A Fault Tolerance Assessment of DAIS

A functional/graphical approach is used to assess the fault tolerance of the Digital Avionics Information System (DAIS), a real-time federated multicomputer digital avionics system. Two separate assessments are made; first the functional/graphical approach is used to assess the fault tolerance of the DAIS architecture, then the utility of the functional/graphical approach itself is considered. The functional/graphical approach used has two complementary aspects; a functional characterization of fault phenomena, and a graphical approach to the representation of system behavior, both for normal operations and in response to faults. The graphical representation used is based on the LOGOS system description schema, which uses two associated graphs, a control graph and a data graph, to represent a process or activity. The study extends earlier functional/graphical studies of individual, isolated fault tolerance mechanisms, to the assessment of a complex large scale digital system. The assessment begins by modeling top level DAIS control functions and includes DAIS master executive functions and top level functions from a potential DAIS application.