The distributed real-time system services developed by Lockheed Martin's Air Traffic Management group serve the infrastructure for a number of air traffic control systems. Either completed development or under development are the US Federal Aviation Administration's Display System Replacement (DSR) system, the UK Civil Aviation Authority's New Enroute Center (NERC) system, and the Republic of China's Air Traffic Control Automated System (ATCAS). These systems are intended to replace present en route systems over the next decade. High availability of air traffic control services is an essential requirement of these systems. This article discusses the general approach to fault-tolerance adopted in this infrastructure, by reviewing some of the questions which were asked during the system design, various alternative solutions considered, and the reasons for the design choices made. The aspects of this infrastructure chosen for the individual ATC systems mentioned above, along with the status of those systems, are presented in the Section 11 of the article.