Why did fly-by-wire systems take so long to implement? The first commercial FBW airplane was the Airbus A320, which was introduced in the late 1980s. This system only worked after decades of research by American and European aerospace companies. If FBW only converts mechanical motions from an airplane's control yoke into electrical signals (along with sensor feedback), which change the aircraft's control surfaces, what caused FBW to be implemented so late, besides the abundance of computers even before the A320? Can someone also check my understanding of FBW?

My understanding of FBW:


Aircraft manufacturers use rotary encoders and potentiometers to translate mechanical changes in the control yoke into electrical signals.
The FBW computer(s) use feedback from the aircraft's sensors, and compare it with the pilot's input. A derivative based FLL system is used, perhaps?
Hydraulic valves/servo motors are used by the FBW system to change the state of control surfaces.


Thank you.
A simple answer is that the aircraft control system has ultimate responsibility for survival of the aircraft. If it completely fails, you are as good as dead in most cases. Short of in-flight destruction, hardly anything can be worse.

Thus, full-authority (i.e. without mechanical backup) FBW gained acceptance only when the confidence in its overall reliability was sufficiently high. Naturally, it appeared on military airplanes first, where demands to reliability can be lower (the pilot can eject, after all), while demands to the control system sophistication are often higher.

(Others have already commented that A320 wasn't the first commercial airliner with FBW; Concorde had it much earlier. As for your understanding of FBW, it's basically correct. Sometimes, strain gauges rather than potentiometers are used as control stick sensors: force as the primary input is generally better than displacement).