Undependable systems are unable to accomplish the mission for which they were designed and cause tremendous loss [Airwar-Vietnam, 1978]. In most instances, timely maintenance is a vital necessity for a system to be kept in or returned to its operating condition, and to be able to successfully complete a specific mission. In a scarcer-resource but higher-competition environment, it is essential that system dependability be considered as a major system parameter and be evaluated during the early phases of the system design process.

Given a specific system mission profile, whether or not the mission can be successfully completed is based not only on such measures as performance, reliability, maintainability, and/or availability. There is a need for system designers and engineers to meeasure system dependability, as well. System dependability is a measure of effectiveness which allows for the consideration of maintenance in the life cycle as long as it does not inhibit the system from fulfilling its mission. It is the aim of this project to develop a methodology for the analysis and evaluation of system effectiveness through the utilization of the system dependability measure.

The concept and the mathematical model of system dependability is discussed. Effectiveness factors and relationships are described, a measure of system dependability has been defined, and a computer -based tool was developed to enable the accomplishment of trade-off analyses and the evaluation of various system configurations in terms of dependability. Maintenance requirements are addressed through the introduction of various combinations of failures, and failure distributions include the consideration of the exponential, Weibull, and log-normal cases.

Application of the dependability model is illustrated through a case study involving an aircraft radar trated through a case study involving an aircraft radar is illustrated through a case study involving an aircraft radar subsystem as an example.