Airline replaceable unit determination method based on maintainability and economy
By using a maintainability- and economical approach, combined with qualitative and quantitative assessments, the problem of unreasonable LRU allocation was solved, achieving reasonable allocation and optimization, and improving maintenance efficiency and aircraft reliability.
Patent Information
- Application Number
- CN202511718173.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-21
- Publication Date
- 2026-02-27
AI Technical Summary
In the existing technology, the hierarchical classification of Aircraft Line Replaceable Units (LRUs) is unreasonable, resulting in frequent changes, lack of quantitative basis, reliance on engineering experience, and impact on maintenance costs and efficiency.
By adopting a maintainability and economy-based approach, functional partitioning, qualitative and quantitative assessments, combined with FMEA and MMEL, MTTR and DMC are calculated, and a comprehensive trade-off is made to determine the reasonable partitioning of LRUs.
This approach achieves rationality and optimization in LRU partitioning, reduces design iterations, improves maintenance efficiency and aircraft reliability, and lowers maintenance costs.
Smart Images
Figure CN121581840A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of aircraft maintainability analysis, and particularly relates to a method for determining aircraft line replaceable unit based on maintainability and economy. BACKGROUND
[0002] Line replaceable unit (LRU) refers to a unit (including equipment, assembly, component or part, etc.) that can be integrally disassembled and replaced during aircraft line maintenance, also known as field replaceable unit. During aircraft design, most aircraft assemblies are considered to be installed on the aircraft in the form of standard modules, such as landing gear control unit, flight control computer, flight data recorder, etc., so that maintenance personnel can complete the replacement of faulty LRUs in a short time during line maintenance and maintenance, thereby improving the efficiency of aircraft maintenance.
[0003] During the determination of LRU items, the division of LRU levels should also be fully considered: the higher the LRU division level, the higher the replacement or repair cost, the higher the requirement for tools and equipment, the higher the maintenance cost, and the more the aircraft release restrictions; the lower the LRU division level, although the replacement or repair cost is reduced, but it will cause the design complexity and technical difficulty to increase, the maintenance personnel to have a complex troubleshooting process, the aircraft to have an increased parking time, and the mission reliability to be reduced. Therefore, when seeking to determine the best LRU item, attention should be paid to the division of LRU levels, which can effectively control the economic indicators of "direct maintenance cost" and "aircraft inventory and management cost", greatly save the maintenance time, reduce the maintainability cost, and improve the aircraft mission reliability.
[0004] Currently, the domestic mainstream civil aircraft manufacturers all pay great attention to the division of LRU, and have researched the principles of LRU division, formulated a series of requirements, and continuously applied and optimized them in the type. However, there are still some outstanding problems, such as: the rationality of the division is insufficient, resulting in frequent changes in the later stage, so that large-scale modification and improvement are still being made after delivery to the customer; the division method has no unified standard and method, and most of them still rely on experience as the main method; the division level is not optimal, and it is difficult to control in the trade-off process. SUMMARY
[0005] The application provides a method for determining aircraft line replaceable unit based on maintainability and economy. The application solves the problem of unreasonable LRU division level in the existing aircraft type design process and frequent and repeated changes in the subsequent stage.
[0006] Technical scheme. A method for determining aircraft line replaceable unit based on maintainability and economy, comprising: S1. decomposing the aircraft according to function division to obtain a preliminary LRU pending item list; S2. Qualitative evaluation is performed according to qualitative influence factors determined in terms of reliability, maintainability, testability and supportability, considering the influence of relevant factors in the aircraft design stage and operation stage; S3. Qualitative evaluation is performed on the LRU pending items according to the evaluation points of the influence factors; for the items passing the qualitative evaluation, quantitative evaluation is performed on the candidate items of the LRU; S4. Calculation of the mean time to repair (MTTR) of the candidate items of the LRU is performed; S5. Calculation of the direct maintenance cost (DMC) of the candidate items of the LRU is performed; S6. After quantitative analysis of the candidate items of the LRU with MTTR and DMC as constraint conditions, comprehensive weighing method is adopted for evaluation, and the results of qualitative analysis and quantitative analysis are considered comprehensively to weigh the division of the LRU; S7. The aircraft LRU list is formed after comprehensive weighing and determination.
