Line-replaceable unit
Encyclopedia
A line-replaceable unit (LRU) is a modular component of an airplane
, ship
or spacecraft
that is designed to be replaced quickly at an operating location. An LRU is usually a sealed unit such as a radio
or other auxiliary equipment. LRUs are sometimes described as "black box
es" despite the fact that they aren't necessarily black.
LRUs improve maintenance operations, because they can be stocked and replaced quickly from on-site inventory, restoring the system to service, while the failed (unserviceable) LRU is undergoing maintenance. Because they are modular, they also reduce system costs and increase quality, by centralizing development across different models of vehicles.
LRUs are designed to common specifications, with cannon plug
input/output interfaces. Specifications also define the tool
s necessary to remove and replace (R&R) the unit and the bulk and weight (they typically need to be transportable and fit through a door or hatchway). There are also requirements for flammability
, unwanted radio emissions, resistance to damage from fungus
, static electricity
, heat
, pressure
, humidity
, condensation
drips, vibration
, radiation
and other environmental measurements.
Many LRUs for commercial aircraft are designed according to ARINC
specifications, such as ARINC 404 and ARINC 600. LRUs are also defined by manufacturers like Airbus
and Boeing
and by various military organizations. In the military, electronic LRUs are typically designed to interface according to data bus standards such as MIL-STD-1553
. On the International Space Station
, LRUs are referred to as Orbit Replaceable Unit
s.
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...
, ship
Ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...
or spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
that is designed to be replaced quickly at an operating location. An LRU is usually a sealed unit such as a radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
or other auxiliary equipment. LRUs are sometimes described as "black box
Black box
A black box is a device, object, or system whose inner workings are unknown; only the input, transfer, and output are known characteristics.The term black box can also refer to:-In science and technology:*Black box theory, a philosophical theory...
es" despite the fact that they aren't necessarily black.
LRUs improve maintenance operations, because they can be stocked and replaced quickly from on-site inventory, restoring the system to service, while the failed (unserviceable) LRU is undergoing maintenance. Because they are modular, they also reduce system costs and increase quality, by centralizing development across different models of vehicles.
Definition and Specifications
While the term LRU has been in use for decades, MIL-PRF-49506, Notice 1 of 18 Jan 05, the Performance Spec for Logistics Management Information defines an LRU as:An LRU is an essential support item which is removed and replaced at the field level to restore the end item to an operational ready condition. Conversely, a non-LRU is a part, component, or assembly used in the repair of an LRU, when the LRU has failed and has been removed from the end item for repair.
LRUs are designed to common specifications, with cannon plug
XLR connector
The XLR connector is a style of electrical connector, primarily found on professional audio, video, and stage lighting equipment. The connectors are circular in design and have between 3 and 7 pins...
input/output interfaces. Specifications also define the tool
Tool
A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...
s necessary to remove and replace (R&R) the unit and the bulk and weight (they typically need to be transportable and fit through a door or hatchway). There are also requirements for flammability
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....
, unwanted radio emissions, resistance to damage from fungus
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
, static electricity
Static electricity
Static electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...
, heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
, pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
, humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
, condensation
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
drips, vibration
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
, radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
and other environmental measurements.
Many LRUs for commercial aircraft are designed according to ARINC
ARINC
Aeronautical Radio, Incorporated , established in 1929, is a major provider of transport communications and systems engineering solutions for eight industries: aviation, airports, defense, government, healthcare, networks, security, and transportation...
specifications, such as ARINC 404 and ARINC 600. LRUs are also defined by manufacturers like Airbus
Airbus
Airbus SAS is an aircraft manufacturing subsidiary of EADS, a European aerospace company. Based in Blagnac, France, surburb of Toulouse, and with significant activity across Europe, the company produces around half of the world's jet airliners....
and Boeing
Boeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
and by various military organizations. In the military, electronic LRUs are typically designed to interface according to data bus standards such as MIL-STD-1553
MIL-STD-1553
MIL-STD-1553 is a military standard published by the United States Department of Defense that defines the mechanical, electrical, and functional characteristics of a serial data bus. It was originally designed for use with military avionics, but has also become commonly used in spacecraft on-board...
. On the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
, LRUs are referred to as Orbit Replaceable Unit
Orbit Replaceable Unit
An Orbital Replaceable Unit is a modular component of spacecraft that can be replaced upon failure by a robot or by an Extra-Vehicular Activity. The Hubble Space Telescope was designed with 70 such parts. The electrical system of the International Space Station also has such subsystems that...
s.
See also
- Annex: Acronyms and abbreviations in avionics
- AvionicsAvionicsAvionics are electronic systems used on aircraft, artificial satellites and spacecraft.Avionic systems include communications, navigation, the display and management of multiple systems and the hundreds of systems that are fitted to aircraft to meet individual roles...
- Source, Maintenance, and Recoverability Code
- Spare partSpare partSpare Parts may also refer to:* Spare Parts , by Status Quo* Spare Parts is a Doctor Who audio drama.* Spare Parts , by Servotron* "Spare Parts" , by Bruce Springsteen* "Spare Parts"...
- Two-Level Maintenance
- Three-Level Maintenance
- Line-Replaceable Module (LRM)--commonly a circuit card component of a LRU designed to be repaired at the organizational Level (O-Level Maintenance).
- Shop-Replaceable Unit (SRU)--commonly a circuit card component of a LRU designed to be repaired at the field Level (at a backshop, known as I-Level Maintenance).