Reliability, Maintainability, and Supportability

Best Practices for Systems Engineers

Michael Tortorella

• Publisher: Wiley
• Year: 2015
• Print ISBN: 9781118858882
• eBook ISBN: 9781119058502
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Industrial Engineering
• Index: Technology & Engineering

Focuses on the core systems engineering tasks of writing, managing, and tracking requirements for reliability, maintainability, and supportability that are most likely to satisfy customers and lead to success for suppliers

This book helps systems engineers lead the development of systems and services whose reliability, maintainability, and supportability meet and exceed the expectations of their customers and promote success and profit for their suppliers. This book is organized into three major parts: reliability, maintainability, and supportability engineering. Within each part, there is material on requirements development, quantitative modelling, statistical analysis, and best practices in each of these areas. Heavy emphasis is placed on correct use of language. The author discusses the use of various sustainability engineering methods and techniques in crafting requirements that are focused on the customers' needs, unambiguous, easily understood by the requirements' stakeholders, and verifiable. Part of each major division of the book is devoted to statistical analyses needed to determine when requirements are being met by systems operating in customer environments. To further support systems engineers in writing, analyzing, and interpreting sustainability requirements, this book also

• Contains "Language Tips" to help systems engineers learn the different languages spoken by specialists and non-specialists in the sustainability disciplines
• Provides exercises in each chapter, allowing the reader to try out some of the ideas and procedures presented in the chapter
• Delivers end-of-chapter summaries of the current reliability, maintainability, and supportability engineering best practices for systems engineers

Reliability, Maintainability, and Supportability is a reference for systems engineers and graduate students hoping to learn how to effectively determine and develop appropriate requirements so that designers may fulfil the intent of the customer.

Part I
Reliability Engineering

1
Systems Engineering and the Sustainability Disciplines

1.1 PURPOSE OF THIS BOOK

1.1.1 Systems Engineers Create and Monitor Requirements

The textbook marketplace offers many high-quality books that provide the student, professional, and researcher with many points of view on the sustainability disciplines of reliability engineering, maintainability engineering, and supportability engineering. The point of view we advance here, though, is different from that of other books. This book focuses intently on the roles and responsibilities of the systems engineer in creating and monitoring the requirements for reliability, maintainability, and supportability that will guide development of products and services that are most likely to satisfy their customers and lead to success for their suppliers. Systems engineers play a pivotal role in this process. Get the requirements wrong and the likelihood of a successful product or service is almost nil. That, coupled with the importance of acting as early as possible in the development process to build in quality and reliability, compels a new emphasis on preparing systems engineers to understand how the sustainability disciplines contribute to product and service success and to enlarge their toolkit to incorporate generation and validation of sustainability requirements that promote greater product and service success. The first major purpose of this book is to provide systems engineers with the knowledge they need to craft clear, concise, and effective sustainability requirements so that they may fulfill their role of key leader in successful product and service development.

Customers and suppliers also want to know whether requirements are being met by deployed products and services. For example, many telecommunications service providers offer service-level agreements (SLAs) to their larger customers (see Section 8.6). SLAs are usually based on certain service reliability criteria [11, 12]; when these criteria are violated, the customer is offered a full or partial refund for a stated period of service. In addition, many suppliers of commercial and consumer products offer warranties. The cost of servicing the warranty is borne by the supplier. The obvious financial consequences in these examples show why it is important to be able to determine in a systematic way whether and to what degree relevant requirements are likely to be met (in a planning phase) and are being met (in operation). Accordingly, the second major purpose of this book is to provide systems engineers with the concepts, tools, and techniques needed to carry out analyses for determining conformance to quantitative sustainability requirements.

1.1.2 Good Requirements are a Key to Success

Accepting, as we do, that a design faithfully realizing a set of complete and effective requirements will make a product or service that is no more or less than those requirements describe, it is clear that requirements are key contributors to a successful product or service. Accordingly, we need to understand what makes a good requirement. At least two important properties of a good requirement can be immediately discerned:

1. The requirement is written to promote an outcome (product or service property or behavior) that is desired by the customer.
2. The requirement is unambiguous: clear criteria are available to determine whether the requirement is met or not.

Every product or service property or behavior that is needed or desired by the customer for the product or service should be the subject of some requirement(s). There is no other reliable way to ensure that the product or service will have that property or behavior. This is nothing more than a restatement of the idea that if you want something, unless you ask for it specifically, you will only get it by some happy accident. Think of a customer, like a telecommunications service provider, who needs a reliable backup generator to ensure continuity of service during periods when utility power is unavailable. If the customer does not specify the length of time for which the backup generator is required to operate without failure, then the system designer has no guidance about how to specify which backup generator to use and what measures need to be taken to ensure that it operates for the needed period of time. Some backup generator will be chosen, but the reliability of that backup generator may or may not be good enough to meet the customer’s need. In this example, “you get what you get” without a clear plan to get, rather, what you need—the result is haphazard rather than systematic. Good requirements are complete (cover all properties and behaviors needed and desired by the customer).

The best way to promote unambiguous requirements is to state them in quantitative terms. Most requirements in the sustainability disciplines involve some quantitative variable. For example, we may wish to limit the amount of time it takes to complete a specified repair. To enforce such a limit, this duration will be the subject of a requirement. In practice, the time it takes to complete a repair is influenced by many factors, including control factors (those that the system designer and operator are able to control) and noise factors (factors that are thought of as “random” and not able to be readily adjusted by the designer or operator).¹ Consequently, it is customary to conceptualize the quantitative variables appearing in requirements as random variables in the sense used in probability theory. That is, the values taken by this variable over the different members of the population of products or service realizations may differ from one to another in unpredictable ways. For instance, the duration of the specified repair in the example will be influenced by factors like the location and ease of access of required spare parts, the location and...

Table of contents

• Cover
• Title page
• Table of Contents
• Foreword
• Acknowledgments
• Part I: Reliability Engineering
• Part II: Maintainability Engineering
• Part III: Supportability Engineering
• Index
• Wiley Series in Systems Engineering and Management
• End User License Agreement