ACCESSIBILITY: A measure of the relative ease of
admission to the various areas of an item for the purpose of operation or
ACCEPTANCE TEST: A test
conducted under specified conditions by or on behalf of the customer, using
delivered or deliverable items, to determine whether or not the item satisfies
specified requirements. Includes acceptance of first production
ACHIEVED: Obtained as
verified by measurement, as in "achieved reliability performance."
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.
is a measure of how well customers can afford to purchase, operate, and
maintain a product over its planned service life. Affordability is a function
of product value and product costs. It is the result of a balanced design in
which long-term support costs are considered equally with near-term
development and manufacturing costs.
ALERT TIME: That time during
which a product is immediately ready to perform its function or mission if
required. No maintenance or other activities that would impede or slow the
start of the function or mission is permitted.
ALIGNMENT: Performing the
adjustments 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
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
descriptions and measurements of the physical body variations in people. These
are useful in human factors design.
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
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
BUILT-IN-TEST (BIT): An integral capability of
the mission equipment which provides an onboard, 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.
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.
BURN-IN: Also known as
preconditioning, burn-in is the operation of an item under stress to stabilize
its characteristics. Not to be confused with debugging.
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.
CHARGEABLE: Within the
responsibility of a given organizational entity. Used with terms such as
failures, maintenance time, etc.
CHECKOUT TIME: That element
of maintenance time during which performance of an item is verified to be a
CHECKOUT: Tests or
observations of an item to determine its condition or status.
COMMERCIAL ITEM: Any item,
other than real property, that is of a type customarily used for
nongovernmental purposes and that has been sold, leased, or licensed to the
general public, or has been offered for sale, lease, or license to the general
public; items evolved from these items that are not yet available in the
commercial market but will be in time to meet the delivery requirements of a
solicitation. (See “Buying Commercial and Non-Developmental Items: A
Handbook [SD-2, Apr 1996, OUSD/A&T]” or the Federal Acquisition
Regulation, Parts 6, 10, 11, 12 and 14, for a complete definition and
(COTS): Items available in a domestic or foreign commercial marketplace
and usually ordered by part number.
COMPONENT: Within a product,
system, subsystem, or equipment, a component is a constituent module, part, or
COMPUTER-AIDED DESIGN (CAD):
A process which uses a computer system to assist in the creation,
modification, verification, and display of a design.
CONFIGURATION ITEM (CI): A
collection of hardware and software which satisfies a defined end-use
function. The CI is designated for separate as-designed, as-built and
as-shipped content makeup management control.
CONTRACT DELIVERABLES REQUIREMENTS
LIST (CDRL): A listing of all technical data and information which the
contractor must deliver to the Customer.
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.
CRITICAL DESIGN REVIEW (CDR):
The comparative evaluation of an item and program parameters. It is usually
held just prior to production release after the item has reached a degree of
completion permitting a comprehensive examination and analysis.
CRITICALITY: A relative
measure of the consequence and frequency of occurrence of a failure
DATA ITEM DESCRIPTION (DID): A Government form
used to define and describe the written outputs required from a
DEBUGGING: A process to
detect and remedy inadequacies in an item. Not to be confused with burn-in,
fault-isolation, or screening.
DEGRADATION: A gradual
decrease in an item's characteristic or ability to perform.
DELAY TIME: That element of
downtime during which no maintenance is being accomplished on the item because
of either supply or administrative delay.
DEMONSTRATED: That which has
been measured using objective evidence gathered under specified and
DEMONSTRATION TEST: A test
conducted under specified conditions, by or on behalf of the customer, using
items representative of the production configuration, in order to determine
compliance with item design requirements as a basis for production approval
(also known as a Qualification Test).
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 that
the item is available at mission start. (Item state during a mission includes
the combined effects of the mission-related system R&M parameters but
excludes non-mission time; see availability.)
DERATING: (a) Using an
item in such a way that applied stresses are below rated values. (b)
The lowering of the rating of an item in one stress field to allow an
increase in another stress field.
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.
DEVELOPMENT TEST: Testing
performed during development and integration to ensure critical design
parameters are met, verify the performance of an item's design, and produce
data supporting design improvements. Development test, sometimes called
engineering test, also discloses deficiencies and verifies that corrective
action effectively prevents recurrence of these deficiencies. Properly done,
development test reduces the risk of redesign being necessary following
demonstration testing or delivery to the customer.
DEVELOPMENT TEST AND EVALUATION
(DT&E): Test and evaluation focused on the technological and
engineering aspects of the product (system, subsystem, or
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 an
item is able to but is not required to function. Most often associated with
long-term storage and "wooden" rounds. Not to be confused with
DOWNING EVENT: An event which
causes an item to become unavailable to begin a mission (i.e., the transition
from up-time to down-time).