[0007] In the foregoing aircraft line replaceable unit determination method based on maintainability and economy, S1 is specifically as follows: the aircraft is subdivided to the bottom layer structure according to the functional division, and the preliminary LRU pending item list is obtained by splitting or combining the components in the system. In the foregoing aircraft line replaceable unit determination method based on maintainability and economy, in S3, for the items with difference or three or more good evaluations in the qualitative evaluation results, further analysis is performed in combination with FMEA and MMEL to check the influence of the items on the attendance, and it is determined whether the items need to be decomposed or redesigned.
[0008] In the foregoing aircraft line replaceable unit determination method based on maintainability and economy, in S4, the quantitative analysis calculation formula of the MTTR is as follows:
[0009] Among them, is the mean time to repair, is the failure rate of each component in the LRU, is the time required for each component of the LRU to complete one repair maintenance.
[0010] In the foregoing aircraft line replaceable unit determination method based on maintainability and economy, S5 is specifically as follows: the candidate items of the LRU are divided into planned disassembly repairable items, unplanned disassembly repairable items, planned disassembly non-repairable items and unplanned disassembly non-repairable items from the maintenance task point of view, and the calculation method of the items corresponding to the maintenance type is determined.
[0011] In the foregoing aircraft line replaceable unit determination method based on maintainability and economy, the calculation method of the DMC of the planned disassembly repairable item is as follows: .
[0012] The DMC calculation method of the repairable parts without planned disassembly in the foregoing aircraft route replaceable unit determination method based on maintainability and economy is as follows: .
[0013] The DMC calculation method of the non-repairable parts with planned disassembly in the foregoing aircraft route replaceable unit determination method based on maintainability and economy is as follows: .
[0014] The DMC calculation method of the non-repairable parts without planned disassembly in the foregoing aircraft route replaceable unit determination method based on maintainability and economy is as follows: .
[0015] Advantages of the present application: the present application proposes a complete LRU determination method, taking reliability, maintainability, testability, and supportability as evaluation influencing factors, qualitatively evaluating by referring to design and actual operation experience, quantitatively analyzing by taking mean time to repair (MTTR) and direct maintenance cost (DMC) as constraint conditions, and finally determining the LRU of the aircraft by comprehensive trade-off, so as to ensure that the LRU project level is reasonable, the quantity is optimal, and the process change is reduced.
[0016] The application provides a method for determining an aircraft route replaceable unit based on maintainability and economic constraints. In aircraft design, the division of LRUs directly affects maintenance efficiency, operating cost and dispatch reliability. The application solves the problems of traditional LRU division, such as strong subjectivity, lack of quantitative basis and repeated design in later stage, adopts a two-stage screening and comprehensive weighing process framework, based on reliability, maintainability, testability and supportability level, combines system-level failure mode and effects analysis (FMEA) and aircraft master minimum equipment list (MMEL), quickly screens LRU candidates from a large number of components, reduces the quantitative analysis range, and then accurately weighs through the establishment of maintainability and economic quantitative index constraints. Finally, through the comprehensive weighing of quantitative indexes, the optimal LRU division scheme is ensured. At the same time, aiming at the core pain point that there is a lack of data in the early stage of aircraft development and it is impossible to obtain sufficient data sources to determine the parameters, the application provides reliable reference values for initial calculation based on existing type experience, ensures that the quantitative analysis can be smoothly started in the early stage of type development, and makes the method of the application more engineering-oriented. Through the process, quantification and practicalization means, the method can combine qualitative screening and quantitative analysis in the early stage of aircraft type development from multiple dimensions and in a more detailed way, clearly divide and determine the LRU, provide a clear and reliable LRU division scheme at the design source, realize scientific decision-making in the early stage of type, optimize the maintainability and economy of the aircraft from the global perspective, solve the problem of unreasonable LRU division level and frequent and repeated changes in the subsequent design process of the existing aircraft type, and is an important support for realizing the positive design of the aircraft.
[0017] In summary, the LRU determination method provided by the application can realize reasonable division of LRU, improve the convenience of field maintenance, greatly save maintenance time and improve aircraft dispatch reliability. BRIEF DESCRIPTION OF DRAWINGS
[0018] Fig. 1 is an LRU determination process diagram provided by the application; Fig. 2 is an LRU qualitative judgment flowchart provided by the application; Fig. 3 is an LRU division comprehensive weighing flowchart provided by the application. DETAILED DESCRIPTION
[0019] To make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.
