Dealing with dependability requirements is a complex task for stakeholders and analysts as many different aspects of a system must be taken into account at the same time: services characteristics and quality properties, failure modes and tolerable failure rates, reactions and recovery time in case of failure, and so on. Visualization helps cope with this complexity. In this paper, we build upon a practical framework for eliciting and modeling dependability requirements to show how graphical data representation can facilitate requirements analysis during the requirements elicitation and definition process. An Air Traffic Control System, adopted as a Testbed within the NASA High Dependability Computing Project, is used as a case study.