Reliability Growth Enhancing Defense System Reliability (2015) / Chapter Skim
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1 Introduction
1 Introduction
Pages 19-30
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From page 19... ...
PANEL CHARGE AND SCOPE OF STUDY DoD originally asked the Panel on Reliability Growth Methods for Defense Systems to provide an assessment only of the use of reliability growth models to address a portion of the problem. Reliability growth models are used to track the extent to which the reliability of a system in development is on a trajectory that is consistent with achieving the system requirement by the time of its anticipated promotion to full-rate production.
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And, as noted in the charge, this report builds on previous work by the NRC's Committee on National Statistics. The procedures and techniques that can be applied during system design and development include system design techniques that explicitly address reliability and testing focused on reliability improvement.
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After seven years in production, the Air Force had to budget an additional unplanned $400 million for the F-22A to address numerous quality problems and help the system achieve its baseline reli ability requirements. ACHIEVING RELIABILITY REQUIREMENTS: KEY HISTORY AND ISSUES The magnitude of the problem in achieving reliability requirements was described at the panel's workshop by Michael Gilmore, the Director of Operational Test and Evaluation (DOT&E)
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From page 22... ...
plotted estimated reliabilities in comparison with requirements for all operational tests of ACAT I Army systems between 1997 and 2006: only one-third of the systems met their reliability requirements. The Defense Science Board also found substantial declines in the percentage of Navy systems meeting their reliability requirements from 1999 to 2007.3 These plots strongly indicate that there was an increasing problem in DoD regarding the ability to achieve reliability requirements in recent defense acquisition programs, especially for the higher-priced systems (those in which the Office of the Secretary of Defense is obligated to become involved)
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From page 23... ...
The result of inadequate initial design work is often late-stage adjustments of system design, and such redesigning of a system to address reliability deficiencies after a design is relatively fixed is more expensive than addressing reliability during the initial stages of system design. Moreover, late-stage design changes can often result in the introduction of other problems in a system's development.
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From page 24... ...
In response, the department has produced or modified a number of its guidances, handbooks, directives, and related documents to try to change existing practices. These documents support the use of more up-front reliability engineering, more comprehensive developmental testing focused on reliability growth, and greater use of reliability growth modeling for planning and other purposes.6 Two important recent documents are DTM-11-003 (whose improvements have been incorporated into the most recent version of DoDI 5000.02)
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From page 25... ...
KEY TERMS IN DEFENSE ACQUISITION The assessment of defense systems is typically separated into two general operational assessments: the assessment of system effectiveness and the assessment of system suitability: • Operational effectiveness is the "overall degree of mission accom plishment of a system when used by representative personnel in the environment planned or expected for operational employment of the system considering organization, doctrine, tactics, survivability or operational security, vulnerability, and threat." (U.S. Depart ment of Defense, 2013a, p.
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From page 26... ...
. Maintainability is "the ability of an item to be retained in, or restored to, a specified condition when maintenance is performed by personnel having specified skill levels, using prescribed procedures and resources, at each prescribed level of maintenance and repair" (U.S.
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From page 27... ...
These steps greatly increase the chances that the final system will satisfy its reliability requirements. The reliability engineering techniques that are currently used in industry to produce a system design consistent with a reliable system prior to reliability testing are referred to collectively as "design for reliability" (see Chapters 2 and 5)
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From page 28... ...
In fact, as Paul Ellner11 described at the panel's workshop, for a substantial percentage of defense systems, reliability as assessed in operational testing is substantially lower than reliability of the same system as assessed in developmental testing. This difference is often not explicitly accounted for in assessing which systems are on track to meet their requirements: this lack of recognition of the difference may in turn account for the failure of many systems to meet their reliability requirements in operational testing after being judged as making good progress toward the reliability requirement in developmental testing and evaluation.
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From page 29... ...
In this report, we examine the applicability of industrial practices to DoD, we assess the appropriateness of recent reliability enhancement initiatives undertaken by DoD, and we recommend further modifications to current DoD acquisition processes. As noted, in addition to the use of existing design for reliability and reliability testing techniques, we were asked to review the current role of formal reliability growth models.
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From page 30... ...
Chapter 7 discusses the design and evaluation of reliability growth testing relevant to developmental testing. Chapter 8 details the design and evaluation of reliability growth testing relevant to operational testing.
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