Mechanical and hydro-mechanical flight control systems (cables, pushrods, hydraulics) all offer pilots some form of feedback – direct or, in the case of hydraulics, artificial – as the aircraft maneuvers and forces are applied to the controls. I know that early FBW, like that in the F-16 prototypes, used a rigid system that often allowed pilots to over-control the aircraft.

Do fly-by-wire-equipped airliners, like their non-FBW siblings, use an artificial feel system to provide control feedback?

up vote 8 down vote accepted

After some digging, I found an answer for myself: yes, some FBW airliners use artificial feel systems, but not all of them. According to Electronics in the Evolution of Flight (Google Books),

The [Boeing] 777 fly-by-wire system employs envelope protection. This feature of the artificial-feel system provides increasingly greater force when the aircraft is pushed to its limits.

Conversely, Airbus does not provide any feedback to the pilots as their flight control system enforces control laws that cannot be overridden by inputs (source: Aerospatiale engineering document):

The positioning of the control surfaces is no longer a simple reflection of the pilot’s control inputs and conversely, the natural aerodynamic characteristics of the aircraft are not fed back directly to the pilot.


Getting regulatory, since I did some further research: 14 CFR 29.395, certification of Transport Category aircraft, only states that the controls are required to resist a certain amount of force (i.e., not break). This differs from how much force is required to "achieve the positive limit maneuvering load factor" or otherwise impart changes to the aircraft's orientation (14 CFR 23.155 / 23.157).

  • This should be: "Conversely, Airbus does not provide any feedback to the pilots as their flight control system normally enforces control laws that cannot be overridden by inputs..." – Lnafziger Jan 27 '14 at 0:26
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    I would actually argue that the simple spring loading of Airbus side-stick provides exactly the feel that it should except when you hit the flight envelope limit. – Jan Hudec May 28 '14 at 19:08
  • Envelope protection is different than an artificial feel to the controls. – Carlo Felicione Apr 29 '17 at 3:08
  • 14 CFR Part 29 covers Transport Category Rotorcraft. Part 25 covers Transport Category Airplanes. But even Part 25 does not specify forces other than an allowable maximum force for the different controls. §25.397 Control system loads. – Gerry Apr 29 '17 at 14:12
  • Sorry but the quoted source does not say that Airbus does not provide any feedback. The quote is in the context that by removing the mechanical connection there is no direct feedback from the surfaces to the controls. As Jan mentions the spring loading and profile of the stick will provide artificial feedback to the pilot. – Adrian Aug 24 '17 at 8:12

Yes FBW aircraft use an artificial feel system to provide control feedback. Artificial, as in: there is no feedback to the stick from the airflow forces on the control surfaces, and the stick would feel very light if not loaded by some sort of mechanical feel spring. The mechanical feel spring makes the feel artificial; the spring can have a constant stiffness, or a varying stiffness as function of airspeed (q-feel).

All FBW must have artificial force feel because there is no direct mechanical connection between the control surface and the stick. Also all irreversible flight controls must have artificial force feel: although there is a mechanical link between stick and surface, aerodynamic moments on the control surfaces are not fed back through the hydraulic actuators that move the surface. The extent of the feedback feel depends on the manufacturer:

  • Airbus was the first airliner manufacturer to introduce fly-by-wire, in the A320. They chose for uncoupled sidesticks for pitch & roll inputs, with passive mechanical spring/dampers providing a force proportional to stick deflection and velocity.
  • Boeing first implemented FBW in the B777. This aircraft has conventional wheel/columns for pitch and roll inputs, not connected by cables to the elevators/ailerons, but loaded by an active artificial feel system to provide feedback forces on the stick. The feedback forces are provided by a hydraulic actuator and varied according to aircraft state, resulting in similar force characteristics to earlier Boeing airliners. The B737 also has artificial q-feel in the elevator, through a system that changes the mechanical advantage of the mechanical feel spring

Note that both aircraft function the same in that they both use control deflections for inputs for the flight computers, which compute the desired surface deflection. Only the stick coupling and the feedback forces differ. From the B777 FCOM:

enter image description here

Elevator Variable Feel

The PFCs calculate feel commands based on airspeed. In general, control column forces increase:

  • as airspeed increases for a given column displacement, or
  • as column displacement increases.

The second bullet point describes a simple spring characteristic. The first bullet point means that the spring stiffness varies with airspeed, like when the elevator would be reversible and the aeroforces could be felt directly at the stick. The A320 does not have a variable spring gradient and spring forces are always the same, regardless of flight state. It is still an artificial feel though: all irreversible flight controls have artificial feel, not all of them have artificial q-feel.

To answers this question I need to remember my favourite subject, Principles of Flight - just kidding. The key to the aswer is the requirement that civil (sorry, I don't know about military, but you're also not asking) aircraft are required to have a certain amount of stick force per G. What does this mean? In simple words:the aircraft is required to require the pilot to put more force on the controls if he wants to achive a higher load factor. Even simpler: we are supposed to work hard to have fun ;)

Now we need to know what fly by wire is. FBW means that the imputs from the pilots are brought to the control surfaces, or better the actuators digital. So there is no mechanical connection between the surfaces, where the aerodynamic forces act and the controls the pilot feels. That means that there are also no stick forces per G. That would also make a pilots life very hard. I can not imagine to fly a plane without feeling it / getting a feedback on the controls.

Taking into account both facts I've listed above my answer is yes, an airliner which is fly by wire equipped needs also to be equipped with an artificial feel system.

  • Do you have any sources for the civil aircraft requirement? Is it in the U.S. FARs? Why would Airbus be exempt from this? I agree that it seems like no feedback would cause problems, but Airbus pilots seem to love how their aircraft fly. – egid Jan 10 '14 at 0:27
  • I honestly have no idea of flying an airbus, but as far as I know these aircraft are equipped with some kind of artificial feel systems. Sorry, I can't provide you with any reference to the FARs, also not to EASA, but I'm sure about the EASA rules. – Falk Jan 10 '14 at 0:33
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    Airbus controls have some give to them (the stick moves, with some resistance) but the system does not have a feedback loop - there is no artificial feel system, at least according to an article I found by some Airbus/Aerospatiale engineers... :) – egid Jan 10 '14 at 0:34
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    This should be a trustworthy source. So airbus maybe fulfilled the need for certain stick force per G by these resistance in combination with the logic of their controls - all in all the result would be quiet the same. I need to try these planes :D – Falk Jan 10 '14 at 0:41
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    Yes, what @egid said is true. Airbus fly-by-wire aircraft only have a sort of spring load system which increases the force required based on how far away the sidestick is from the centre position, so no force-feedback there. – Qantas 94 Heavy Jan 10 '14 at 2:10

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