This article discusses the cultural aspects of High Reliability Organizations (HROs), such as air navigation services. HROs must maintain a highly professional safety culture and constantly be prepared to handle crises. The article begins with a general discussion of the concept of organizational culture. The special characteristics of HROs and their safety culture is then described. Finally the article illustrates how Critical Incident Stress Management (CISM) is becoming an ingrained feature of the organizational culture in air traffic control systems. Critical Incident Stress Management is a prevention program that can successfully guard against the negative effects of critical incidents. The CISM program of DFS (Deutsche Flugsicherung) was recently evaluated by the University of Copenhagen. This evaluation not only confirmed the successful prevention of negative effects at the operation's employee level (especially air traffic controllers), but also showed a sustained improvement of its safety culture and its overall organizational performance. The special aspects of cross-cultural crisis intervention and the challenges it faces, as well as the importance of prevention programs, such as CISM, are illustrated using the examples of two aircraft accidents: the crash landing of a calibration aircraft and the Lake Constance air disaster.