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Home > Airplanes > 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.

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. It seems 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! However, according to the captain after the incident, there were issues with the radio altimeter and power acceleration which was not made known to them by the company..

2. The fly-by-wire system comes on after the plane lifts off from the ground. On the Boeing 777, 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 B777 is airborne, the fly-by-wire system immediately comes on. However,
on the Airbus A330, the normal FBW control law comes in when the pitch is more than 8 degrees up and 8 seconds after lift.Thus, safety is not compromised. It would instantly provide the safety protections 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. Similaly, the Airbus A330 goes to conventional mode (direct law) 2 seconds after touch down and less than 2.5 degrees nose down.

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 , Low-rated comment [Show]
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 , 02 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 , 02 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.
PB in CA , 15 Jun, 2012
Issues relating to the disappearance of Flight 370
Assume flight 370's avionics systems were compromised (by competent engineers with physical access to the Primary Flight Computers). Would a 777 pilot realize the ACARS system was not operating? In other words, if the avionics did not report a fault would the pilots necessarily detect it some other way?

2.
Campbell , 18 Mar, 2014
Well, that's wrong...
Hello, when you're talking about the difference between Boeing and Airbus, the fact is there is almost none today. Both Airbus and Boeing pilots can turn off the protection (for Airbus, by putting the aircraft in "direct law").

When you're talking about the A320 crash, that's just wrong, the computer did not put the aircraft in landing mode. That's what the pilot say because he didn't want to have any responsibility in this crash. But it has been proven that the computer did save a lot of person on board that day.
The pilot try to do a "go around" and put full throttle, and so did the aircraft. But because of the stunt he was doing, the aircraft was at the limit from stalling. So the computer activate the stall protection, prevent the aircraft from stalling. And if he didn't manage to climb soon enough (it was just impossible for any aircraft) he did save the passengers by "landing" on the trees instead on crash violently after a stall.
This crash did in fact prov that the stall and other protection on modern airliners are efficient.

And all the Boeing aircraft made since the launch of the A320 (so, the B777 and the B787) use the same philosophy. The only difference? Boeing use a joke, Airbus a side-stick. (And Boeing cockpit are brown, Airbus cockpit are blue).
smilies/wink.gif
dufonrafal , 06 Jun, 2014
Right
Dufonrafal, your right. how else does everyone think airbus test pilots fly at airshows. Airbus fly's displays in direct mode, which has total disability of all protection or computer input. it's just like the surfaces are hard wired, and hard wires are 1000times less likely to fail that hydraulics:-)
Stan , 28 Jul, 2014
MH370 Tracking and the Characteristics of the 777's Active Flight Control System
Once the oxygen flare fire of 15 to 20 seconds erupted in MH370's cockpit, a number of systems were affected by the melting of plastic pushbuttons (and their housings) on exposed consoles. Some keypads fused, some circuit-breakers tripped thermally and some LED screens melted and sagged. However the active Flight Control system on the 777 is totally unique. That ACT-FCS has redundant redundancies.
Even though one or both pilots' lungs may have been seared by the oxygen flash-fire, one of them was still capable of instantly selecting a reverse heading to Pulau Langkawi. At some point during that turnback, the oxy blowtorch caused by the copilot's regulator's LP hose melting (per Egyptair's SU-GBP on the Cairo ramp over 3 years earlier), weakened the side fuselage (see imagery from Egypt's report linked at
http://tinyurl.com/or9bzf2 ). With the assistance of the 4.5 psi cabin pressurization differential pressure, the cockpit sidewall ruptured outwards causing a rapid depressurization and the aural alarm.
So the pilot flying disconnected the autopilot, "stuffed" the nose down, but didn't manually trim it nose-down (777 pilots very rarely touch that manual trim wheel due to autotrim - i.e. it's easily forgotten). When he then passed out due to hypoxia and lung-searing (mask on, but no oxygen left), he relaxed the fwd pressure on his yoke and the aircraft pitched back up into a zoom climb, sealing the fate of all onboard. For the next seven odd hours, the MH370 ghost ship flew on, not on autopilot but control being maintained by the flight envelope protection built into the 777's ACT-FCS and the aircraft's inherent stability. In essence, a 777 not on autopilot will instantly pick up a dropped wing and (in pitch) will maintain its trimmed speed due to a very well damped phugoid. Its heading will remain static plus or minus only a few degrees of heading - so its mean line of advance tracking into the Southern Ocean was quite apparently "autopiloted" - even though it was not.
As the aircraft headed south and burnt off fuel, it would have constantly climbed, greatly improving its range. Why the tracking changes after it overflew the Malay Peninsula? It simply flew into some thunderheads (ITCZ being north of the Equator at that time of year) and got spat out on a new heading, following its encounter with heavy turbulence. Once south of the equator and clear of the InterTropic Convergence Zone (and its 50,000 foot tall thunderheads), it would have been flying in quite calm air and climbing through 40,000ft due to the fuel burn-off trim change. In a 777, a ghost flight capability is quite coincidentally "built-in" - via the characteristics of its ACT-FCS.
One of the immutable rules of aviation is that most accidents have a precedent that, if not addressed, will eventually recur. Obviously nobody extrapolated what had happened (on the ramp at Cairo to SU-GBP) into an airborne context. The airborne variant was always going to be quite different due to pressurization and the immediate loss of the oxygenated cockpit environment once the cockpit sidewall blew out (due to the blowtorch effect of the oxygen fire at source). What may have caused the oxygen to erupt at that point? If one pilot announces his intention to leave the cockpit on a toilet break it used to be "de rigeur" (i.e. SOP standard) for the other pilot to haul his oxygen mask out of its housing and don it. The original problem (an electrically conductive stiffener wire running internally within the LP hose to stop kinking) was probably still there on the MAS 777's. Only US registered airplanes are affected by FAA Airworthiness Directive mandates to modify equipments. As recently as October 2014, the FAA's AD's were still playing catch-up with Boeing airplanes still equipped with the lethal hoses.
John Sampson , 08 Oct, 2014
Boeing 737-800NG
Why B737-800NG is not Fly by Wire System? It is latest model then why?
Saurabh , 10 Oct, 2014
Private pilot
I wold never put fly by wire system in a small plane with small side stick the orginal direct cabels are much saver and simpler.
Kristján Ómarsson , 29 Mar, 2015
B777 FBW (PFC) not active on Takeoff
HI,

The B777 uses ADIRU and SAARU accelerometers for their computations.

Due to vibrations during the ground run these signals are contaminated and cannot be used. That is why the PFC only kick in when airborne.
Karl Montens , 17 May, 2015
Mr
This debate cannot really be resolved by simply looking at it from a "technological" perspective. The fact of the matter is humans can, and do, make mistakes and so do computers, accidents will continue to occur with either. Some of us don't like it, makes us feel useless, helpless, but the odds probably favor the computers.
JoeLemo , 30 May, 2016

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