Early phase design phases of more and more complex systems enhance the need for a more interdependent decision-making process across design disciplines and processes. No clear system architecture design process in industry identifies support tools for system architects' need. In this paper, we conducted interviews and workshop with system architects in a major aerospace company in order to understand what system architecture design process is and what decision support tools are needed in this process. The analysis of the collected data has underlined 10 different decision domains that we define and link to the needs expressed by the systems architects interviewed.