How does the fly-by-wire in Boeing 777 differs from the Airbus system?

How does the fly-by-wire in Boeing 777 differs from the Airbus system?

Aviation Airplanes
Monday, 07 January 2008 20:08

Hi Capt Lim,

I have some questions regarding the fly-by-wire control system:

1. How does the fly-by-wire system of the Boeing 777 differs from the standard Airbus fly-by-wire system?

2. I have heard that the fly-by-wire system comes on shortly after takeoff. How long after takeoff? What altitude?

3. Why is the fly-by-wire system not put on during takeoff? It would greatly increase the safety of the takeoff.

Thank you,

Peter.

Hi Peter,

You have raised an interesting topic. Allow me to expand on it for the benefit of other readers.

1. When the Wright brothers first flew about Century ago, I believe their plane’s flying controls were achieved via strings only. Today, with the advancement of technology, computers have been used to assist the human pilot in actually flying the airplane. This was born the concept of ‘fly-by-wire’ technology which simply means that computers on the plane, transmit the pilot inputs into electrical signals through wires to actuators that move the control surfaces. Hence the name, ‘fly-by-wire’. On conventional planes after the Wright brothers, the flight-control surfaces are moved by hydraulic devices which are controlled by cables that run through the airplane.

The first flying machine to use this digital fly-by-wire concept successfully was the Lunar Module. This Module, using the concept, was able to take men from orbit to the surface of the moon in 1969 as landing a rocket on its own required a deftness and control that no human being could master. This concept was also applied on the new-generation military aircraft such as the very successful F-16 and the F-117 Stealth fighter.
Even though the military had adopted the fly-by-wire concept by the early 1980’s, the commercial sector was less enthusiastic. The argument then was that, the commercial jet did not need the agility required to fly a fighter nor did they have to worry about designing for stealth. But the fact is that, fly-by-wire concept did offer lower fuel costs and smoother flights through bad weather.

Boeing continued to the chose conventional control systems for its 757 and 767 aircraft but Airbus Industries went ahead and introduced digital fly-by-wire in its A320 airplanes. It was only on the Boeing 777 that the Company finally decided to introduce the digital fly-by-wire controls. Thus, this concept which is basically the result of wanting to put a man on the moon, have today become an accepted part of modern aviation design.

Although the Boeing 777 and the Airbus 320 series and later, adopted this new concept, there are slight differences in their applications. Airbus has taken a much different philosophical approach to using computers than Boeing. The European airplane maker designed its new fly-by-wire jets with built-in protections or hard limits.

The Boeing Company, on the other hand, believes pilots should have the ultimate say, meaning that on the Boeing jets, the pilot can override onboard computers and their built-in soft limits. The issue is, should pilots or a computer have the ultimate control over a commercial jetliner as the plane approaches its design limits in an emergency? There were strong arguments by pilots on both sides of the debates. Some pilots were of the opinion that computer protection of the A320 is very good whereas other pilots support the Boeing philosophy that they must have the final say in controlling the airplane.

Both have valid arguments. In 1995, a Boeing 757 crashed into a mountain while trying to land at Cali in Columbia, killing 159 people on board. In this accident, the warning system on board had alerted the crew that they were about to crash onto the mountain. The Captain executed a climb but forgot to retract the speed brake. On an A320, Airbus points out, the protection in the computer would have retracted the speed brakes automatically. But Boeing argues that, the jet would have hit the ridge even if the speed brakes had been retracted. Airbus planes with their fly-by-wire technology and ‘automatic protections’ have also crashed. In fact, six of the A320s have so far been lost. One of the very first A320 jets crashed shortly after the jet entered service in 1988, raising many questions about the Airbus philosophy.

The pilots were making a low-and-slow fly-pass during an air show in Habsheim, France. They were supposed to fly by with the gear down at about 100 feet. Instead, they came in at less than 30 feet off the ground. When the plane gets below 50 feet, the computer assumes the pilots are trying to land. The plane did exactly what it was supposed to do and crash-landed onto the trees! I hope you can see the difference of this system between Boeing 777 and Airbus now.

2. You are right, the fly-by-wire system comes on after the plane lifts off from the ground. It is controlled by the weight switch. How does this principle work? Well, when there is no weight exerting on it, especially when the airplane is airborne, the switch is automatically triggered on to activate the system.

3. So when the airplane is airborne, the fly-by-wire system immediately comes on. Thus, safety is not compromised. It would instantly provide any protection that it was designed to do. On the ground, with the wheel weight-switch still compressed and fly-by-wire not activated, the flight controls still move in the conventional sense, just like any other airplanes.

