Appendix D. Tools

A number of tools are available to help you analyze and design complex systems. This appendix describes some of these tools and covers the following topics:

• Fault Tree Analysis

• Reliability Block Diagram Analysis

• Failure Modes and Effects Analysis

• Event Tree Analysis

Most of these tools are simple enough that they do not require specialized software; simple spreadsheets will do. Many other tools exist; however, they are beyond the scope of this book For more references and information, you can search the Internet for reliability engineering, high-assurance systems engineering, and the tools mentioned here.

You can classify the analysis and design tools described in this appendix as tools for doing top-down or bottom-up design. In most system designs, a combination of top-down and bottom-up design methods are used as appropriate for different portions of a design.

Top-down tools are:

• Fault tree analysis (FTA)

• Reliability block diagram (RBD)

Bottom-up tools are:

• Failure mode and effects analysis (FMEA)

• Event tree analysis (ETA). Sometimes, you can use ETA for top-down analysis.

You can use most of these tools hierarchically, that is, you can describe a system as a collection of components. You can then describe each component, in turn, as a collection of subcomponents. You can use the same tools and techniques to analyze both low-level components and high-level systems.