Line-replaceable unit: Difference between revisions

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{{Short description|Modular component designed to be replaced quickly at an operating ___location}}

{{refimprove|date=February 2008}}

A '''line-replaceable unit''' ('''LRU'''<ref>[http://www.e-publishing.af.mil/shared/media/epubs/PUBS/AF/23/23011002/020203/020203.pdf] {{webarchive |url=https://web.archive.org/web/20090704180412/http://www.e-publishing.af.mil/shared/media/epubs/PUBS/AF/23/23011002/020203/020203.pdf |date=July 4, 2009 }}</ref>), '''lower line-replaceable unit''' ('''LLRU'''),{{citation needed|date=August 2012}} '''line-replaceable component''' ('''LRC'''), or '''line-replaceable item''' ('''LRI''')<ref>[http://www.casa.gov.au/scripts/nc.dll?WCMS:PWA::pc=PC_93235#L Australian Government Civil Aviation Safety Authority, Aviation abbreviations and acronyms, Retrieved 11 July 2013]</ref> is a modular component of an [[airplane]],<ref>[http://adsabs.harvard.edu/abs/1985aifo.reptX....L A comparative evaluation of the reliability improvement in line replaceable unit<!-- Bot generated title -->]</ref> [[ship]] or [[spacecraft]]<ref>[httphttps://ieeexplore.ieee.org/xpldocument/freeabs_all.jsp4113049/;jsessionid=E294084DFFB5E3DDFB812A2192F5BC7A?arnumber=4113049 Welcome to IEEE Xplore 2.0: Line Replaceable Unit (LRU) Analysis in the Space Shuttle Orbiter Electrical Power System<!-- Bot generated title -->]</ref> (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]] or other auxiliary equipment. LRUs are typically assigned logistics control numbers (LCNs) or work unit codes (WUCs) to manage [[logistics]] 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.<ref>[https://web.archive.org/web/20080526105910/http://stinet.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA201577 A Cost Trade-Off Analysis of F-16 Line Replaceable Unit (LRU) Packaging Options<!-- Bot generated title -->]</ref>

LRUs are similar in nature to [[shop-replaceable unit|shop-replaceable units]] (SRUs), but rather than being component functions, represent complete functional units.

== Definition ==

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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:

<blockquote>An '''LRU''' is an essential support item which is removed and replaced at the UNITfield 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.</blockquote>

<blockquote>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.</blockquote>

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== 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 [[XLRCircular connector|cannon plugplugs]]s that can be removed and replaced (R&R) without tools. Specifications also define the supporting [[tool]]s necessary to remove and replace the unit. Many require no tools, or a standard-sized [[screwdriver#Blade types|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 [[fire|flammability]], unwanted radio emissions, resistance to damage from [[fungus]], [[static electricity]], [[heat]], [[pressure]], [[humidity]], [[condensation]] drips, [[oscillation|vibration]], [[radiation]], and other environmental measurements.

LRUs may be designed to [[ARINC]] 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]] 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]].<ref>"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." [http://www.defenselink.mil/contracts/contract.aspx?contractid=3521 United States Department of Defense Contracts, No. 615-07, May 21, 2007]</ref> On the [[International Space Station]], LRUs are referred to as [[Orbit-replaceable Replaceableunit|orbit-replaceable Unitunits]]s.

==See also==

* [[Aircraft maintenance]]

* [[Avionics]]

* [[Level of Repairrepair Analysisanalysis]]

* [[Maintenance, repair, and operations]]

* [[Spare part]]

* [[Shop-replaceable unit]]

* [[Field-replaceable unit]]

==References==

{{Reflist}}

7. https://apps.dtic.mil/sti/tr/pdf/ADA268674.pdf

[[Category:Aircraft components]]

[[Category:Military aviation]]