AIRBUS A320/A330/A340 electrical flight controls - A family of fault-tolerant systems

The digital electrical flight control system of the Airbus A320/A330/A340 is discussed. The A320 was the first civil aircraft equipped with such a system. It was certified and entered into service in the first quarter of 1988. The A330 and A340 have identical systems, closely related to the A320 system. These systems are built to very stringent dependability requirements both in terms of safety (the systems must not output erroneous signals) and availability. The basic building blocks are fail-safe control and monitoring computers. The control channel performs the function allocated to the computer (control of a control surface for example). The monitoring channel ensures that the control channel operates correctly. A high level of redundancy is built into the system. Special attention has been paid to possible external aggressions. The system is built to tolerate both hardware and software design faults. The A320 system is described together with the significant differences between the A320 and the A330/A340, and A320 in service experience.