- A -
ACCESSIBILITY: A measure of the relative
ease of admission to the various areas of an item for the purpose of operation
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
ADMINISTRATIVE TIME: That element of delay time, not
included in the supply delay time.
AFFORDABILITY: Affordability 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.
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.
ANTHROPOMETRICS: Quantitative 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 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.)
- B -
BUILT-IN-TEST (BIT): An integral capability of the mission 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
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
- C -
CALIBRATION: A comparison of a measuring device with a known standard and a
subsequent adjustment to eliminate any differences. Not to be confused with
CHECKOUT: Tests or observations of an item to determine its condition or
CHECKOUT TIME: That element of maintenance time during which performance of
an item is verified to be a specified condition.
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 SD-2 or the Federal Acquisition
Regulation, Parts 6, 10, 11,
12 and 14, for a complete definition and
COMMERCIAL-OFF-THE-SHELF (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 item.
COMPUTER-AIDED DESIGN (CAD): A process which uses a computer system to
assist in the creation, modification, verification, and display of a
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 Government.
CORRECTIVE ACTION: A documented design, process, procedure, or materials
change implemented and validated to correct the cause of failure or design
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.
- D -
DATA ITEM DESCRIPTION (DID): A Government form used to define and describe
the written outputs required from a contractor.
DELAY TIME: That element of downtime during which no maintenance is being
accomplished on the item because of either supply or administrative delay.
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")
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. (Item state during a mission includes the combined effects of the
mission-related system R & M parameters but excludes non-mission time; see
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
DETECTABLE FAILURE: Failures at the component, equipment, subsystem, or
system (product) level that can lie 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,
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
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
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
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.
DOWNTIME: That element of time during which an item is in an operational
inventory but is not in condition to perform its required function.
- E -
ELEMENT MAINTENANCE ACTION: A unit of work into which a maintenance
activity may be broken down at a given indenture level.
EQUIPMENT: A general term designating an item or group of items capable of
performing a complete function.
- F -
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
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 MECHANISM: The physical, chemical, electrical, thermal or other
process which results in failure.
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, 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 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.
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,
FAULT DETECTION (FD): A process which discovers the existence of
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.
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.
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
- G -
GOVERNMENT-FURNISHED EQUIPMENT (GFE): An item provided for inclusion in or
use with a producer service being procured by the Government.
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.
- H -
HUMAN ENGINEERING (HE): The application of scientific knowledge to the
design of items to achieve effective user-system integration (man-machine
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 performance evaluation.
- I -
INACTIVE TIME: That time during which an item is in reserve. (In an
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.
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
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
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 taken.
INTERCHANGE: Removing the item that is to be replaced, and installing the
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.
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 unit.
ISOLATION: Determining the location of a failure to the extent possible, by
the use of accessory equipment.