Hi Lim,

Thank you for the information regarding the fly-by-wire system. I just have a comment about the A320 crash record. I think it is fair to note that, 5 out of the 6 A320 crashes were because, in the beginning, pilots did not understand the fly-by-wire system well. So there were 5 accidents due to that. Since 1993, there has only been one such crash.

I think the safety of the A320 should be judged afresh since the fly-by-wire system is now understood. I don’t know if I am totally right though.

Thank You,

Peter

Hi Peter,

Since the introduction of flight deck automation, there were strings of Airbuses crashes in which misunderstanding between pilot and computer were to be blamed. The classic example, was the A320 crash at Hansheim, in France in 1988. Most pilots take time to adjust to these new concept and unless they are very current and well trained, the confusion that arise in the pilot-computer interface from the conventional, pre-automation era, could lead to undesirable consequences.
As you have rightly said, pilots today are better trained and understand the system well, so that previous accidents are not repeated. I believe that the flight deck of the Airbus 380 would have even better and safer features than the latest state-of-the-art cockpit automation we have today.

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Fly-by-wire between Boeing and Airbus
Hi Lim,

Further to your comments on the FBW systems… These systems are always active as they form the only links between the control input of the pilot flying and the control surface. It is the protection system that is activated on take off. If the FBW the system only came on when the aircraft was airborne then the pilot flying would not be able to rotate the aircraft at the required Vr speed and thus would not take off. The “weight switch” that you mention is located in the nose wheel strut and is there as a safety feature to backup the onboard computer system.

On most FBW airliners there are 4 computers, of which three are always on with one redundant. Of these systems, if one fails then the others can take over the failed computers system. So as you can see, an FBW REPLACES the hydraulic systems employed. One advantage of the FBW control system is that, if a control surface fails, like the ailerons, then the onboard computers can re-route the control input to other surfaces to produce the desired effect with out the pilot having to change the way he/she flies the aircraft. An expansion on the FBW principle is the FADEC system.

On the subject of the APS, the Airbus philosophy of total protection, while it had its teething problems, is the best in the world. You take an A320, 330, 340 up and try and crash it. If all systems are working properly, then it should stay in the air regardless of what you do to it.

Personally, if I was flying long distance, I would much rather be in an A340 than a 777 if an engine failed en-route. As that is one thing you have failed to mention, the safety aspect of having 4 engines over 2. Just so you know, I am cross qualified on, 737 classics, 777 and A320 through to A340. Of the transitions between aircraft, I found the transition from A320 to A330 the easiest as they use the same identical cockpit.

Yours
Keiron

Kieron , 01 Feb, 2008

Airbus fly by wire
I flew the Boeing – 767, retired quite a while ago, but believe that the windshear recovery maneuver was max power, and increase climb angle to feather into the stick shaker (stall warning) until recovered. I never flew the Airbus but understand that the Airbus fly by wire would preclude this recovery maneuver because the computer would override the pilot input. Doesn’t sound good to me, not to mention loss of electrics removing pilot input.
Frank Ernst , 03 Jun, 2009

Very informative article
Hi Captain, I enjoy your site and all the articles on it. Even though I have read about Fly-By Wire technology before over and over again, I am pleasantly surprised that I learned so much more about it, and how Boeing and Airbus handles it, than all other articles I’ve read combined. Thank you for this wonderful site!
GG11 , 02 Aug, 2009

avionics technician
Hi. the 777 fbw consist of 3 flight control computers 4 aces are actuator control electronics units. and 3 power supply’s.in the 777 the FCC provide the control laws. and take the pilots inputs and sends the info to the aces . the aces send the signal to the actuators. the big difference in the 777 and airbus. if theres a failure in the FCC it will go to direct mode. in other words the FCC are now out of the picture. now when the pilot puts a input into the control column instead of the signal going to the FCC it goes direct to the aces no control laws but the pilot can control the airplane. also there is a fbw disconnect switch that the pilot can use to go in direct mode.also for the person talking about the 757 crash. the 757 and 767 spoilers are fbw. and the spoilers should have retracted at the advancement of the throttles.
todd , 16 Nov, 2009

Interesting Forum guys
I know there has been mention here of crashes in the A320, but what about those in non FBW planes that might have been prevented? Sure the AA 757 that crashed in the mountains might be one – I guess there is some dispute about that.

What about the Sioux City DC-10 that lost its hydraulic controls when the #3 engine fan blade severed the hyd lines?

What about any of the numerous boeing crashes caused by pilots exceeding the flight envelope without even knowing it – the China Airlines 747 that nearly plunged into the pacific (“1 G all the way down”) when the pilots didn’t step on the rudder after an engine failure? The 737 that crashed after takeoff from Sharm al Sheik because the captain became disoriented? The Adam Air 737 that spiral dived when its crew didn’t hold it level after initiating a change in autopilot mode?

