Fault-tolerance in the Advanced Automation System

The Advanced Automation System (AAS), a distributed real-time system intended to replace the present en-route and terminal approach US air traffic control computer systems over the next decade, is discussed. High availability of air traffic control services is an essential requirement of the system. The authors discuss the general approach to fault tolerance adopted in the AAS by reviewing some of the questions asked during the system design, various alternative solutions considered, and the reasons for the design choices made.