Line-replaceable unit

A line replaceable unit (LRU) is a complex component of an airplane, [ [http://adsabs.harvard.edu/abs/1985aifo.reptX....L A comparative evaluation of the reliability improvement in line replaceable unit ] ] ship or spacecraft [ [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 ] ] that is designed to be replaced quickly at the flightline or airport ramp area. An LRU is a black box (sealed unit), such as a radio or other auxiliary equipment. An LRU is also known as a line replaceable module (LRM) or shop replaceable unit (SRU). [ [http://www.almc.army.mil/alog/issues/Mar-Apr98/ms264.htm Coping With Obsolete Components ] ]

LRUs speed up repair, because they can be stocked and replaced quickly from inventory, restoring the larger system to service. They also reduce the cost of systems, and increase the quality, by spreading development costs of the type of unit over different models of vehicles. [ [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 ] ] Although an LRU is called a "black box" because its internal design is immaterial to the end user, the box itself is often painted gray in color.

LRUs are designed to common specifications. These specifications define the inputs and outputs with simple twist-on/twist-off cannon plug-type connectors. They also define the tools required to replace the unit (usually nothing more than a #2 Phillips-head screwdriver) and the bulk and weight (they typically need to be carried by one person and fit through a door, if possible). 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. ARINC (Aeronautical Radio Incorporated) is a company owned by a number of airlines that sells specifications and designates standards. LRUs are also defined by manufacturers like Airbus and Boeing and by various military organizations. Military LRUs are typically designed to interface according to data bus standards such as MIL-STD-1553. ["The B-52H Integrated Weapon Interface Unit (IWIU) program is a newly developed Line Replaceable Unit (LRU) which will replace the current 1980s developed LRU’s which are becoming unsupportable. The LRU’s 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] ]

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