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 an
item's useful life (a special case of reliability). Often referred to as
ENVIRONMENT: The aggregate of all external and
internal conditions (such as temperature, humidity, radiation, magnetic and
electrical fields, shock, vibration, etc.), whether natural, manmade, or
self-induced, that influences the form, fit, or function of an
ENVIRONMENTAL STRESS SCREENING
(ESS): A series of tests conducted under environmental stresses to
disclose weak parts and workmanship defects so that corrective action can be
EQUIPMENT: A general term
designating an item or group of items capable of performing a complete
FAILURE: The event, or inoperable state, in which
any item or part of an item does not, or would not, perform as previously
FAILURE ANALYSIS: Subsequent
to a failure, the logical systematic examination of an item, its construction,
application, and documentation to identify the failure mode and determine the
failure mechanism and its basic course.
FAILURE, CATASTROPHIC: A
failure that causes loss of the item, human life, or serious collateral damage
FAILURE, CRITICAL: A failure
or combination of failures that prevents an item from performing a specified
FAILURE, DEPENDENT: A failure
of one item caused by the failure of an associated item(s). A failure that is
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,
FAILURE, INDEPENDENT: A
failure of an item that is not caused by the failure of any other item. A
failure that is not dependent.
Failure for a limited period of time, followed by the item's recovery of its
ability to perform within specified limits without any remedial
FAILURE MECHANISM: The
physical, chemical, electrical, thermal or other process which results in
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 for analyzing each potential failure mode in a
product to determine the results or effects thereof on the product.
When the analysis is extended to classify
each potential failure mode according to its severity and probability of
occurrence, it is called a Failure Mode, Effects, and Criticality Analysis
FAILURE, NON-CHARGEABLE: (a)
A non-relevant failure. (b) A relevant failure caused by a
condition previously not specified as being the responsibility of a given
organizational entity. All relevant
failures are chargeable to one organizational entity or another.
FAILURE, NON-RELEVANT: (a)
A failure verified as having been caused by a condition not present in
the operational environment. (b) A failure verified as peculiar to
an item design that will not enter the operational, or active,
FAILURE, RANDOM: A failure,
the occurrence of which cannot be predicted except in a probabilistic or
FAILURE RATE: The total
number of failures within an item population, divided by the total number of
life units expended by that population, during a particular measurement period
under stated conditions.
FALSE ALARM RATE (FAR): The
frequency of occurrence of false alarms over a defined period of measure
(e.g., time, cycles, etc.).
FALSE ALARM: A fault
indicated by BIT or other monitoring circuitry where no fault can be found or
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
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 approximate location of a fault.
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
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
FUNCTIONAL TEST: An
evaluation of a product or item while it is being operated and checked under
limited conditions without the aid of its associated equipment in order to
determine its fitness for use.
GOVERNMENT-FURNISHED EQUIPMENT (GFE): An item
provided for inclusion in or use with a product or service being procured by
GUIDE SPECIFICATION: This is
a type of performance specification prepared by the Government. It identifies
standard, recurring requirements that must be addressed when developing new
systems, subsystems, equipments, and assemblies. Its structure forces
appropriate tailoring to meet user needs.
HUMAN ENGINEERING (HE): The application of
scientific knowledge to the design of items to achieve effective user-system
integration (man-machine interface).
HUMAN FACTORS: A body of
scientific facts about human characteristics. The term covers all biomedical
and psychosocial considerations; it includes, but is not limited to,
principles and applications in the areas of human engineering, personnel
selection, training, life support, job performance aids, work loads, and human
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. Sometimes referred to as "intrinsic"
INHERENT R&M VALUE: A
measure of reliability or maintainability that includes only the effects of an
item's design and application, and assumes an ideal operating and support
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.
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
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.
INTEGRATED PRODUCT TEAM: A
concurrent engineering team made up of individuals representing all relevant
disciplines associated with a product's design, manufacturing, and marketing.
All members work together using shared knowledge and capabilities to develop
and manufacture a product in which requirements are balanced. The individuals
must be committed to a common purpose, work to a unified set of requirements,
and hold themselves accountable for decisions made and actions
INTERCHANGE: Removing the
item that is to be replaced, and installing the replacement item.
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
INTERFACE DEVICE: An item
which provides mechanical and electrical connections and any signal
conditioning required between the automatic test equipment (ATE) and the unit
under test (UUT); also known as an interface test adapter or interface adapter
INVENTORY, ACTIVE: The group
of items assigned to an operational status.
INVENTORY, INACTIVE: The
group of items being held in reserve for possible future assignment to an
ISOLATION: Determining the
location of a failure to the extent possible.
ITEM: A general term used to
denote any product, system, material, part, subassembly, set, accessory, shop
replaceable assembly (SRA), Shop Replaceable Unit (SRU), Weapon Replaceable
Assembly (WRA), Line Replaceable Unit (LRU), etc.
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
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
LIFE PROFILE: A time-phased
description of the events and environments experienced by an item throughout
its life. Life begins with manufacture, continues during operational use
(during which the item has one or more mission profiles), and ends with final
expenditure or removal from the operational inventory.
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
LIFE UNITS: A measure of use
duration applicable to the item. Measures include time, cycles, distance,
rounds fired, attempts to operate, etc.
LOCALIZATION: Determining the
location of a failure to the extent possible, without using accessory test