The Boeing Aircraft Company and Airbus Industries differ in their approaches in using fly-by-wire systems. In Airbus airliners, the flight-envelope control system always retains ultimate flight control, and it will not permit the pilots to fly outside these performance limits. However, in the event of multiple failures of redundant computers, the A320 does have mechanical back-up system for its pitch trim and its rudder. The A340-600 has a purely electrical (not electronic) back-up rudder control system, and beginning with the new A380 airliner, all flight-control systems have back-up systems that are purely electrical through the use of a so-called "three-axis Backup Control Module" (BCM)

With the Boeing 777 model airliners, the two pilots can completely override the computerized flight-control system to permit the aircraft to be flown beyond its usual flight-control envelope during emergencies. Airbus's strategy which was begun with Airbus A320 has been continued on subsequent Airbus airliners.