This article gives a microworld approach to identify design requirements for better situation awareness. Two experiments were designed and conducted. In the first experiment, behaviors of operators who lost situation awareness were analyzed, and the following two findings were obtained: (a) Automation must provide an operator with feedback information on the control mode, even when it is the operator who changed a control mode, (b) Authority for control may have to be passed from an operator to automation for attaining safety in highly urgent situations. The second experiment was done to investigate how human-interface may affect an operator’s situation awareness. It is shown that human-interface must be carefully designed to externalize a mental model of the controlled process.