Line Replaceable Units Research Articles

The impact of counterfeit components and LRUs in the navy surface warfare supply chain: A systems dynamics approach

AbstractMicroelectronics integrity is a critical issue for many industries including the Department of Defense (DoD). The military systems the DoD operates are particularly vulnerable to counterfeiting, with potentially costly or even catastrophic consequences. Counterfeits, regardless of production intent (malign or ersatz), raise significant concerns for industry and the DoD because they often demonstrate operational performance shortcomings, have lower reliability, or make components or organizations more vulnerable to attack. This article uses a systems dynamics modeling approach to explore the economics of counterfeiting for a sample system, the interactions between counterfeiters and the US Navy supply chain, and the impacts of counterfeit surveillance and detection to address the question: Is it more effective to target detection efforts at the component level or at the Line Replaceable Units level? A case study of an engine control module for the LM2500 propulsion turbine used on US Navy Arleigh Burke class guided missile destroyer (DDG‐51) platforms is provided to demonstrate the approach.

Inline induction heating for high-pressure fuel-based testing applications

Induction heating offers numerous advantages over conventional methods for heating high-pressure fluids in hydraulic testing applications. It simplifies complex processes, mitigates the risks associated with high-pressure environments, and enhances overall safety. The design of an efficient induction heating system requires a clear understanding of its key components, including the resonant tank circuit, impedance matching and isolation stage, high-frequency inverter, driver circuitry, and controller. The configuration of the resonant circuit plays a crucial role in device ratings and control methods. To meet the demanding requirements of switching devices like IGBTs, the driver circuit must ensure high immunity to interferences and failure. Effective system design allows the heating circuit to operate close to resonant switching, minimizing switching losses and cooling requirements. This paper presents the design and development of a 4-kW induction heater specifically tailored for inline heating of aviation fuel under high pressure. The system aims to achieve a precise temperature profile for testing line-replaceable units (LRUs) used in aircraft. The design methodology encompasses the selection of the resonant tank circuit configuration, impedance matching and isolation stage, high-frequency inverter, driver circuitry, and control strategies. Through extensive simulations in LTspice and experimental measurements, power losses in different components of the power conversion circuits are assessed, and overall system efficiency is evaluated. The results demonstrate the proposed induction heating system’s remarkable energy efficiency, reduced switching losses, and improved reliability. Furthermore, a comprehensive comparison with existing designs and industry norms is presented, highlighting the distinct advantages of the proposed system in terms of cost-effectiveness, energy efficiency, material utilization, and processing time. This research contributes valuable insights into the design and optimization of induction heating systems for high-pressure fluid heating applications, providing a practical and efficient solution for the aviation industry.

Optimal design of line replaceable units

AbstractA line replaceable unit (LRU) is a collection of connected parts in a system that is replaced when any part of the LRU fails. Companies use LRUs as a mechanism to reduce downtime of systems following a failure. The design of LRUs determines how fast a replacement is performed, so a smart design reduces replacement and downtime cost. A firm must purchase/repair a LRU upon failure, and large LRUs are more expensive to purchase/repair. Hence, a firm seeks to design LRUs such that the average costs per time unit are minimized. We formalize this problem in a new model that captures how parts in a system are connected, and how they are disassembled from the system. Our model optimizes the design of LRUs such that the replacement (and downtime) costs and LRU purchase/repair costs are minimized. We present a set partitioning formulation for which we prove a rare result: the optimal solution is integer, despite a nonintegral feasible polyhedron. Second, we formulate our problem as a binary linear program (BLP). The article concludes by numerically comparing the computation times of both formulations and illustrates the effects of various parameters on the model's outcome.

Defect Trend Analysis for a Military Turbojet Engine: Case Studies

Turbojet engines are currently used for military application under training and combat modes. Their operation at extreme conditions often unscheduled with need based throttle excursions lead to high cyclic stresses on engine components and unusual demands on line replaceable units and accessories. As a result, a number of engines are forced for premature withdrawal from service affecting the flight schedule of the operator. This present paper presents the trend analysis of various defects encountered in a military turbojet engine and its accessories. This analysis will help in identifying the probable causes of the defects, time of engine withdrawal and whether they are of reoccurring nature or isolated cases so that corrective action can be initiated to avoid such snags in future.

