A pre-prototype expert system called SLMES (Shuttle Leak Management Expert System) has been developed that enables an ECLSS (Environmental Control and Life Support System) subsystem manager to analyze subsystem anomalies and formulate flight procedures based on flight data. SLMES combines rule-based expert system technology with traditional FORTRAN-based software into an integrated system. SLMES uses rules to ask the user for configuration information and to prompt for flight data. SLMES analyzes the data using rules and when it detects a problem that requires a simulation it sets up the input for the FORTRAN-based simulation program ARPCS2AT2. This program predicts the cabin total pressure and composition as a function of time. The program simulates the pressure control system, crew O2 masks, airlock repress/depress valves, and leakage, etc. When the simulation has completed, other SLMES rules are triggered to examine the results for simulation contrary to flight data. For example, the simulation may calculate that more nitrogen is needed than what is available. If SLMES detects such a condition it will suggest methods to try to correct the problem and allow the user to re-run the simulation. Results are presented to the user in graphical and tabular form.This paper describes the expert system and how it can be used. The paper also describes how expert system technology can be applied to other areas.