This project is an exploratory step into the development of new methodologies to aid in the design for maintainability of computer-integrated manufacturing systems. It will study the underlying sources of maintenance downtime and fault diagnosis difficulty in computer-integrated production systems. The project has two components. The first involves collecting and analyzing plant-based field data on the amount of downtime associated with various kinds of failures, including information on frequency of failures and the amount of downtime per failue. The second component is an experimental study to understand what makes these failures difficult to diagnose. The experimental study will utilize professional troubleshooters to diagnose faults in a computer-based model of the process control of a manufacturing cell.