Quality Assurance

The opening statement of the National Aeronautics and Space Administration's (NASA) quality assurance policy says, “It is NASA policy to comply with prescribed requirements for performance of work and to provide for independent assurance of compliance through implementation of a quality assurance program.” How NASA defines quality and accomplishes this objective is the subject of this chapter. Various definitions for product “quality” have been used by the US government and private industry in the past. Commonly thought of, and defined in qualitative terms, as a measure of “goodness,” modern definitions generally define quality in terms of product compliance, which allows for the objective measurement of whether quality is achieved. The most widespread and internationally accepted definition of quality, defined by the American National Standards Institute (ANSI), the International Organization for Standardization (ISO), and the American Society for Quality (ASQ), set forth in ANSI/ISO/ASQ Q9000, is: “Degree to which a set of inherent characteristics fulfills requirements.” The ANSI/ISO/ASQ definition for quality is indifferent to whether fulfillment of requirements would result in mission success or whether personnel would be safe as long as the requirements are met. By this definition, if the design requirements are flawed, the quality program would only serve to ensure that the flawed requirements are met. Consequently, NASA has expanded upon the definition to include the concepts of mission success and personnel safety. The term “quality,” as used within the context of NASA's quality assurance policy, means “the development and compliance with requirements which provide for personnel safety and mission success.” An organization's quality program can, thus, be thought of as having two distinct components: Development of requirements that serve to keep people safe and achieve mission objectives. Assuring compliance with these requirements. “Quality assurance” (QA) is the name given to the second of these two components. The two components of quality are both essential and are interdependent. When viewed from a safety/mission success perspective, quality assurance is irrelevant if the technical/safety requirements are “bad” and the requirements are irrelevant if they are not met. From the standpoint of SHM, quality assurance is one mechanism needed to achieve system dependability. Dependability, the attribute of the system that measures its ability to meet system goals and objectives, is defined with respect to a system's goals and objectives, as opposed to its requirements, because of the potential issues with requirements described above. In this chapter, we shall focus on NASA's quality assurance program as a means of ensuring the end state of quality – safety and mission success – for aerospace systems. QA processes focus on proper performance of future, in-process, and post work, to minimize human causation of product defects that would lead to failure or degradation of the system's components and hence its functions. It is less directly connected to the specifics of the system design that detect and respond to failures than it is with the processes to ensure that the design is properly implemented, manufactured, and operated. QA can be considered as a mechanism to implement “failure prevention” functions of SHM. As described in Chapter 1, failure prevention often appears as a set of active operational measures. From this perspective, QA consists of active operational measures to reduce human mistake rates (faults) in the many of the activities of design, manufacturing, and operations. Lowering of human mistake rates means that the system will have fewer faults than it otherwise would have had, and thus QA serves to prevent potential failures.