Another fascinating angle is situations where a blocked pitot sends faulty readings to automated systems, which I believed spelled the demise of one Birgen Air 757. Was that not also discussed as a possible cause of the as-yet-unsloved air France crash last year? What if a pitot became blocked with ice – would the flight computers not them believe the aircraft was traveling too slowly and initiate either a power up or nose down? Is it possible the “hard limits” prevented the pilots from overriding the computer in such a situation?

Thanks!

Nate , 07 Jan, 2010

FBW and cable backup
My understanding of both the 767 and 777 models is that while FBW is considered the primary flight control system with electric- hydraulic actuators on al the ‘ feathers’ , etc, there is still a minimum control capability using cable control to trim tab- servo tab- inboard- outboard ailerons, etc to some of the ‘ feathers’, allowing at least some manuving capabilityy when everything else turns to *****.

It is and has been the philosphy of BA that in the end, the pilot has ULTIMATE AUTHORITY.

That being said, does anyone know if the 787 also has minimum cable control- trim tab – servo tab built in ?

ARBE , 29 Mar, 2010

Your site’s look and feel
Dear Captain Lim,

I just discovered your site, and I love it! Questions seem to be asked in the earnest desire to know more, and you do a wonderful job of explaining quite complex things in ways that can be understood. Everybody seems to be respectful and courteous — not like other sites where people are practicing a word war, trying to show how intelligent they are and how stupid the other posters are! The posts are longer than on many sites, but that’s because you take time with the explanations and do it right.

Thank you so much.

Griff , 29 Jun, 2010

Your site’s look and feel
Hi Griff,

Many thanks for your complimentssmilies/smiley.gif

Captain Lim , 29 Jun, 2010

FBW SYSTEMS LIMITATIONS
I would like to add my two cents to this discussion. I do believe that the flight deck automation makes flying much safer, and certainly there have been instances in which pilot error (due to the stress of being in one of these conditions one makes inadvertent mistakes) actually worsened the situation and resulted in a crash. However there are also limitations to the system as witness the crash of Air France 447. Although it will be argued that this is still an unsolved investigation, it is never the less true that the FBW is totally dependent on the pitot-static system, an if this system becomes compromised the Automated system is then confused and starts shutting down vital systems leaving pilots totally confused as to what to do with multiple warnings going on at the same time, and the Flight Deck Automation (yes even on airbus aircraft) will disconnect, sort of “well this is all I can do so over to you, bud, good luck”. So I do believe that full automation will make pilots unacquainted with actual flying and come one of these situations they will not be able to save the air plane. So all I’m saying is that I do believe there has to be a middle ground between machine overriding humans and humans overriding the machine. And pilots need to do actual flying without relaying on the automated systems every once in a while to stay sharp and be able to actually fly the plane should all these systems fail.
Jeff , 03 Jul, 2010

Marty
Hi all. Lots of comments which have covered the main aspects of electronic control. Call it what you like, NORMAL LAW, ALTERNATE LAW, ACARS…..its still electronic. This has a lot to do with the early Airbus crashes aside from the gear down problems the following can be taken as humerous but seriousy side sticks are for games. As with the 777 we will just have to see over time. By the way the first Airbus that crashed into the trees. The pilots started at over 100 feet but the gear down did put it in landing mode and started to drop the height. The pilots did overide the system but it takes 7 seconds to spool up the engines in that aircraft and too late! The pilots were jailed and mysteriously 4 seconds of CVR tape “was lost”. Why? any new aircraft being displayed at an airshow of the first model crashing affects a huge investment for governments and manufactures, and blaming the pilots and the CVR transcript saved Airbus. Airbus immediately changed their manual. How do I know this? Someone very close to me worked on the first Airbus. The A380 seems to be going well despite a few minor teething problems that all new aircraft go through so for both Airbus and Boeing happy landings.
Martin , 05 Jul, 2010

Actual Flying
I agree with the person who said that a pilot might have to fly other aircraft or practice outside of the job just to keep experienced with actually flying by the seat of his/her pants. One thing though, can anyone try to explain how the fly-by-wire computers would have operated or aided the a320 that went down in the hudson. I mean how is the computer going to react to both engines failing and what will it do to the control surfaces?
Luke , 04 May, 2011

Retired
A Gulfstream 650 test flight at Roswell New Mexico recently ended in tragedy. Can someone compare the fly by wire system on that plane to the systems on Airbus and Boeing? Thank you.
Bob , 04 May, 2011

re actual flying
WRT to the A320 in the Hudson, all turbine AC have a RAT (Ram Air Turbine) that automatically pops out the side when power is lost. It’s a little windmill that creates enough power to maintain control at all times. The Hudson A320 had control all the way down into the water, otherwise they would have landed in lower Manhattan like a lawn dart.

