Line-replaceable unit

Last updated

A line-replaceable unit (LRU [1] ), lower line-replaceable unit (LLRU),[ citation needed ]line-replaceable component (LRC), or line-replaceable item (LRI) [2] is a modular component of an airplane, [3] ship or spacecraft [4] (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.

Contents

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. [5]

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 tools 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, unwanted radio emissions, resistance to damage from fungus, static electricity, heat, pressure, humidity, condensation drips, 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. [6] On the International Space Station, LRUs are referred to as Orbit Replaceable Units.

See also

Related Research Articles

<span class="mw-page-title-main">Bus (computing)</span> System that transfers data between components within a computer

In computer architecture, a bus is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components and software, including communication protocols.

<span class="mw-page-title-main">Work breakdown structure</span> A deliverable-orientated breakdown of a project into smaller components.

A work-breakdown structure (WBS) in project management and systems engineering is a deliverable-oriented breakdown of a project into smaller components. A work breakdown structure is a key project deliverable that organizes the team's work into manageable sections. The Project Management Body of Knowledge defines the work-breakdown structure as a "hierarchical decomposition of the total scope of work to be carried out by the project team to accomplish the project objectives and create the required deliverables."

<span class="mw-page-title-main">Screwdriver</span> Hand-tool

A screwdriver is a tool, manual or powered, used for turning screws. A typical simple screwdriver has a handle and a shaft, ending in a tip the user puts into the screw head before turning the handle. This form of the screwdriver has been replaced in many workplaces and homes with a more modern and versatile tool, a power drill, as they are quicker, easier, and can also drill holes. The shaft is usually made of tough steel to resist bending or twisting. The tip may be hardened to resist wear, treated with a dark tip coating for improved visual contrast between tip and screw—or ridged or treated for additional 'grip'. Handles are typically wood, metal, or plastic and usually hexagonal, square, or oval in cross-section to improve grip and prevent the tool from rolling when set down. Some manual screwdrivers have interchangeable tips that fit into a socket on the end of the shaft and are held in mechanically or magnetically. These often have a hollow handle that contains various types and sizes of tips, and a reversible ratchet action that allows multiple full turns without repositioning the tip or the user's hand.

MIL-STD-1750A or 1750A is the formal definition of a 16-bit computer instruction set architecture (ISA), including both required and optional components, as described by the military standard document MIL-STD-1750A (1980). Since August 1996, it has been inactive for new designs.

A vehicle bus is a specialized internal communications network that interconnects components inside a vehicle. In electronics, a bus is simply a device that connects multiple electrical or electronic devices together. Special requirements for vehicle control such as assurance of message delivery, of non-conflicting messages, of minimum time of delivery, of low cost, and of EMF noise resilience, as well as redundant routing and other characteristics mandate the use of less common networking protocols. Protocols include Controller Area Network (CAN), Local Interconnect Network (LIN) and others. Conventional computer networking technologies are rarely used, except in aircraft, where implementations of the ARINC 664 such as the Avionics Full-Duplex Switched Ethernet are used. Aircraft that use AFDX include the B787, the A400M and the A380. Trains commonly use Ethernet Consist Network (ECN). All cars sold in the United States since 1996 are required to have an On-Board Diagnostics connector, for access to the car's electronic controllers.

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 transportation. ARINC had installed computer data networks in police cars and railroad cars and also maintains the standards for line-replaceable units.

Reliability engineering is a sub-discipline of systems engineering that emphasizes the ability of equipment to function without failure. Reliability describes the ability of a system or component to function under stated conditions for a specified period of time. Reliability is closely related to availability, which is typically described as the ability of a component or system to function at a specified moment or interval of time.

A United States defense standard, often called a military standard, "MIL-STD", "MIL-SPEC", or (informally) "MilSpecs", is used to help achieve standardization objectives by the U.S. Department of Defense.

Integrated logistic support (ILS) is a technology in the system engineering to lower a product life cycle cost and decrease demand for logistics by the maintenance system optimization to ease the product support. Although originally developed for military purposes, it is also widely used in commercial customer service organisations.

Environmental stress screening (ESS) refers to the process of exposing a newly manufactured or repaired product or component to stresses such as thermal cycling and vibration in order to force latent defects to manifest themselves by permanent or catastrophic failure during the screening process. The surviving population, upon completion of screening, can be assumed to have a higher reliability than a similar unscreened population.

ARINC 429, "Mark33 Digital Information Transfer System (DITS)," is also known as the Aeronautical Radio INC. (ARINC) technical standard for the predominant avionics data bus used on most higher-end commercial and transport aircraft. It defines the physical and electrical interfaces of a two-wire data bus and a data protocol to support an aircraft's avionics local area network.

A rugged computer or ruggedized computer is a computer specifically designed to operate reliably in harsh usage environments and conditions, such as strong vibrations, extreme temperatures and wet or dusty conditions. They are designed from inception for the type of rough use typified by these conditions, not just in the external housing but in the internal components and cooling arrangements as well.

ARINC 708 is a specification for airborne pulse Doppler weather radar systems primarily found on commercial aircraft.

Logistics Support Analysis (LSA) is a structured approach to increase efficiency of maintenance and reduces the cost of providing support by preplanning all aspects of Integrated Logistics Support. A successful LSA will define those support requirements that are ideal for the system design.

ARINC 826 is a protocol for avionic data loading over the Controller Area Network (CAN) as internationally standardized in ISO 11898-1. It allows Loadable Software Aircraft Parts to be loaded in a verifiable and secure manner to avionics Line Replaceable Units (LRUs) and Line Replaceable Modules (LRMs) using CAN.

<span class="mw-page-title-main">U.S. Military connector specifications</span>

Electrical or fiber-optic connectors used by U.S. Department of Defense were originally developed in the 1930s for severe aeronautical and tactical service applications, and the Type "AN" (Army-Navy) series set the standard for modern military circular connectors. These connectors, and their evolutionary derivatives, are often called Military Standard, "MIL-STD", or (informally) "MIL-SPEC" or sometimes "MS" connectors. They are now used in aerospace, industrial, marine, and even automotive commercial applications.

<span class="mw-page-title-main">Warner Robins Air Logistics Complex</span> Military unit

The Warner Robins Air Logistics Complex (WR-ALC), through about 7,000 employees at Robins Air Force Base, Georgia, provides depot maintenance, engineering support and software development to major weapon systems [F-15, C-5, C-130, C-17 and Special Operations Forces (SOF) aircraft]. The Complex achieves command objectives providing a capability/capacity to support peacetime maintenance requirements, wartime emergency demands, aircraft battle damage repair and a ready source of maintenance of critical items.

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 logistics engineering and supply chain management, often comprising dedicated spare parts management systems.

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 or intermediate-level (I-level) maintenance.

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 containing thousands of assemblies, sub-assemblies, components, organized into several levels of indenture and with a number of possible repair decisions, LORA seeks to determine an optimal provision of repair and maintenance facilities to minimize overall system life-cycle costs.

References

  1. Archived July 4, 2009, at the Wayback Machine
  2. Australian Government Civil Aviation Safety Authority, Aviation abbreviations and acronyms, Retrieved 11 July 2013
  3. A comparative evaluation of the reliability improvement in line replaceable unit
  4. Welcome to IEEE Xplore 2.0: Line Replaceable Unit (LRU) Analysis in the Space Shuttle Orbiter Electrical Power System
  5. A Cost Trade-Off Analysis of F-16 Line Replaceable Unit (LRU) Packaging Options
  6. "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