METHODS FOR FORECASTING DEMAND IN REPAIRING AN AIRLINE’S REPAIRABLE LINE REPLACEABLE UNIT PARTS

Scattered failure frequency, variable and complex influencing factors, and a low accuracy in predicting inventory demand are characteristics of line replaceable unit (LRU) parts. Some high-priced repairable LRU (HR-LRU) parts have a considerable impact on the cost of aircraft spare parts.This study presents procedures to identify the optimal model for forecasting the demand for HR-LRU parts. First, a traditional prediction model, seven single measurement models, and four combined models were selected and used to predict failure data. Subsequently, evaluating indexes were selected for assessment to obtain the optimal model. Finally, we compared the actual and predicted values to verify the conclusions drawn during the previous evaluation step. The results indicated that, among the single models, the negative binomial regression model and the Holt-Winters model were most suitable for HR-LRU parts. The SSE (sum of squares error) and MAE (mean absolute error) of the negative binomial regression were the lowest at 118.4114 and 1.97352 respectively, and the Holt-Winters model’s MAE was the lowest at 1. 13270. The IOWA operator prediction model and the error reciprocal variable weight combination method produced predictions closest to the actual values among the combined models. In addition to constructing a set of processes to prediction, we also discuss the fit of different methods, the reasons for the change in the guaranteed rate, and the reasons for the occurrence of special years. We also compare the similarities and differences between this article and other papers.

Software for Testability Analysis of Aviation Systems

This paper describes models, methods and software tool for testability analysis of aviation systems. It comprises analytical and programing aspects of calculations of main testability, reliability and availability indices. It presents general description of the software, XML schema of input data and technique of their mapping to the database structure. The procedure for generating the initial data for testability analysis based on the line replaceable units failure modes report is described. Fault tree model for analysis of the built-in test conformity is suggested. Markov models have been created for analyzing reliability and availability, taking into account the features of the built-in test and the specifics of the aircraft operation. An approach to the construction of trends in the operative availability of aviation systems in the inter-maintenance interval is proposed.

Research on LRU Hierarchy based on Optimal Granularity Level

In order to improve the convenience of replacing faulty equipment on the route and realize LRU(Line Replaceable Unit) level planning reasonably and effectively, a LRU hierarchical division method based on optimal granularity level is proposed. Based on the analysis of the relationship between the components in the product structure, the design structure matrix theory is introduced to construct the comprehensive relationship matrix, which quantifies the relationship between the components from two levels of function and structure. By defining modularization index, combining with the hierarchical traversal of product structure tree, the optimal granularity level is calculated. This method can provide a division scheme based on hierarchical factors for LRU planning and provide support for getting more optimized LRU planning and design.

Research on the Plan of Plane Line Replaceable Units Based on FSMC Model

The line replaceable unit (LRU) is a direct carrier of the fighter’s field replacement and maintenance strategy. It is reasonably and accurately divided into modules, which can quickly locate the fault location, reduce maintenance support time, and improve the efficiency of maintenance support Improve combat effectiveness. Aiming at the problem of the LRU division method in the aircraft design stage, this paper proposes an FSMC aircraft LRU division method based on function-structure-maintainability-coupling, comprehensively uses fuzzy clustering and other methods to evaluate and analyse the LRU division scheme, and compare different LRU schemes Use availability of the aircraft to perform simulation analysis. The research results show that the established on-site replaceable unit evaluation model can solve the problem of fighter aircraft LRU division schemes in the context of actual combat, and provide model support and empirical reference for further research on aircraft LRU division design research.

Spare parts allocation of amphibious aircraft based on hybrid two-level repair

In this paper, a hybrid two-level inventory allocation method based on multi-echelon technique for recoverable item control (METRIC) was applied to the spare parts allocation of amphibious aircraft. Firstly, the principle of the spare parts inventory configuration model for amphibious aircraft based on hybrid two-level repair was expounded. The mathematical model was established with maintenance cost as objective function and availability and volume of spare parts as constraints. Secondly, marginal analysis was used to help allocate spare parts, the process of solving the mathematical model was discussed, and the calculation formulas of the quantities involved were briefly stated. Finally, with the line replaceable units of landing gear as the research object, the spare parts inventory allocation of an amphibious aircraft was solved according to the method proposed in this paper. This paper provides an approach to allocate spare parts of amphibious aircraft.

