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Reliability Growth

ALCL 131

DAU GLOSSARY DEFINITION

Alternate Definition

Reliability growth is the positive improvement in a reliability parameter over a period of time due to implementation of corrective actions to system design, operation or maintenance procedures, or the associated manufacturing process.

Alternate Definition Source

Military Handbook (MIL-HDBK)-189C, Reliability Growth Management

General Information

Background

In 1962, J. T. Duane of the General Electric (GE) Company published a report in which he presented failure data of different systems during their development programs. While analyzing the data, he observed that the cumulative Mean Time Between Failure (MTBF) versus cumulative operating time followed a straight line when plotted on logarithmic paper. Since that time, reliability growth planning has developed into a process that uses complex statistical techniques to develop growth curves as part of both design, test and program management activities.

What's Included?

Reliability growth management is part of the System Engineering (SE), Product Support Analysis (PSA), Developmental Test & Evaluation (DT&E), and Operational Test & Evaluation (OT&E) processes to include:

How is it Achieved?

As described in MIL-HDBK-189, reliability growth is achieved when a change to the design is effective in eliminating or mitigating a failure mode. A failure mode is the failure mechanism associated with a potential or observed failure. The FMECA plays a critical role in identifying failure modes and defining their impact at the local level (e.g. part level), thru the next higher level (e.g., circuit card) and at the system level, (e.g., the equipment level) in terms of their impact on operations. Failures due to an individual failure mode may exhibit a given failure rate until a corrective action (termed a fix) is made in the design, operation, maintenance, or manufacturing process that mitigates the failure mechanism.

Reliability growth programs and their associated testing implement a methodology known as the Test-Analyze-Fix-Test (TAFT) program. When a failure is observed under a TAFT program, testing stops until the failure is analyzed and a corrective action is incorporated on the system. Testing then resumes with a system that (presumably) has a better reliability. The graph of the reliability for this testing strategy is a series of small increasing steps that can be approximated by a smooth idealized curve. Reliability growth is measured as a function of the slope of the curve representing the cumulative numbers of failures versus the cumulative test duration for an individual system plotted on a logarithmic scale.

Reliability growth metrics reflects the rate at which the system’s reliability is improving as a result of implementation of corrective actions. A growth rate between zero and one (0,1) implies improvement in reliability, a growth rate of zero (0) implies no growth, and a growth rate less than zero (0) implies reliability decay.

Defense Science Board (DSB) Task Force

The DSB Task Force on DT&E was convened in 2007 to investigate the causal factors for the high percentage of programs entering Initial OT&E (IOT&E) in recent years which have been evaluated in the Director, OT&E (DOT&E) 2007 Annual Report as both not operationally effective and not operationally suitable. The DSB examined the root causes of poor suitability that resulted in a significant increase in the number of systems not meeting suitability requirements during IOT&E.

The Board found that several factors, to include 1990-era OSD changes to acquisition practices and reductions in acquisition personnel resulted in the weakening of engineering processes and the loss of skills in the areas of RAM. With some exceptions, the practice of reliability growth methodologies had been discontinued during the Technology Maturation and Risk Reduction (TMRR)) phase. Relevant military specifications, standards and other guidance were cancelled or not used, in favor of industry standards, which was a complicated transition.