[0020] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.
[0021] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.
[0022] Example 1. A method for determining replaceable aircraft flight paths based on maintainability and economy, see [link to example]. Figs. 1-3 ,include: Step 1: Decompose the aircraft down to the lowest level of structure based on its functions, i.e., individual units and modules, until it cannot be further subdivided. Then, by reasonably splitting or merging certain components in the system, a preliminary list of LRU pending items is obtained.
[0023] Step 2: Taking into account the impact of various relevant factors in the aircraft design and operation phases, a set of evaluation criteria is applied to conduct a qualitative evaluation based on the qualitative influencing factors determined in four aspects: reliability, maintainability, testability, and supportability.
[0024] Step 3: Conduct a qualitative assessment of the LRU (Low Run Unit) candidates according to the evaluation criteria for influencing factors. For items with poor or more than three good ratings, further analysis is required using System-Level Failure Mode and Effects Analysis (FMEA) and the Aircraft Master Minimum Equipment List (MMEL) to examine their impact on availability and determine whether the item needs to be decomposed or redesigned. Items that pass the qualitative assessment can be considered as LRU candidates for quantitative assessment.
[0025] Step 4: Calculate the Mean Time To Repair (MTTR) for the LRU candidates. The quantitative analysis formula for MTTR is as follows:
[0026] in: It is the average repair time. It represents the failure rate of each component in the LRU. This is the time required for each component of the LRU to complete a corrective repair.
[0027] Step 5: Calculate the direct maintenance cost (DMC) for LRU candidates. From the perspective of maintenance tasks, LRU candidates are divided into repairable parts with planned disassembly, repairable parts without planned disassembly, non-repairable parts with planned disassembly, and non-repairable parts without planned disassembly. Determine the calculation method for items of different maintenance types.
[0028] Step Six: After quantitatively analyzing the LRU candidates using Mean Time To Repair (MTTR) and Direct Maintenance Cost (DMC) as constraints, it is necessary to comprehensively consider the results of qualitative and quantitative analyses and weigh the LRU classification.
[0029] Step 7: After comprehensive consideration and judgment, an aircraft LRU list is formed.
[0030] Example 2. (As shown) Figs. 1-3 As shown, the present invention provides a method for determining replaceable aircraft flight paths based on maintainability and economy, comprising: Step 1: Decompose the aircraft down to its lowest structural level, i.e., individual units and modules, based on functional divisions, until no further subdivision is possible. Then, by reasonably disassembling or merging certain components within the system, a preliminary list of LRU (Least Recently Used) items is obtained. For more complex equipment or equipment difficult to disassemble, it is generally defined as an LRU item, and further decomposition is not recommended. In the early stages of aircraft development or when various performance indicators are not yet determined, the following aspects should be considered when determining LRU items: (1) Refer to industry benchmarks (mature or similar models); (2) The repair time of the LRU should be lower than the field transit time (or mission preparation time). (3) There should be no restrictions on LRU field replacement in terms of regulations, safety, personnel special skills, special equipment, etc.; (4) Modularly designed electronic, electrical and mechanical components should allow their sub-components to be independently replaced on the aircraft (in situ); (5) When a component contains multiple parts, if a part has an independent function, then the part should be allowed to be independently replaced on the aircraft (in situ); (6) Components that have physical connections but no independent functions, and whose replacement or repair costs are low and whose reliability is high, can be considered to be merged into one LRU; (7) If the replacement or repair cost of a component is too high, it should be considered to split it into multiple LRUs.
[0031] Collect and compile specific information on these pending items, including product information, product failure rate, etc. See Table 1 for details.
[0032] Table 1 LRU pending item list (example)
[0033] Table filling instructions: (1) Column: product level: divided into two levels of level 1 and level 2, level 1 is the airborne equipment level, level 2 is the department accessory and module level, level 1 can be filled in according to the system product list, level 2 needs to be filled in according to the documents of each equipment manufacturer.
[0034] (2) Column: product status: divided into new research, modification, shelf.
[0035] (3) Column: part number: according to the installation level diagram number in the configuration requirement.
[0036] (4) Column: MTBF estimated value: filled in according to the reliability prediction report of each system, and the documents of each equipment manufacturer are referred to for level 2 products.