Dynamic Safety Assessment of Aircraft Mechanism using Extremum Framework with Fault Tree Analysis

In this paper, a hybrid two-level inventory allocation method based on multi-echelon technique for recoverable item control (METRIC) was applied to the spare parts allocation of amphibious aircraft. Firstly, the principle of the spare parts inventory configuration model of amphibious aircraft based on hybrid two-level repair was expounded. The mathematical model was established with maintenance cost as objective function and availability and volume of spare parts as constraints. Secondly, marginal analysis was used to help allocate spare parts, the process of solving the mathematical model was discussed, and the calculation formulas of the quantities involved were briefly stated. Finally, with the line replaceable units of landing gear as the research object, the spare parts inventory allocation of a amphibious aircraft was solved according to the method proposed in this paper. This paper provides an approach to allocate spare parts of amphibious aircraft.

Real-Time Maintenance Optimization Considering Health Monitoring and Additive Manufacturing

Prognostics Health Management (PHM) and Integrated Vehicle Health Management (IVHM) are extensive areas of research. Whereas a lot of work has been done in diagnostics and prognostics, economic viability is an important consideration. The availability of aircraft in the aerospace sector is a critical factor. Thus, cost and downtime are the main parameters to assess the impact of IVHM. Additionally, new repair technologies, such as additive manufacturing (AM), have the potential to become standard repair procedures, complementing IVHM, and its viability also has to be assessed. However, to accurately study the impact of these factors, the characteristics of aerospace maintenance have to be taken into account. Several approaches are followed in aircraft maintenance, depending on cost, downtime and aircraft availability constraints. For instance, some parts can be repaired on the ground and assembled again on the same aircraft, while single Line Replaceable Units (LRUs) need to be removed, replaced and later repaired in the workshop without affecting the availability of the aircraft. With the gradual introduction of IVHM, the viability of any new IVHM technology needs to be assessed.This paper describes an extensive cost and downtime model to take into account all these scenarios, including the impact of using different types of IVHM systems. The impact of IVHM and new repair technologies is discussed comparing maintenance cost and downtime of parts of LRUs and parts repaired when the aircraft is on the ground.Secondly, a real-time maintenance case study based on IVHM, a cost and downtime model and additive manufacturing is presented. This application allows the optimization of maintenance activities by updating the available resources and their corresponding cost and time, along with the actual prediction of the Remaining Useful Life (RUL) using a health monitoring system, instead of depending on historical component/sub-system failure probabilities.

A System-Level Failure Propagation Detectability Using ANFIS for an Aircraft Electrical Power System

The Electrical Power System (EPS) in an aircraft is designed to interact extensively with other systems. With a growing trend towards more electric aircraft, the complexity of interactions between the EPS and other systems has grown. This has resulted in an increased necessity of implementing health monitoring methods like diagnosis and prognosis of the EPS at the systems level. This paper focuses on developing a diagnostic algorithm for the EPS to detect and isolate faults and their root causes that occur at the Line Replaceable Units (LRUs) connecting with aircraft systems like the engine and the fuel system. This paper aims to achieve this in two steps: (i) developing an EPS digital twin and presenting the simulation results for both healthy and fault scenarios, (ii) developing an Adaptive Neuro-Fuzzy Inference System (ANFIS) monitor to detect faults in the EPS. The results from the ANFIS monitor are processed in two methods: (i) a crisp boundary approach, and (ii) a fuzzy boundary approach. The former approach has a poor misclassification rate; hence the latter method is chosen to combine with causal reasoning for isolating root causes of these interacting faults. The results from both these methods are presented through examples in this paper.

