmental test program (fraction of unique B-Modes to total unique failure modes). |
| MAXIMUM CORRECTIVE MAINTENANCE TIME FOR A PRESCRIBED PERCENTILE ( M max ct) | 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. 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 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 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 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-Downtime (MDT) | The average time a system is unavailable for use due to a failure. Time includes the actual repair/fix time plus all delay time associated with a repairman arriving with the appropriate replacement parts. |
| Mean-Time-Between-Critical-Failure (MTBCF) | A measure of system reliability which includes the effects of any fault tolerance which may exist. The average time between failures which cause a loss of a system function defined as "critical" by the customer. |
| Mean-Time-Between-Failure (MTBF) | A basic measure of reliability for repairable items. The average time during which all parts of the item perform within their specified limits, during a particular measurement period under stated conditions. |
| Mean-Time-Between-Repair (mtbr) | A basic measure of reliability for repairable fielded systems. The average time between all system maintenance actions requiring removal and replacement of a box or subsystem. |
| Mean-Time-To-Failure (MTTF) | A basic measure of reliability for nonrepairable systems. Average failure free operating time, during a particular measurement period under stated conditions. |
| Mean-Time-to-Repair (MTTR) | A basic measure of maintainability. The sum of corrective maintenance times divided by the total number of failures within an item. The average time it takes to fully repair/fix a failed system. Typically includes fault isolation, remove and replacement of failed item(s) and checkout. (Also called mean corrective maintenance time, MCT). |
| MISSION PROFILE | A time phased description of the events and environments an item experiences from initiation to completion of a specified mission, to include the criteria for mission success or critical failures. |
| 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. |
| 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. |
| Non-Homogeneous Poisson Process (NHPP) | A NHPP is a Poisson process with a non-constant rate of occurrence of events within equal test intervals over the test duration. |
| 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 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 RELIABILITY/OPERATIONAL MAINTAINABILITY | A measure of the reliability or maintainability that includes the combined effect of the item design, installation, quality, environment, operation maintenance and repair. |
| 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). |
| Planned Growth Curve (PGC) | A PGC is a plot of the anticipated system reliability versus test duration during a development program. The PGC is constructed on a phase-by-phase basis. As such, it may consist of more than one growth curve. |
| Poisson Process | A Poisson process is a counting process for the number of events that occur during a test interval, where the test duration is measured as a function of hours, miles, cycles, operations, etc. |
| PREDICTED | That which is expected at some time in the future, postulated on analysis of past experience and tests. |
| 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. |
| Preventive Maintenance (PM) | Time associated with the performance of all required preventive maintenance, both scheduled and unscheduled. Usually expressed in terms of hours per year. |
| Producer's Risk | Used in conjunction with statistical testing. The probability of a customer rejecting an item which would be proven good if the test was conducted for an infinite time (or population). |
| Quality Function Deployment | A system that focuses on exactly what the customer wants. Activities which dont contribute to customer goals are considered wasteful and are eliminated. |
| 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. |
| REDUNDANCY, ACTIVE | That redundancy wherein all redundant items are operating simultaneously. |
| REDUNDANCY, STANDBY | That redundancy wherein the alternative means of performing the function is not operating until it is activated upon failure of the primary means of performing the function. |
| 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 GROWTH | The improvement in a reliability parameter caused by the successful correction of deficiencies in an item design or manufacture. |
| Reliability Growth Planning Curve | A reliability growth curve that reflects program schedules, the amount of testing, the available resources, and the realism of the test program towards achieving its reliability objectives. There are two types of curves: the Idealized Growth Curve (IGC) and the Planned Growth Curve (PGC) |
| Reliability Growth Projection | Reliability growth projection is an assessment of the reliability that can be anticipated/achieved at some point in the future. The potential rate of reliability improvement is determined by (a) the robustness and constancy of the FD/SC, (b) the on-going rate at which new problem modes are being surfaced, (c) the effectiveness and timeliness of the fixes, and (d) the set of failure modes that are addressed by the fixes (as determined by the MS). |
| Reliability Growth Tracking Curve | A reliability growth tracking curve is a plot of the best statistical representation of planned system reliability-to-demonstrated system reliability over the total test duration. This curve represents the best statistical representation in comparison to the family of growth curves assumed for the overall reliability growth of the system. |
| 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. |
| REPAIRABLE ITEM | An item that can be restored to perform all of its required functions by corrective maintenance. |
| 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. |
| Robust Design | A design approach that accounts for limitations in production capabilities, such as accounting for production machinery tolerance limitations. |
| 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. |
| SCREENING | A process of inspecting items to remove those that are unsatisfactory or those likely the exhibit early failure. |
| 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. |
| SINGLE POINT FAILURE | The failure of an item which would result in the failure of the system and is not compensated for by redundancy or alternative operational procedure. |
| STORAGE LIFE | The length of time an item can be stored under specified conditions and still meet specified 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 | 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. |
| 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. |
| TEST-ANALYZE-AND-FIX (TAAF) | (see Reliability Growth) |
| 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. |
| 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. |
| Unanticipated Failure Mode | An unanticipated failure mode is defined as a failure mode that is discovered during testing, manufacturing or field operation that was not previously identified or accounted for (and therefore, could not be mitigated) in Design for Reliability (DFR) activities such as FMEA/FMECA, Fault Tree Analysis, Physics-of-Failure (PoF), Modeling and Simulation (M&S), etc. It may also be used to identify non-design related failure modes whose root causes are traced to quality issues, process problems, and documentation/procedural errors. This parameter can be quantified to reflect the relative robustness of a DFR process in proactively identifying failure modes during the design process. A large quantity/ percentage of unanticipated failure modes indicates that a necessary corrective action is to add robustness to the DFR activities to ensure that all potential failure modes are suitably identified through an improved DFR process. Reducing the unanticipated failure mode metric has a positive impact on reliability growth. |
| Unexpected Failure Mode | An unexpected failure mode is defined as a failure mode that is discovered during testing, manufacturing or field operation that was previously accounted for in DFR activities, but was thought to have been suitably mitigated. As a consequence, the corrective actions taken to mitigate the failure mode prior to testing/fielding were not sufficient to preclude its occurrence relative to expectations. This parameter can be quantified to reflect the relative robustness of a DFR process in proactively mitigating failure modes during the design process. A large quantity/percentage of unexpected failure modes indicates that a necessary corrective action is to add robustness to the DFR process by improving design guidelines, rules, documentation, etc., to do a better job in mitigating identified failure modes. Reducing the unexpected failure mode metric has a positive impact on reliability growth. |
| UNSCHEDULED MAINTENANCE | Corrective maintenance performed in response to a suspected failure. |
| UPTIME | That element of ACTIVE TIME during which an item is in condition to perform its required functions. (Increases availability and dependability). |
| 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." |