Fri Aug 31, 2001 9:39 pm

I am just wondering about fly-by-wire used in today's modern airliners. As a university student studying aviation, i have no hands on experience with this type of thing. To my understanding it involves a control input by the pilot activating wires of which electronic pulses are computed in a central computer. The computer judges if the control input is relevant or not and activates the hydraulics to move the control surface.

In a conversation with another student at uni, we were both of different opinion on which aircraft use fly-by-wire. Having known that it is used by airbus, we were undecided if it is used in Boeing as yet and were quite certain that it used in the 747 for their engine use.

I was just wondering if any experienced pilots could shed some light on the subject for me and which aircraft today are using fly-by-wire.
Any help would be appreciated

Thank you.
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RE: Fly-by-wire

Fri Aug 31, 2001 10:10 pm

The 777 is a fly by wire aircraft. It uses the ARINC 629 serial bus standard throughout the airframe. It connects all of the LRU avionics boxes together. There are 3 redundant buses. In the flight deck the ARINC 429 connects some systems and this may be used on other Boeing airframes. The 629 system was developed in the late 80's / early 90's for the 777. I would guess the the new Boeing Sonic Cruiser design would use the same system, but the 777 is the only current Boeing aircraft with it in use.
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RE: Fly-by-wire

Fri Aug 31, 2001 10:47 pm

ARINC is a communicatiosn medium. All of the communications (interfaces) btwn LRUs on an aircraft such as the B777...use an ARINC digital databus to talk to one another.
But that does not define Fly-by-wire.

On an aircraft such as the 737, the flight control system is mechanical. It is hydraulically assisted...but mechanical nevertheless. For instance, when the pilot makes an input to the control wheel for roll, cable on the ctrl wheel provide an input to an aileron PCU (power control unit). The power control unit which is hydraulic through mecahnical connection via cable the aileron...moves the aileron. On the 737 u can, if u lose hydraulics, fly manual reversion...which is down to the old stuff...flying via tabs and stuff.

Now that we understand that, we can understand Fly-by wire. Take away all the cable and any mechanical connections now. When the pilot makes an input to the control wheel, a transducer (position sensor) measures the amount of travel of the control wheel and sends this information to a box. The box then processes this and sends it to anotehr box which then sends this information to the aileron PCU. The aileron PCu - still hydraulic powered then allows hyd pressure to whichever side will complete the command. You lose electrics, you lose your control of the aircraft. There is no manual reversion as such in a 737. But they have made that aircraft so redundant - it is hardly something to even fathom.

FBW technology is hardly new for Boeing though. The 757s have used it for years in there spoiler control sys.

Hope this helps

RE: Fly-by-wire

Fri Aug 31, 2001 10:54 pm

Thanx for that, it helps me out a lot!!!
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RE: Fly-by-wire

Sat Sep 01, 2001 12:42 am

ARINC stands for Aeronautical Radio Incorporated. They just use the name "ARINC Incorporated" now. Among other things, they develop standards for avionics systems. The standards include information on installation, wiring, data buses, databases, and general guidance.

Some even define the size of LRUs and the electrical interconnects. You can get additional information at

ARINC....not just data busses!

leigh pilgrim
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RE: Fly-by-wire

Sat Sep 01, 2001 3:44 am

Speaking of Fly by Wire, would'nt you of thought that the 767-400 would have had it?


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RE: Fly-by-wire

Sat Sep 01, 2001 4:36 am

The 67-400 is a stretch of the existing 67-300, with other changes like taller landing gear and heavier structures. It would be very difficult and expensive to change an AC designed with mechanical, hydraulic controls to a FBW design. Although the 47-400 is a radically different airplane than the -200 / -300, because of the advanced flight deck, "engineering" out the flight engineer, it still uses the mechanical flight control system of the earlier designs. I believe Airbus used FBW technology in the 320 series as well as the 330/340 and most likely the new 380.
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RE: Fly-by-wire

Sat Sep 01, 2001 1:51 pm

Geebar's original post asks whether the 747 has digital engine controls. This is different from "fly-by-wire". It is called the FADEC (Full Authority Digital Engine Control) and most late-model a/c use it, whether they utilize FBW or not. This system takes the throttle position command and sends appropriate signals to the engine fuel controls.

