A fault tolerant fly by wire system for maintenance free applications

The authors describe a triplex primary flight computer system based on a reconfigurable architecture with extensive use of application specific integrated circuits (ASICs). The system comprises fault-tolerant fly-by-wire (FBW) computers which are triplex dissimilar in both software and hardware. These command actuator control electronics (ACE) units via DATAC (ARINC 629) data buses. The FBW computers form the core of the full-authority FBW system and perform all the computational commands for the pitch, roll, and yaw surface actuation systems. The authors review the architectural design issues in terms of integrity requirements and fault tolerance, leading to a design which not only meets civil safety requirements but also has ultra-high-reliability, offering little or no maintenance action. The FBW computer architecture is based on dividing the basic path into three subfunctional elements. Each of these elements is then replicated to provide fault tolerance. The internal element redundancy management function is performed both in hardware and software, and it is able to detect and isolate faulty elements and perform the necessary reconfiguration. The current expectation for system reliability gives an expected time to 95% probability of dispatch of 38100 operating hours and has a predicted MTBMA of 92700 operating hours per shipset.<>