NPFC - MIL-HDBK-189
RELIABILITY GROWTH MANAGEMENT
|Publication Date:||13 February 1981|
This handbook provides procuring activities and development contractors with an understanding of the concepts and principles of reliability growth, advantages of managing reliability growth, and guidelines and procedures to be used in managing reliability growth. It should be noted that this handbook is not intended to serve as a reliability growth plan to be applied to a program without any tailoring. This handbook, when used in conjunction with knowledge of the system and its development program, will allow the development of a reliability growth management plan that will aid in developing a final system that meets its requirements and lowers the life cycle cost of the fielded systems.
This handbook is intended for use on systems/equipments during their development phase by both contractor and government personnel.
The majority of reliability growth data analyses are statistical analyses. Statistical analyses view growth as being the result of a smooth, continuous process. In fact, reliability growth occurs in a series of finite steps corresponding to discrete design changes. Mathematical models describe the smooth expectation of this discrete process. Rather than being concerned about whether specific design changes are effected rapidly or slowly -- or whether they are very effective, not effective, or even detrimental--the statistical models work with the overall trend. In most situations, this is a desirable feature as it focuses attention on long-term progress rather than on day-to-day problems and fixes. The application of statistical analyses relies on analogy. For example, the growth pattern observed for program A may be used as a planned growth model for program B, because the programs are similar. As another example, the growth pattern observed early in program B may be extrapolated to project the growth expected later in the program because of similarities between the early and later portions of the program. The difficulty that occurs in applying the analogy approach is that perfectly analogous situations rarely exist in practice. The engineering analyses described in this section rely on synthesis. That is, they build up estimates based on a set of specific circumstances. There is still, however, reliance on analogy; but the analogies are applied to the parts of the problem rather than to the whole. Although synthesis may be used to provide a complete buildup of an estimate, it is simpler and more common to use synthesis to account for the differences, or lack of perfect analogy, between the baseline situation and the situation being analyzed.
The general approach to growth planning and long-term projection is similar to that used for assessment and short-term projection purposes. The main difference is that for planning and long-term projection purposes, attention must be directed to program characteristics and general hardware characteristics, since specific design changes are unknown at the time of program planning. For assessment and short-term projection purposes, attention must be directed to the specific hardware changes made or anticipated. For the most part, the program and general hardware characteristics can be ignored, since they have already played their role in determining the specific hardware changes. The only differences between assessment and short-term projection is whether a change has been incorporated in the hardware or not. The analysis is the same in both cases except that recent test results may be incorporated in the assessment. It should also be noted that the type of assessment described in this section, because of the judgment involved in arriving at it, is particularly suitable for use within an organization. For inter-organization use, completely objective demonstrated values, computed by a means acceptable to the organizations concerned, are usually necessary.