A '''line-replaceable unit (LRU<ref>[http://www.e-publishing.af.mil/shared/media/epubs/PUBS/AF/23/23011002/020203/020203.pdf]</ref>)''' or, '''lowest replaceable unit'''{{fact|date=August 2012}}, or '''line-replaceable component''' (LRC) is a modular component of an [[fixed-wing aircraft|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>[http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?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. 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 are trypically assigned logistics control numbers (LCNs) or work unit codes (WUCs) to manage [[logistics]] operations.
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.<ref>[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>