"In God we trust, everyone else bring data"

RE: Fly-by-wire

Sat Sep 01, 2001 4:08 pm

Thanx people for your feedback,
This sheds a lot of light on the subject and i now feel i have a better understanding of fly-by-wire.

If anyone would like to add any further comments i would be glad to hear them, as i find this subject quite interesting.

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RE: Fly-by-wire

Mon Sep 03, 2001 3:18 am

Concorde has a 'hybrid' FBW system, the control column sends an electrical signal to the hydraulic actuators that move the flying-control surfaces. Because of this, artificial 'feel' is maintained.
There is also a back up conventional control system.
The side-stick later used on A320 series and A330/A340 was first tested on a modified Concorde, (A/C 201).
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RE: Fly-by-wire

Tue Sep 04, 2001 5:41 am

One last query on this end. Rather than start a new post...

yesterday I as at the bookstore looking for a good aviation book and as I read one, it mentioned that the L1011 was the first(or one of the first) to incorporate such techonology. Is that true?

I remember a post not to far back stating with A/c first went into production with FBW.
Anyone please tell me?
Forum moderator 2001-2010; He's a pedantic, pontificating, pretentious bastard, a belligerent old fart, a worthless st
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RE: Fly-by-wire

Tue Sep 04, 2001 6:34 am

FBW is a lot more than just an electronic "connection" between the control handles and the control surfaces.

The Airbus and Boeing FBW philosophies are rather different, and the following fits best on "busses":

A lot of other inputs are fed into the control computers, airspeed, angle of attack etc.

Adverse yaw compensation is automatically calculated, so the pilots doesn't need to touch the rudder pedals until he lands in crosswind.

Drooping ailerons are a pure software issue.

The sidestick control should be regarded more as "give me so and so much bank angle or climb/descend rate" than an connection to the ailerons and elevator.

Software prohibits overstressing the airframe and limits bank angles.

Autothrottle is intergrated in the system.

Airbusses have a very rude mechanical way of bringing a plane down in case of total FBW failure. It has wires to the rudder for yaw and roll control. Also differentiated engine power can control yaw/roll. Mechanical trim on elevator, and to some extent symmetrical engine power, can control pitch. But it is a very tricky job to hit a runway that way. In practice the two pilots will share the job, one taking care of the pedals, while the other one takes care of pitch. That's at least how they practice in sims. Then they pray for nice weather, no sidewind and a loooong runway.

The A380 will not have any mechanical backup since:
1. It is really only waste of good metal for the wires.
2. No human pilot would have the power in his legs to turn the rudder.

FBW should no longer be looked upon as some "extraordinary" control system for airliners. During the last fifteen years no totally new large airliner design has left the drawing board without having FBW control. And it will never ever happen again. The B767 will walk into history as the very last large airliner with mechanical controls designed on this planet.

Best regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs
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RE: Fly-by-wire

Tue Sep 04, 2001 8:39 am

Mirrodie --
yesterday I as at the bookstore looking for a good aviation book and as I read one, it mentioned that the L1011 was the first(or one of the first) to incorporate such techonology. Is that true?

I think the L-1011-500 was the first to have a digital Flight Management System (FMS) - it was (I believe) for navigation and fuel management. However, it was not the true digital link between the control inputs and the actuators that we refer to as FBW. My memory is weak on this, and I don't have time to look it up.

"In God we trust, everyone else bring data"
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RE: Fly-by-wire

Tue Sep 04, 2001 9:44 am

What type of mechanical backup system does the 777 have?

(I know how the 1's and 0's get around the aircraft but not not much of the mechanical)

Also, what are the differences in philosophies in the FBW systems between Airbus and Boeing

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