This is primarily accomplished by early concurrent

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Unformatted text preview: ectiveness and/or safety. (Such cases might include EVA and emergency repair procedures.) A maintenance time line analysis may be a simple spreadsheet or, at the other end, involve extensive computer simulation and testing. FMECAs and FMEAs. Failure Modes, Effects, and Criticality Analysis (FMECA) and Failure Modes and Effects Analysis (FMEA) are specialized techniques for hardware failure and safety risk identification and characterization. They are discussed in this handbook under risk management (see Section 4.6.2) and reliability engineering (see Section 6.2.4). For the maintainability engineer, the FMECA/FMEA needs to be augmented at the LRU/ORU level with failure prediction data (i.e., MTTF or MTBF), failure detection means, and identification of corrective maintenance actions (for the LSA task inventory). Maintainability Models . Maintainability models are used in assessing how well alternative designs meet maintainability requirements, and in quantifying the maintenance resource requirements. Modeling approaches may range from spreadsheets that aggregate component data, to complex Markov models and stochastic simulations. They often use reliability and time-to-restore data at the LRU/ORU level obtained from experience with similar components in existing systems. Some typical uses to which these models are put include: • • • • • • • Annual maintenance hours and/or maintenance downtime estimates System MTTR and availability estimates (see sidebar on availability measures on page 86) Trades between reliability and maintainability Optimum LRU/ORU repair level analysis (ORLA) Optimum (reliability-centered) preventive maintenance analysis Spares requirements analysis Mass/volume estimates for (space-based) spares Repair vs. discard analysis. LSA and LSAR. The Logistics Support Analysis (LSA) is the formal technical mechanism for integrating supportability considerations into the systems engineering process. Many of the above tools and techniques provide maintainability inputs to the LSA, or are used to develop LSA outputs. Results of the LSA are captured in Logistics Support NASA Systems Engineering Handbook Integrating Engineering Specialties In...
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