The 787 tested its RAT a few months back when the flight test aircraft had an electrical panel fire. All FBW aircraft are reliable in that regard; FAA and EASA require several demonstrations during flight test.

cmm , 26 May, 2011

Alteration
Sear Captain and All,

Still dont know that structurally what is the difference between B777 FBW system and regular Airbus ones…
777 has control wheel but Airbus has sidestick, so there must be a deeper difference than “philosophy”

Gergo , 30 May, 2011

the difference between control wheel and sidestick
As far as I know, the main difference between Boeing and Airbus is based on the philosophy. For Boeing, the pilot is the great master on board , and for Airbus ,it is computer who takes the final decision.And the difference between sidestick and controlwheel is that there is a mechanical link between the two controlwheel.That help to avoid that two differents orders are given by the pilots to the computer. Anyway, the philosophy to try to replace the pilot by computers will never be the right one. But giving the pilot the maximum assistance by the mean of computers will increase of course the safety of the plane.
tsamoun , 26 Jun, 2011

Airbus Fly by wire
There’s an accident on Brasil occoured in July 17 2007 caused by an “error” on Fly By Wire.

An Airbus A320 from TAM Linhas Aereas (“TAM Airlines”) with a single trust reverser working (the left one) couldn’t stop due the Fly By Wire assuming that the pilots wasn’t landing. So the airship didn’t brake and have accelerated the right engine, turning left, overraning the runway and crashing against a gas station and a TAM Express building (from the same company) in the outside of the airport. It killed everyone on board, and a lot people in ground too.

This is the worst brazilian air crash. Absurdly the pilots was blamed by the accident, of course, Airbus always do this. But everyone knows was a FBW problem.

http://en.wikipedia.org/wiki/TAM_Airlines_Flight_3054

Timm Guy , 27 Jun, 2011

Blame
Timm Guy: What you say of course applies to both Boeing and Airbus or heck every single company that makes aeroplanes or for that matter most products. They’d much rather someone else is at fault the a flaw in their product. That’s why we rely on independent investigators, which in this case as in a number of cases included the US NTSB (who from their history don’t appear to be afraid of speaking out if their conclusion is rejected by the other parties involved). I’m not saying the system is perfect but where there are flaws you can be sure both manufacturers take advantage of it.
Nil Einne , 03 Nov, 2011

Automation Between Airbus and Boeing
Hi to all,

Fly-by-wire is a system that replaces the conventional manual flight controls of an aircraft with an electronic interface.

Airbus and Boeing has the same fly by wire system with different Automation.

smilies/grin.gifsmilies/grin.gif

Pao , 24 Nov, 2011

re: the difference between control wheel and sidestick

…And the difference between sidestick and controlwheel is that there is a mechanical link between the two controlwheel.That help to avoid that two differents orders are given by the pilots to the computer…

Just-released analysis of the recorders from Air France Flight 447 indicate that indeed, differing inputs from the pilot and co-pilot essentially led to the worst crash in Air France history.

Robert , 20 Dec, 2011

Cooperative control combining strengths of man and machine
I think AirBus went overboard in delegating too much responsibility to the FBW while excluding the human’s superior situation awareness. As I predict the Air France 447 Final Report (due July 5) will show, the AirBus philosophy puts the pilots in a powerless situation, leading to boredom and retreat from engagement. When a “situation” develops, the pilots don’t know where to “plug in”. A better HMI design would keep the pilots in charge, and let them delegate to the machine, but maintain engagement and workload the entire flight except during breaks. The FBW can process sensor input much more rapidly than the pilots, so it makes sense to let the FBW “talk” to the pilots and recommend what it sees as the best way to handle a fault, along the lines of a smart, interactive operations advisor. It sounds like a great project for a HMI Design class. The relative strengths and weaknesses of human and machine dictate how a cooperative partnership should be designed.
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  12. FBW effectively puts control of the aircraft in the hands of a nerd like me who wrote the software rather then the pilot. It works great as long as all systems are go. But it is impossible to anticipate every mechanical failure (engine failures, undercarriage stuck half retracted, overstressed rudder breaks off etc) that could happen and have software pre-written for each case – assuming even that the computer could correctly identify what had happened. I spent a lot of time working on an adaptive autopilot that was supposed to automatically learn the control characteristics of a vessel, only to conclude that the whole theory was rubbish for the following reason: An autopilot spends 99% of its life holding the vessel on a straight course. The reason heading deviates is not because a control surface was moved, it is because of headwinds/turbulence/weather. The autopilot then moves a control surface to correct the deviation. So cause and effect are reversed, which causes the math to blow up.
    Therefore ultimately in an emergency the pilot should be able to impose his will on the control surfaces, the engines and the landing gear by hitting a big red knob to gain total control..

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