[0037] (5) Column: diagnosis method: filled in according to the requirements in the testability detailed design report of each system.
[0038] Step two: considering the influence of each related factor in the aircraft design stage and operation stage, a set of evaluation criteria is executed for qualitative evaluation according to the qualitative influence factors determined in reliability, maintainability, testability and supportability. The specific evaluation criteria are shown in table 2.
[0039] Table 2 qualitative influence factor evaluation table
[0040] Step three: according to the evaluation points of the influence factors in table 2, the LRU pending items are qualitatively evaluated. For the evaluation results with difference or three or more good evaluations, further analysis is needed in combination with system level failure mode and effect analysis (FMEA) and aircraft master minimum equipment list (MMEL) to check the influence of these items on attendance, and to determine whether the items need to be decomposed or redesigned. For the items that pass the qualitative evaluation, they can be used as the candidate items of LRU for quantitative evaluation. The LRU qualitative evaluation process is shown in Fig. 2 .
[0041] Step four: the mean time to repair (MTTR) of the LRU candidate items is calculated, and the quantitative analysis formula of MTTR is:
[0042] Wherein: is the mean time to repair, is the failure rate of each component in the LRU, is the time required for each component of the LRU to complete one repair maintenance.
[0043] Fill in the maintenance activity data of LRU candidates in Table 3.
[0044] Table 3 LRU candidate maintenance activity data table (example)
[0045] Table filling instructions: (1) Column: installation position: pay attention to the same items with large differences in different positions, and distinguish them when counting maintenance activity data to ensure the accuracy of the results.
[0046] (2) Column: preparation time: the time required for preparation before disassembling and replacing the failed LRU candidate, such as preparing maintenance tools, starting necessary ground equipment (maintenance personnel climbing to the surface of the aircraft, raising the lifting platform to the required position), draining system oil, etc. This time does not include opening the aircraft maintenance access, hatch, etc. (3) Column: access time: from opening the maintenance access, hatch, to the maintenance personnel reaching the position of the LRU candidate to be disassembled and replaced, preparing to start disassembly, which should include the time required to open the hatch, the time for personnel to move forward in the access, and the time to remove the shielding. (4) Column: disassembly and installation: the time required for disassembling the failed LRU candidate and installing the spare LRU candidate, which mainly includes the time required for disassembling and installing LRU candidate fasteners, electrical connectors, conduits, wires, etc. (5) Column: recovery time: after replacing the LRU candidate, the time required to restore the system and aircraft to normal state, mainly including sealing, supplementing oil, installing the shielding removed before, maintenance hatch, etc. (6) Column: debugging and testing: the time required for necessary debugging and testing of the LRU candidate and system after recovery.
[0047] (7) Column: cumulative time: the maintainability prediction of LRU candidates uses time accumulation method to estimate the time required for the following five maintenance activities for each LRU candidate: preparation time, access time, disassembly and installation, recovery time, and debugging and testing.
[0048] Calculate the maintainability prediction of LRU candidates by filling in Table 4.
[0049] Table 4 LRU candidate maintainability prediction table (example)
[0050] Table filling instructions: (1) Column: M ct : from the cumulative time in Table 3, unit: hour.
[0051] Column (2): Failure rate λ i : From the reliability prediction data provided by the equipment supplier.
[0052] Step five, calculate the direct maintenance cost (DMC) of LRU candidates, divide LRU candidates into planned disassembly repairable parts, unplanned disassembly repairable parts, planned disassembly non-repairable parts, and unplanned disassembly non-repairable parts from the perspective of maintenance tasks, and determine the calculation method of different maintenance types as follows: a) Planned disassembly repairable parts:
[0053] b) Unplanned disassembly repairable parts:
[0054] c) Planned disassembly non-repairable parts:
[0055] d) Unplanned disassembly non-repairable parts:
[0056] For specific parameter explanations and selections in the above formulas, Table 5 is explained, and for parameters determined by possible insufficient data sources, reference suggested values are given.
