Mission-Critical and Safety-Critical Systems Handbook

Design and Development for Embedded Applications

Kim Fowler

• Publisher: Newnes
• Year: 2009
• ISBN:
  9780080942551
• Topic: Design
• Subtopic: Industrial Design

This handbook provides a consolidated, comprehensive information resource for engineers working with mission and safety critical systems. Principles, regulations, and processes common to all critical design projects are introduced in the opening chapters. Expert contributors then offer development models, process templates, and documentation guidelines from their own core critical applications fields: medical, aerospace, and military.

Readers will gain in-depth knowledge of how to avoid common pitfalls and meet even the strictest certification standards. Particular emphasis is placed on best practices, design tradeoffs, and testing procedures.

• Comprehensive coverage of all key concerns for designers of critical systems including standards compliance, verification and validation, and design tradeoffs
• Real-world case studies contained within these pages provide insight from experience

CHAPTER 1

Best Practices in Mission-Assured, Mission-Critical, and Safety-Critical Systems

Kim Fowler

1. Roadmap to This Book

The material in this book presents best practices in developing mission-assured, mission-critical, and safety-critical systems for medical devices, avionics, military equipment, and spacecraft subsystems. It is a disparate grouping. The good news is that there are threads of commonality in best practices among these systems. The acronyms may vary but best practices translate fairly easily from one area to another. The following are selected areas where best practices in one market often translate well into other markets:

• Defined processes, procedures, and quality assurance (QA) programs

• Collecting and managing requirements and setting priorities for their implementation

• Experimentation and prototyping

• Risk assessment—technological feasibility and business feasibility

• Rigorous software development processes

• Review and inspection

• Documentation

• Test planning, verification and validation, and acceptance testing

1.1. Systems Engineering

The material in this book takes a high-level architectural approach. In essence, it is systems engineering. Whether medical, avionics, military, or space, all deal with multiple disciplines, including (but not limited to) software, electronic hardware, mechanical subsystems, and operations. The systems engineering approach pulls these disciplines together into a framework that helps elucidate interactions between disciplines. Basic definitions that you will need for the remainder of the book follow:

System: A combination of elements or parts forming a complex or unitary whole; composed of components, attributes, and relationships. Typically these elements within a system form definable inputs, processing, and outputs. The interrelated components work together toward a common objective [1].

Systems engineering: An “engineering discipline whose responsibility is creating and executing an interdisciplinary process to ensure that the customer and stakeholder’s needs are satisfied in a high quality, trustworthy, cost efficient, and schedule compliant manner throughout a system’s entire life cycle. This process is usually comprised of the following seven tasks: State the problem, Investigate alternatives, Model the system, Integrate, Launch the system, Assess performance, and Re-evaluate. . . . [The] [s]ystems [e]ngineering [p]rocess is not sequential. The functions are performed in a parallel and iterative manner” [2]. Brian Mar states that systems engineers should adhere to the following basic core concepts:

• Understand the whole problem before you try to solve it

• Translate the problem into measurable requirements

• Examine all feasible alternatives before selecting a solution

• Make sure you consider the total system life cycle

• Test the total system before delivering it

• Document everything [2]

Everyone on the team should exercise the discipline of systems engineering. The leader of the effort, aside from the program manager, should be a systems engineer or a systems architect. The difference between engineering and architecting is that engineering is deductive work based on hard science, while architecting is inductive work that tends to be likened to art [3]. Both are important in systems engineering.

Mission assurance: “Mission [a]ssurance is a full life-cycle engineering process to identify and mitigate design, production, test, and field support deficiencies of mission success” [4].

“Mission [a]ssurance includes the disciplined application of system engineering, risk management, quality, and management principles to achieve success of a design, development, testing, deployment, and operations process. Mission [a]ssurance’s ideal is achieving 100% customer success every time. Mission [a]ssurance reaches across the enterprise, supply base, business partners, and customer base to enable customer success” [5].

“Mission-[a]ssured [d]esign is aimed at creating a robust, manufacturable system—one that does exactly what it is intended to do (its mission) despite the presence of variations, stresses, and uncertainties that can result in mission failure” [6].

Mission critical: “The term mission critical . . . refers to any factor (equipment, process, procedure, software, etc.) . . . [that] is crucial to the successful completion of an entire project. It may also refer to a project the success of which is vital to the mission of the organization which attempts it” [7].

Safety-critical systems: “A computer, electronic or electromechanical system whose failure may cause injury or death to human beings. . . . [Examples include] an aircraft or nuclear power station control system. Common tools used in the design of safety-critical systems are redundancy and formal methods” [8].

Quality: The degree for which the sum total of product characteristics fulfill all of the requirements of customers.

Process: A group of interrelated activities and resources that transforms inputs into outputs, often described by a block or flow diagram of events.

Procedure: Specific implementation of the process for a single, focused area of concern; typically step-by-step instructions.

Validation: The confirmation that the design, function, and operation of the final product satisfies the customer’s intent.

Verification: The objective tests of metrics that show that the final product meets the quantitative requirements.

1.2. Important Issues

Five basic issues affect every development:

• Integrity—Development requires an integrated approach.

• Interfaces—Most important actions occur at interfaces.

• Humanity—All problems have a human origin.

• Iteration—All levels of development should have feedback to revise direction and design.

• Multidimensions—There are no silver bullets for completing a project.

Integrity: An integrated approach requires integrity, which is defined as the “seamless whole.” This requires a “big-picture view” of how the parts fit into the whole. The project lead, in particular...

Table of contents

• Cover
• Title
• Copyright
• Contents
• About the Editor
• About the Contributors
• Chapter 1 Best Practices in Mission-Assured, Mission-Critical, and Safety-Critical Systems
• Chapter 2 Failsafe Software Design: Embedded Programming in a Fail-Certain World
• Chapter 3 Compliance Concerns for Medical Equipment
• Chapter 4 Software for Medical Systems
• Chapter 5 Best Practices in Spacecraft Development
• Chapter 6 Systems Engineering in Military Projects
• Index