Performance Evaluation of Wireless Protocols for Avionics Wireless Network

Ever-increasing demand for higher bandwidth and data rate for communication between line replaceable units in an aircraft is forcing aircraft manufacturers to turn toward alternative technologies, including wireless to replace the existing network of wires, for future generation aircraft. Wireless technology can meet most of the challenges of modern avionics systems, apart from significantly reducing the weight due to wires and associated hardware, with proper selection of technology. Boeing and Airbus have started using wireless technology for in-flight entertainment systems. Wireless Avionics Intra-Communication (WAIC) is expected to pave the way for use of wireless technology in avionics. One of the crucial factors in introducing a wireless network in an aircraft for flight critical operations is identifying a suitable wireless protocol that meets the avionics safety requirements. This paper aims to evaluate different commercial off-the-shelf wireless protocols for introducing an avionics wireless network (AWN) in an aircraft. The comparison is carried out on the basis of various parameters, such as transmission time, coding efficiency, throughput, range, number of nodes in AWN, energy consumption, and security. Based on the comparison and simulation, suitable protocols for WAIC have been identified.

A Method for Dividing Line Replaceable Unit

The problem of dividing the line replaceable unit (LRU) is one of the urgent problems to be solved in the RMS field in recent years. This paper proposes a method of line replaceable unit division, based on actual needs, to study the need of LRU division trade-off. On this basis, the indicators and parameters of LRU division trade-offs are studied to realize the scientific division of LRU, which provides support for product reliability, maintainability, supportability and test engineering design and analysis.

Capacity assignment in repair shops with high material uncertainty

We consider a group of identical systems, each consisting of multiple Line Replaceable Units (LRUs) that fail according to a Poisson process. A failed LRU is replaced by a ready-for-use one from a single stock point and, if not available, a backorder cost is incurred per unit of time. The failed LRU is returned to a repair shop, where it is inspected to identify which Shop Replaceable Units (SRUs) caused the failure, and is repaired by replacing the failed SRUs. After repair the LRU is ready-for-use again. Both the LRUs and SRUs are controlled by base stock policies. The repair shop is modeled as a two-stage service process consisting of an inspection and a repair phase. Inspection and repair are executed by one group of repairmen. The repair times depend on the time that elapses between inspection and the repair of a part. We model the total repair capacity as a single server and we compare policies that, based on the repair workload in the repair shop, give priority to either inspection or repair of parts. We suggest two approaches to set the SRU base stock levels, and simulate the system for multiple combinations of the repair workload threshold and predetermined vectors of SRU base stock levels. Based on the simulation results, the LRU base stock levels are optimized. We study a representative setting in which the repair shop faces a high material uncertainty, under different scenarios. We show that a scenario in which we maximize the SRU job completeness, combined with a repair priority policy (in which repair of jobs takes precedence over inspection of jobs) leads to the lowest total costs.

VHDL Design of ARINC 429 Bus Protocol

ARINC 429 is a data transfer standard for aircraft avionics which is also known as the Mark 33 DITS Specification (Digital Information Transfer System). It makes use of self-clocking and self-synchronizing techniques. ARINC-429 bus interface is used as a controlling function. It is a two-wire point-to-point serial data bus for control communications in avionics. The bus operates at the speed of 100kb/sec; the ARINC429 is developed to provide interchangeability and interoperability of line replaceable units (LRUs) in commercial aircraft. File transfer of ARINC 429 protocol is bit oriented, handshake between the transmitter and receiver units is necessary at the initial condition. Predefined codes are sent from the source initiates communication with the receiver to determine compatibility between the units required for successful transmission. FPGA implementation of bus protocol can be done , for this purpose SRAM memory is used to sort the data into the buffer and make use of the information whenever needed. In order to enhance the security during transmission converters and key can be used. It is one of the modern techniques used in aircrafts and military. Keywords: ARNIC429, LRU, independent transmitter and receiver Cite this Article J. Joshua Bapu, I.J. Divya Prasanna, M. Sheela Merlin . VHDL Design of ARINC 429 Bus Protocol. Journal of Aerospace Engineering and Technology. 2016; 6(2): 21–27p.

