Maintainability engineering


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Maintainability engineering

  1. 1. MAINTAINABILITY ENGINEERING Maintainability Analysis Purpose The purpose of this task is to translate data from contractor’s studies, engineering reports and information which is available from the Contracting Activity (CA) into a detailed design approach and to provide inputs to the detailed maintenance and support plan, which is part of the Logistics Support Analysis (LSA). The four main goals are: • To establish design criteria that will provide the desired system features • To allow for design decisions to be made through the evaluation of alternatives and through the use of trade-off studies • To contribute toward establishing maintenance, repair and servicing policies and support maintainability achievement • To verify that the design complies with maintainability design requirements Scope The following Table reproduced from MIL-STD-470B (Maintainability Program For Systems And Equipment) contains identification to show when the Maintainability Analysis (Task 205) is used in different Program Phases. In the Contract Data Requirements List (CDRL), the Task 205 is referred as DI-R-7109 and the recommended delivery date to the customer is 30 days prior to PDR & CDR TASK TITLE TASK TYPE PROGRAM PHASE OSD Concept 205 Maintainability Analysis ENG Validatio n FSD Production S(3) G(3) G(1) C(1) ENG - Maintainability Engineering OSD - Operational System Developments (Modifications) G - Generally Applicable S - Selectively Applicable C - Generally Applicable to design changes only (1) - Requires considerable interpretation of intent to be cost effective (3) - Appropriate for those task elements suitable to definition during phase Hilaire Ananda Perera PEng Long Term Quality Assurance S
  2. 2. MAINTAINABILITY ENGINEERING Maintainability Analysis, Continued Definitions CDRL = Contract Data Requirements List PDR = Preliminary Design Review CDR = Critical Design Review FSD = Full Scale Development MTTR = Mean Time To Repair Mmax(φ) = Maximum Time To Repair for the φ percentile BIT = Built - In - Test Responsibilitie s It is the responsibility of the maintainability engineer assigned to the particular project to do the Analysis. The Analysis should be reviewed and approved by the Maintainability Group Leader and the Project Manager. Procedure The maintainability analysis integrates data from contractor’s studies with engineering reports and information which is available from the CA into a detailed design approach. Outputs from Tasks 201 and 202 of MIL-STD2165, if called out should form the basis for testability and diagnostic analysis. The elements specified in the Statement Of Work and to be considered in the maintainability analysis should include: • Mean Time To Repair (MTTR) and Maximum Time To Repair for the φ percentile (Mmax(φ)) for all levels (organizational, intermediate, depot) of maintenance. MIL-HDBK-472 Notice 1, Procedure V is an easy method for this task. If repair times cannot be synthesized from data books, time and motion studies should be performed and data statistically corrected to obtain times for analysis. • Maintenance man-hours and maintenance time expended/maintenance task/flight hour/operating hour for all appropriate levels of maintenance • False Alarm Rates (FAR), Cannot Duplicate (CND) Rates, Retest OK (RTOK) Rates associated with all levels of maintenance Hilaire Ananda Perera PEng Long Term Quality Assurance
  3. 3. MAINTAINABILITY ENGINEERING Maintainability Analysis, Continued Procedure (Continued) • Proportion of faults detectable (all levels of maintenance, including system/equipment/unit built-in detection, and external fault detection subsystems) • Level(s) of isolation or ambiguity (for example, does the built-in-test or external test system or tester identify N possible units or assemblies etc., only one of which is failed) for the system, equipment, unit, assembly, subassembly, etc., for each level of maintenance. • Identification of the required mix of automatic, semiautomatic, built-in and manual test capability, plus the maintenance aids and manual diagnostic procedures required at all levels of repair and their associated software and technical costs, skill levels required and manpower requirements, as well as acquisition costs if available. • Levels of repair associated with each equipment design and each test system alternative as derived from the LSA. • Development of unique external test systems and testers versus use of existing units (stock listed or commercial) • Producibility considerations relating to the realization of each test system alternative. • Determination of system/subsystem/equipment parameters that are monitored and not monitored by BIT or other diagnostic/test systems. • Impact of scheduled and preventive maintenance workload: • Mean time between scheduled and preventive maintenance at each required level of maintenance • Mean preventive maintenance time Hilaire Ananda Perera PEng Long Term Quality Assurance
  4. 4. MAINTAINABILITY ENGINEERING Maintainability Analysis, Continued Procedure (Continued) • Maintainability mathematical models, life cycle cost models, and acquisition cost estimates if specified in the Statement Of Work should be developed from the inputs and considerations described above to: • Show the impacts on cost, maintainability and on system readiness parameters of the germane maintainability elements • Allocate quantitative maintainability requirements to all significant item levels of the system/subsystem/equipment. (details are in Task 202 of MIL-STD-470B) • Develop the most cost effective maintainability design and test system configuration which meets support and personnel constraints as well as system readiness and mission performance objectives • Performance Design Trade-offs. NOTE: This task has significant possibilities for overlap with LSA efforts, and should therefore be coordinated closely with the LSA community and LSA Statement Of Work, to ensure consistency and prevent duplication. • Trade-offs between maintainability design alternatives and equipment design parameters should be made to provide an economical design which best satisfies systems or equipment requirements • Trade-offs involving impacts on maintainability attributed to changes in areas such as packaging, fault detection and isolation portions of the design or to external test equipment or testers should be incorporated in status reports submitted . Hilaire Ananda Perera PEng Long Term Quality Assurance
  5. 5. MAINTAINABILITY ENGINEERING Maintainability Analysis, Continued Associated Documents Customer provided Statement Of Work and the Equipment Specifications ISO 9001 Level II Document: Design Control - The Product Assurance Process MIL-STD-470: Maintainability Program For Systems And Equipment MIL-HDBK-472: Maintainability Prediction MIL-STD-2165: Testability Program For Electronic Systems And Equipment MIL-STD-721: Definitions Of Terms For Reliability And Maintainability Hilaire Ananda Perera PEng Long Term Quality Assurance