A line-replaceable unit (LRU), lower line-replaceable unit (LLRU), line-replaceable component (LRC), or line-replaceable item (LRI) is a modular component of an
airplane
An airplane or aeroplane (informally plane) is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, propeller, or rocket engine. Airplanes come in a variety of sizes, shapes, and wing configurations. The broad spe ...
,
ship
A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished ...
or
spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
(or any other manufactured device) that is designed to be replaced quickly at an operating location (1st line). The different lines (distances) are essential for logistics planning and operation. An LRU is usually a sealed unit such as a
radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...
or other auxiliary equipment. LRUs are typically assigned logistics control numbers (LCNs) or work unit codes (WUCs) to manage
logistics
Logistics is generally the detailed organization and implementation of a complex operation. In a general business sense, logistics manages the flow of goods between the point of origin and the point of consumption to meet the requirements of ...
operations.
LRUs can improve maintenance operations, because they can be stocked and replaced quickly from distributed nearby on-site inventories (sometimes mobile storage), restoring the mobile systems to service, while the failed (unserviceable) LRU is undergoing complicated repair and overhaul actions in other support locations (lines). Because of their modularity, LRUs also can contribute reducing system costs and increase quality, by centralizing development across different models of vehicles.
LRUs are similar in nature to
shop-replaceable units (SRUs), but rather than being component functions, represent complete functional units.
Definition
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 / LLRU, when the LRU has failed and has been removed from the end item for repair.
An LLRU is part of an LRU, and which can be removed and replaced at the field level to restore its LRU to an operational ready condition. As an LRU is considered the 'parent', the LLRU is considered a 'child'. An LLRU can also be a child of a child--that is, an LLRU being a component of a higher-level LLRU. However, there is no hierarchy difference between child levels; the only hierarchical separation is parent versus child.
Specifications
LRUs are designed to specifications to assure that they can be interchanged, especially if they are from different manufacturers. Usually a class of LRUs will have coordinated environmental specifications (i.e. temperature, condensation, etc.). However, each particular LRU will also have detailed specifications describing its function, tray size, tray connectors, attachment points, weight ranges, etc. It is common for LRU trays to have standardized connections for rapid mounting, cooling air, power, and grounding. The mounting hardware is often manually removable standard-screw-detent quick-release fittings. Front-mounted electrical connectors are often jacks for ring-locked
cannon plugs that can be removed and replaced (R&R) without tools. Specifications also define the supporting
tool
A tool is an object that can extend an individual's ability to modify features of the surrounding environment or help them accomplish a particular task. Although many animals use simple tools, only human beings, whose use of stone tools dates ba ...
s necessary to remove and replace the unit. Many require no tools, or a standard-sized
Frearson screwdriver. Frearson is specified for some vehicles and many marine systems because Frearson screws keep their mating screwdriver from camming out, and the same screwdriver can be used on many sizes of screws. Most LRUs also have handles, and specific requirements for their bulk and weight. LRUs typically need to be "transportable" and fit through a door or hatchway. There are also requirements for
flammability
A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...
, unwanted radio emissions, resistance to damage from
fungus
A fungus ( : fungi or funguses) is any member of the 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, separately from th ...
,
static electricity
Static electricity is an imbalance of electric charges within or on the surface of a material or between materials. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is na ...
,
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
,
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
,
humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Humidity depe ...
,
condensation
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to ...
drips,
vibration
Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic function, periodic, such as the motion of a pendulum ...
,
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
, and other environmental measurements.
LRUs may be designed to
ARINC
Aeronautical Radio, Incorporated (ARINC), established in 1929, was a major provider of transport communications and systems engineering solutions for eight industries: aviation, airports, defense, government, healthcare, networks, security, and t ...
700-series standards. The form factor of LRUs comply to ARINC Standards,
ARINC 404 and
ARINC 600. LRUs are also defined by manufacturers like
Airbus
Airbus SE (; ; ; ) is a European Multinational corporation, multinational aerospace corporation. Airbus designs, manufactures and sells civil and military aerospace manufacturer, aerospace products worldwide and manufactures aircraft througho ...
and
Boeing
The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and product ...
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 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 as an avionic data bus for use with ...
.
["The B-52H Integrated Weapon Interface Unit (IWIU) program is a newly developed Line-Replaceable Unit (LRU) which will replace the current 1980s-developed LRUs which are becoming unsupportable. The LRUs currently installed in the Stub Pylon / Heavy Stores Adapter Beam (SP/HSAB) provide the command and control link between the B-52H Offensive Avionics System and all “smart” MIL-STD 1760 current and future weapons carried on the B-52H.]
United States Department of Defense Contracts, No. 615-07, May 21, 2007
/ref> On the International Space Station
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
, LRUs are referred to as Orbit Replaceable Unit
An orbital replacement unit or orbital replaceable unit is a modular component of spacecraft that can be replaced upon failure either by robot or by extravehicular activity. The Hubble Space Telescope (HST) was designed with 70 such parts, includ ...
s.
See also
* Aircraft maintenance
Aircraft maintenance is the performance of tasks required to ensure the continuing airworthiness of an aircraft or aircraft part, including overhaul, inspection, replacement, defect rectification, and the embodiment of modifications, compliance w ...
* Avionics
Avionics (a blend word, blend of ''aviation'' and ''electronics'') are the Electronics, electronic systems used on aircraft. Avionic systems include communications, Air navigation, navigation, the display and management of multiple systems, ...
* Level of Repair Analysis
Level of Repair Analysis (LORA) is used as an analytical methodology used to determine where an item will be replaced, repaired, or discarded based on cost considerations and operational readiness requirements. For a complex engineering system co ...
* Maintenance, repair, and operations
The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, and residential install ...
* Spare part
A spare part, spare, service part, repair part, or replacement part, is an interchangeable part that is kept in an inventory and used for the repair or refurbishment of defective equipment/units. Spare parts are an important feature of logistic ...
* Shop-replaceable unit
A shop-replaceable unit (SRU) or shop-replaceable component (SRC) is a modular component of an airplane, ship or spacecraft that is designed to be replaced by a technician at a backshop. Repair at backshops is known as field-level maintenance o ...
* Field-replaceable unit
A field-replaceable unit (FRU) is a printed circuit board, part, or assembly that can be quickly and easily removed from a computer or other piece of electronic equipment, and replaced by the user or a technician without having to send the entire p ...
References
{{Reflist
Aircraft components
Military aviation
Military maintenance