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If the control system in an Airbus is fly-by-wire, then what is the control system in Boeings? How does it work? What are its general differences from the fly-by-wire?

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    $\begingroup$ @JanHudec your answer comes closest but I'm not sure any of the answers there really address in enough detail what is being asked here. $\endgroup$ – fooot Oct 6 '15 at 19:29
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    $\begingroup$ Short answer: Boeing is to fly-by-wire too $\endgroup$ – Him Oct 6 '15 at 21:16
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    $\begingroup$ This isn't a meaningful question. Airbus introduced fly-by-wire on the A320, so the A300 and A310 had conventional hydraulic controls. Boeing are credited with producing the first modern airliner - the Boeing 247 - back in the Thirties, which I think I read somewhere had mechanical control linkages, while the 787 is a fully electrical fly-by-wire system. Intervening models use hydraulics, and later versions of earlier models (like the 737) started with hydraulics and have had fly-by-wire added later. You need to be more specific. $\endgroup$ – user11516 Oct 6 '15 at 22:35
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Boeing uses a more direct approach to control (but both systems have warnings). In short it boils down to who has final authority of control surface actuation. Fly by wire does not just mean that control surfaces are controlled electronically (even the Cessna 172 has electric flaps) but that a computer in some way takes the pilot (or pilots) inputs and generates a control surface output. In the airbus case the computer has the final say, so if the pilot commands the plane to do something it should not, the computer will not move the control surfaces and allow it to enter such an attitude or speed. Boeing takes the reverse view and gives the pilot final authority so what ever control inputs are made translate to control surface movements.

With that in mind Boeing does have things like a yoke shaker in the event of approaching a stall and a yaw damper etc. Airbus will allow full control surface actuation with Direct Law however the plane is not normally in this mode. Boeings Standard protections and augmentations is similar but will allow the pilot to enter the conditions

"...to inform the pilot that the command being given would put the aircraft outside of its normal operating envelope, but the ability to do so is not precluded." (source)

On the contrary vertical stick motion in an airbus in flight actually controls load factor and not necessarily pitch directly. So its always some form of proportion to the aircrafts speed.

If memory serves Boeing control surfaces are set up such that movement of one yoke will move the other yoke in tandem, likewise they can not be simultaneously moved in opposite directions while airbus controls can be moved in opposite direction and the computer will summate the inputs (although an override button is present on each stick to disconnect the others should something be improperly acting on it).

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  • $\begingroup$ I would argue that the 172 has electric flaps, not electronic. There's no logic, just pure electrical signal. FBW implies a flight control computer in there somewhere. $\endgroup$ – egid Oct 7 '15 at 3:27
  • $\begingroup$ A bit of semantics, but edited to reflect. $\endgroup$ – Dave Oct 7 '15 at 3:27
  • $\begingroup$ This whole question seems to be about semantics! ;) $\endgroup$ – egid Oct 7 '15 at 3:41
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Using a pure definition of fly-by-wire, both Boeing and Airbus airliners can be considered fly-by-wire.

tl;dr:

  • Boeing has built some FBW airliners (777, 787) and some that aren't (707/720, 737, 747, 757, 767).
  • Airbus has built some FBW airliners (A320 series, A330, A340, A350, A380) and some that aren't (A300, A310).

long version:

Fly-by-wire (FBW) is a system that replaces the conventional manual flight controls of an aircraft with an electronic interface. The movements of flight controls are converted to electronic signals transmitted by wires [...], and flight control computers determine how to move the actuators at each control surface to provide the ordered response.
Fly-by-wire, Wikipedia

With that description in mind, both manufacturers build FBW aircraft. Pilots' control inputs are translated into aircraft flight control surface movements by a set of redundant computers.

Boeing's first FBW airliner was 1994's 777, and their only other pure-FBW design is the 787. The 748 is a partial-FBW design. Both the 777 and 787 have some computer-enforced limits in place to keep the aircraft within the flight envelope, but those limits can be overridden, and the aircraft generally are said to 'feel like a normal airplane'.

Airbus's first FBW airliner was the 1987's A320, and all their subsequent designs are FBW. Airbus's control logic is much less direct than Boeing's, containing full flight envelope protection in the 'Normal Law' configuration, and correspondingly less protection if the aircraft reverts to 'Alternate Law' mode (which is roughly comparable to Boeing FBW). None is provided in what is called 'Direct Law', where the computers simply pass commands directly to the flight control surfaces.

That said, both manufacturers build fly-by-wire airliners

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  • $\begingroup$ Actually, Airbus' “alternate law” is nothing like Boeing's FBW. Airbus flight laws are “cooked”—you tell the computer the desired pitch- and roll-rate and the computer does it. If you release the stick, the plane will fly straight; no fiddling with trim. That applies also in alternate law, just the protections are switched off. Boeing's flight laws are “raw”—they emulate mechanical controls with trim and everything. $\endgroup$ – Jan Hudec Feb 15 '17 at 14:36
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Boeing is to fly by wire as Airbus is to fly by computer, would probably be closer to the mark.

Both are fly by wire, but Boeing is closer to direct input - I move the yoke halfway to the limit, the controls move halfway to their limit

While Airbus is a suggestion to the aircraft as to what you'd like it to do - I move the side stick halfway to the limit, and the plane performs that action at something like half the rate the performance envelope should allow.

Sort of.

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  • $\begingroup$ Not sort of, it's quite accurate. Boeing emulates mechanical input faithfully except it will increase resistance if you reach the flight envelope limit. While in Airbus, full forward deflection means load wings to -0.5G, full aft deflection means load wings to 2.5G, full right deflection means 25°/s roll rate right, full left deflection means 25°/s roll rate left and stick center means 1G and no roll rate. It's not a suggestion though, it's an order; the plane will do it unless it would take if beyond the flight envelope limits (but the Boeing one protects against that too). $\endgroup$ – Jan Hudec Feb 15 '17 at 14:45
  • $\begingroup$ The "sort of" was relating to the fact that Boeing isn't 100% direct input, and that Airbus has a mod which is closer to direct input, so neither system is entirely analogous to direct input, fly by wire, or fly by computer. It's about right, but can be a little fuzzy depending on the exact circumstances $\endgroup$ – Jon Story Feb 22 '17 at 13:06

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