Biomechanical analysis of accurately and carefully placing an aerospace avionics box in restricted space

The design of a spacecraft has many trade-offs to reduce its mass, which typically result in reduced work space for the installation of Line Replaceable Units (LRU). One common LRU in aerospace vehicles is the avionics box found in the space shuttle. To prevent damage to cold plates, the installation of these boxes requires designing for accurate and careful placement; yet there are no standards to follow nor studies to consider for designers concerning human limitations for installing boxes accurately and carefully. In the literature, there are an abundance of lifting studies; however, there are only a few studies that have placed a box in restricted space or on a target as a constraint. Of those studies, only three have looked at the biomechanics, and none of those studies have looked at factors affecting the Placement Control (accurate and careful placement) of a box on a target in restricted or unrestricted space. Thus, the focus of this study is to determine the biomechanical stresses and the human performance metrics for Placement Control (accurate and careful placement) of a box on target in restricted space.

The Impact of a Wet <inline-formula> <tex-math notation="LaTeX">$S$ </tex-math> </inline-formula>-Band Radome on Dual-Polarized Phased-Array Radar System Performance

This paper discusses the impact of a wet flat radome on the performance of a line replaceable unit active phased-array antenna developed for a dual-polarized phased-array weather radar. Water formations, such as film and droplets, were fully characterized over flat and curved radome surfaces using an analytical model as a function of the precipitation rate. Numerical simulations and experimental results validated the proposed analytical model. An active dual-polarized phased-array of $8\times 2$ elements was used to evaluate the degradation of the cross-polarization component as well as the mismatch and the phase of scanned antenna radiation patterns for vertical and horizontal polarizations. In addition, a radome panel of an $S$ -band weather radar (WSR-88D) was characterized in the far field using a single radio-frequency probe. It is demonstrated that even at the $S$ -band, the water formation on the radome affects both copolarization and cross-polarization components, degrading the overall performance of the dual-polarized radar system under rain conditions.

The SOFIA Telescope in Full Operation

The SOFIA telescope is a 2.5[Formula: see text]m class Cassegrain telescope with Nasmyth focus. It is the largest telescope ever integrated into an aircraft. The telescope is exposed to the stratospheric environment during the observations and the fact that the telescope’s foundation, which is a Boeing 747 SP, is vibrating and moving in all degrees of freedom (DoF) requires a highly specialized and sophisticated design. Based on the telescope of its predecessor, the Kuiper Airborne Observatory (KAO), the SOFIA telescope design had to evolve to accommodate a telescope 2.5 times the size of KAO. In several hundred successful observation flights, the telescope proved that it performs not only as specified, but is also extremely reliable. Nevertheless, the telescope’s software and hardware are continuously upgraded to optimize its performance without interfering with the observation schedules to reach even more ambitious image size and pointing jitter goals to enable additional science cases. In addition, manufacturing of the line-replaceable units is in process to ensure that the SOFIA telescope can perform without any major interruptions for the envisioned 20 year lifetime. Some of the main features of the SOFIA telescope are its suspension assembly (SUA), which decouples the telescope from SOFIA’s fuselage with air springs and a spherical oil bearing, the extremely stiff Nasmyth tube (NT), which connects cavity and cabin mounted components of the dumbbell design, and the Secondary Mirror Assembly (SMA), which is used for chopping and fast pointing corrections. This paper aims to give an overview of these and all other major telescope subsystems in operation today. In addition, some of the upgrades, either implemented recently or slated for implementation shortly, are introduced.

Cleaning State of the Loop Case for Optical Crystal Module in Final Optics Assembly

In order to solve the online clean maintenance problem of the optical frequency-doubling crystal module in the final optics assembly, a crystal loop case is developed for better controlling the clean maintenance process. The study presents a detailed research on the cleanliness of the crystal loop case during the online maintenance process and the installation sequence of the crystal modules in the crystal. It first established a fluid simulation model of the crystal loop case system according to the online maintenance process and then analyzed the isolation effect of inlet velocity on the polluted air in view of the cleaning effect of the crystal loop case. Based on the simulation principle of gas–solid two-phase flow and the tracking results of the solid particle contamination, the range of air inflow is given for achieving the best cleaning status of the loop case. The optimal sequence of crystal module is explicit for its installation in the crystal loop case of frequency-doubling crystal module. The experimental setup has been built to examine the cleaning state of the crystal loop case, and the simulation result has been validated. The research on the cleanliness of crystal loop case can provide a useful reference for the ultra-clean manufacturing of line replaceable units and the closed loop control of cleaning in high-power laser facility.