For eighty years a pilot’s controls were connected to the wings by steel cables, pulleys and pushrods running the length of the aircraft. The A320 replaced almost all of it with wires carrying signals to computers, and computers commanding hydraulic actuators at each surface — lighter, more precise, and able to move each surface for reasons of its own, like smoothing gusts the pilot never felt.

The computers know the aircraft’s limits — stall angle, maximum speed, structural g — and simply will not cross them. A pilot escaping windshear can snap the stick fully back and hold it there: the aircraft gives its maximum climb performance, right at the edge of the stall, without stalling. Before fly-by-wire, that manoeuvre relied on nerve and feel; now it is guaranteed by design.

No single computer is trusted. The A320 carries seven flight-control computers of two different designs, written by separate teams, cross-checking each other. If one disagrees it is outvoted; if several fail, the aircraft steps down through simpler control laws and can still be flown. Redundancy through disagreement is now the template for every safety-critical system, in aircraft and beyond.

Because the "feel" of the aircraft is computed rather than mechanical, Airbus gave the A320’s cockpit and handling to every aircraft it designed afterwards — a pilot moves between the A320 and the giant A380 with days of training instead of months. That common type rating changed airline economics, and helped make the A320 family the best-selling airliner in history.