Approaches to assure safety in fly-by-wire systems: Airbus vs. boeing

Fly-by-wire (FBW) is a flight control system using computers and relatively light electrical wires to replace conventional direct mechanical linkage between a pilot’s cockpit controls and moving surfaces. FBW systems have been in use in guided missiles and subsequently in military aircraft. The delay in commercial aircraft implementation was due to the time required to develop appropriate failure survival technologies providing an adequate level of safety, reliability and availability. Software generation contributes significantly to the total engineering development cost of the high integrity digital FBW systems. Issues related to software and redundancy techniques are discussed. The leading commercial aircraft manufacturers, such as Airbus and Boeing, exploit FBW controls in their civil airliners. The paper presents their approach, the difference of control philosophy, and the implementation resulting in a comparable level of safety assurance essential for airline operations.