[0057] Table 5 DMC parameter selection table
[0058] Table 5 (continued)
[0059] Step six, after quantitative analysis of LRU candidates by average repair time (MTTR) and direct maintenance cost (DMC) as constraint conditions, the results of qualitative analysis and quantitative analysis need to be considered comprehensively, and the division of LRU is weighed, for quantitative indicators, MTTR should not exceed the index allocated to the system level in the maintainability design requirements, the DMC value of repairable parts should not exceed one thousandth of the project estimated price, and the DMC value of non-repairable parts should not exceed 0.5, the specific weighing method is as follows: 1. If the MTTR value and the DMC value do not exceed the limit value, it can be determined as LRU; 2. If one of the MTTR value and the DMC value exceeds the limit value, it can be determined as LRU, but it is recommended to optimize or re-decompose the project with two good qualitative analysis results; 3. If both MTTR and DMC values exceed the limit, the LRU cannot be determined unless the design is optimized and then re-evaluated until the requirements are met.
[0060] The LRU division comprehensive trade-off procedure based on the quantitative evaluation results is shown in Fig. 3 .
[0061] Step 7. After the comprehensive trade-off determination, a round of LRU list is formed, and the specific table form is shown in Table 6.
[0062] Table 6. LRU list (example)
[0063] The above description only expresses the embodiments of the present application, which is more specific and detailed, but cannot be understood as the limitation of the patent scope of the present application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which belong to the protection scope of the present application.
Claims
1. A method for determining replaceable aircraft flight paths based on maintainability and economy, characterized in that, include: S1. Decompose the aircraft according to its functions to obtain a preliminary list of LRU undetermined items; S2. Taking into account the impact of various relevant factors in the aircraft design and operation phases, a qualitative evaluation is conducted based on the qualitative influencing factors determined in four aspects: reliability, maintainability, testability, and supportability. S3. Conduct a qualitative assessment of the LRU candidates according to the key points of the influencing factor evaluation; for the candidates that pass the qualitative assessment, conduct a quantitative assessment as LRU candidates; S4. Calculate the mean repair time (MTTR) for the LRU candidates; S5. Calculate the direct maintenance cost (DMC) for LRU candidates; S6. Using MTTR and DMC as constraints, after quantitative analysis of LRU candidates, a comprehensive trade-off method is adopted for evaluation, and the results of qualitative and quantitative analysis are taken into account to weigh the LRU division. S7. After comprehensive consideration and judgment, an aircraft LRU list is formed.
2. The method for determining replaceable aircraft flight paths based on maintainability and economy as described in claim 1, characterized in that, S1 is as follows: Based on the functional division, the aircraft is subdivided to the lowest level of structure, and then the components in the system are split or merged to obtain a preliminary list of LRU pending items.
3. The method for determining replaceable aircraft flight paths based on maintainability and economy as described in claim 1, characterized in that, In S3, for items with poor or more than three good ratings in the qualitative assessment results, further analysis is conducted using FMEA and MMEL to examine the impact of these items on attendance and determine whether the item needs to be decomposed or redesigned.
4. The method for determining replaceable aircraft flight paths based on maintainability and economy as described in claim 1, characterized in that, In S4, the quantitative analysis formula for MTTR is as follows: in: It is the average repair time. It represents the failure rate of each component in the LRU. This is the time required for each component of the LRU to complete a corrective repair.
5. The method for determining replaceable aircraft flight paths based on maintainability and economy as described in claim 1, characterized in that, S5 is as follows: From the perspective of maintenance tasks, the LRU candidates are divided into repairable parts that can be disassembled according to plans, repairable parts that can be disassembled without plans, non-repairable parts that can be disassembled according to plans, and non-repairable parts that can be disassembled without plans, and then the calculation method for the corresponding maintenance type items is determined.
6. The method for determining replaceable aircraft flight paths based on maintainability and economy as described in claim 5, characterized in that, The calculation method for the DMC of repairable parts with planned disassembly is as follows: 。 7. The method for determining replaceable aircraft flight paths based on maintainability and economy as described in claim 5, characterized in that, The method for calculating the DMC of repairable parts that are not planned to be disassembled is as follows: 。 8. The method for determining replaceable aircraft flight paths based on maintainability and economy as described in claim 5, characterized in that, The calculation method for DMC of non-repairable parts that are planned to be disassembled is as follows: 。 9. The method for determining replaceable aircraft flight paths based on maintainability and economy as described in claim 5, characterized in that, The calculation method for DMC of unrepairable parts that are not planned to be disassembled is as follows: 。