Safety critical avionics for the 777 primary flight controls system

The new technologies in flight control avionics systems selected for the Boeing 777 airplane program consists of the following: Fly-By-Wire (FBW), ARINC 629 Bus, Deferred Maintenance. The FBW must meet extremely high levels of functional integrity and availability. The heart of the FBW concept is the use of triple redundancy for all hardware resources: computing system, airplane electrical power, hydraulic power and communication path. The architecture of the 777 flight controls system follows the earliest Boeing 7J7 design. The Boeing designed global DATAC bus, also known as ARINC 629 data bus, is used to communicate among all computing systems. Each DATAC bus is isolated, both physically and electrically from the other two. The three DATAC buses are not synchronized. The control system performance under the autonomous and asynchronous DATAC bus operation has been studied. The primary flight computers (PFCs) form a triple-triple redundant system; three PFC channels and three computing lanes in each channel. Each channel is also isolated, both physically and electrically from the other two. The microprocessor hardware for three computing lanes in each channel are dissimilar to facilitate detection of generic design errors of the most complicated hardware devices; microprocessors. The Byzantine general problem has been considered in the design of the PFC redundancy management to cope with functional asymmetry and communication asymmetry. The deferred maintenance is to provide hot spare modules within an LRU such that the airplane dispatchability can be enhanced. This concept is applied to the three major avionics systems, PFC, Air Data Inertial Reference System (ADIRU) and Airplane Information Management System (AIMS).