<div class="htmlview paragraph">This paper presents an updated overview of the Computer Aided System Engineering and Analysis (CASE/A)-ECLSS series modeling package. CASE/A is an Environmental Control and Life Support System (ECLSS) and Active Thermal Control System (ATCS) analysis and trade study tool developed primarily for VAX mainframe usage. The program was developed under NASA MSFC contract NAS8-36407 and is currently being used by MSFC and selected support contractors to support their Space Station Freedom WP-01 ECLSS preliminary design modeling activities. Many new additions and enhancements to the program have been incorporated since the first paper was presented on the topic three years ago. An extensive components verification program was completed to assure component modeling validity based on actual test data from the Phase II comparative test program recently completed at MSFC. An integrated plotting feature has been added to the system which allows the user to analyze on-screen data trends or obtain hard copy plots from within the CASE/A operating environment. Many new command features in the areas of model management, schematic management, component data editing, and output management have been incorporated to increase the engineer's productivity during a modeling session. CASE/A is a versatile modeling package that will prove beneficial during all phases of a spacecraft design program, from the initial conceptual design trade studies through the actual flight, including pre-flight prediction and in-flight anomaly analysis.</div>