Design considerations in Boeing 777 fly-by-wire computers

The new technologies in flight control avionics systems selected for the Boeing 777 airplane program consist of the following: fly-by-wire (FBW), the ARINC 629 data bus, and 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: the computing system, airplane electrical power, hydraulic power and communication paths. The multiple redundant hardware is required to meet the numerical safety requirements. Hardware redundancy can be relied upon only if hardware faults can be contained; fail-passive electronics are necessary building blocks for the FBW systems. In addition, the FBW computer architecture must consider other fault tolerance issues: generic errors, common mode faults, near-coincidence faults and dissimilarity.