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Fly-By-Wire Contributed To Air France 447 Disaster
Hugh Pickens writes "The Telegraph reports that although fly-by-wire technology has huge advantages, Airbus's 'brilliant' aircraft design may have contributed to one of the world's worst aviation disasters and the deaths of all 228 passengers onboard Air France Flight 447 from Rio de Janeiro to Paris. While there is no doubt that at least one of AF447's pilots made a fatal and sustained mistake, the errors committed by the pilot doing the flying were not corrected by his more experienced colleagues because they did not know he was behaving in a manner bound to induce a stall. The reason for that fatal lack of awareness lies partly in the design of the control stick – the 'side stick' – used in all Airbus cockpits. 'Most Airbus pilots I know love it because of the reliable automation that allows you to manage situations and not be so fatigued by the mechanics of flying,' says Stephen King of the British Airline Pilots' Association. But the fact that the second pilot's stick stays in neutral whatever there is input to the other is not a good thing. 'It's not immediately apparent to one pilot what the other may be doing with the control stick, unless he makes a big effort to look across to the other side of the flight deck, which is not easy. In any case, the side stick is held back for only a few seconds, so you have to see the action being taken.'"
And then we send robots down to gather the black boxes that recorded all the flight data.
Ever think we're relying a little too much on technology these days?
This topic has been beaten to death by professional pilots and aviation experts on pprune.
...but rather it was a lack of force feedback. And that technology has existed, even on the consumer level (and no reason it can't exist at the airliner level that I know of), for many years.
When i read the annotated black box transcript a few weeks ago, i asked airplane experts about this. They told me:
If one pilot pulls and the other pushes the stick, there is an optical and audio signal.
Also the person was questioned if he pulls the stick and he confirmed it. Unluckily it was already too late by then.
I am no expert, but the root cause was IMHO the crew ressource management and training problem.
Did the same person write the title and the summary of this story? Fly by wire has nothing to do with the control stick and everything to do with how the control inputs are sent to the control surfaces; some control schemes simply permit some cockpit/stick design decisions that in turn led to what the story is actually talking about... Though, you know, I think they should go back to lever & cable systems, then the pilot wouldn't be able to stall the aircraft because he'd never be able to exert enough force to pitch up. :P
Even as you read this, your pants are strangling your loins! Aaa!
I wondered why the pilots didn't respond to a stall by instinct. The feel of the plane should have been a major clue that something was wrong with their course of action. A lack of feel in the FBW system would certainly be a contributing factor in this kind of situation.
When all else fails, run.
The co pilot surrendered control of the aircraft to his colleague!
The problem described in the summary has nothing whatsoever to do with fly-by-wire. Yes, there may be an opportunity for improvement in that there should be some force feedback from one stick to the other. By that does not mean the plane can not be flown by wire. Plus, the fundamental issue in this accident is an operator mistake not corrected for by the other people present. I.e. it's a crew training & management issue.
Just in case this is a Boeing fan doing some Airbus bashing: Boeing is using fly by wire as well in the 777 and later designs.
Reporters are professional trained in how to write. Surely they should learn the use of this logical fallacy?!
It wasn't mechanical feedback that was lacking. The crew should have communicated better.
The sticks dont follow either ie if rhe copilot pushes forward the pilot gets no feedback on his stick this is happening. This was an issue here not fbw itself.
Other factors at play also of course
While there is no doubt that at least one of AF447's pilots made a fatal and sustained mistake, we still will blame the competitions system, so that they will buy ours and not theirs.
Don't get me wrong, Airbus would do the same. Or at least all of the governments involved.
Don't fight for your country, if your country does not fight for you.
Crass regionalism is a global phenomenon.
Are you under the impression that The Telegraph is an American publication?
Where's the editorial control today? How did they sneak this obvious industrial hit-piece past the editors? Didn't have your coffe yet huh?
And as there are mostly americans here on slashdot people will be only too willing to drink to anti-European kool aid.
I expected better from slashdot.
Ye gods, what a horrible realization.
FWIW, I also bash Boeing at every opportunity presented to me, then create a few opportunities on my own for good measure.
I wonder if there was an Airbus engineer who had suggested mechanical feedback linking the sticks, was overruled, and now feels vindicated. And if so, I wonder whether the culture at Airbus will cause him to be promoted or to be fired.
Read it ALL on pprune (ignore the permanent troll there), and you'll see that things were quick, but not necessarily simple. The sad guy who just 'pulled' to misleading 1g stall had his young wife in the back, so don't ever think he wasn't trying. I do believe think the sidestick movement (lack of) and logic (deltaT, not proportional) is suboptimal, but that wasn't all.
Red herring #1: This isn't news.
--Maybe not to some of us. But TFA is new, and in a more general publication than the sources many of you have cited.
Red herring #2: This is an American anti-Airbus hit piece.
--Probably not. The Telegraph is a UK publication, and the title seems deliberately designed NOT to call out Airbus. See #3...
Red herring #3: The title blames FBW, that is a separate issue from back-driven controls.
--Quite right. Perhaps the author wished to avoid seeming anti-Airbus; perhaps he just wasn't precise in his phrasing. You sure don't have to read far to find out the truth.
Red herring #4: This is bullshit. The pilots fucked up.
--Perhaps you're not familiar with the English phrase "contributed to." It doesn't mean the same as "caused." In any safety-critical occupation, a piece of equipment that obscures the actions of one of the team members impedes the type of cross-checking that was a major reason for using a team in the first place.
No system is perfect. People are perfectly free to say that they think this is a minor issue which will only come up in very rare circumstances, more than compensated for by merits of the side-stick. Others might argue that the risks outweigh the benefits. I am smart enough to know that I am not qualified to have an opinion on the issue.
I'm just tired of the hysteria here.
a big effort to look across to the other side of the flight deck, which is not easy
Now, it's a long time since I've been on a flight deck, but they weren't that big. What's changed so much that it's such a huge imposition for someone to look at the guy in the other seat and see "oh yes, he's pulling back on the stick" and then maybe slap him around the head until he stops.
politicians are like babies' nappies: they should both be changed regularly and for the same reasons
Yanks sure like to bash Airbus at every opportunity.
Ever since that first demo flight ended in a fiery crash because of a flaw in the fly-by-wire system, some people have been nervous about it. Funny how that works ;-)
Could somebody please translate this wonderful collection of words into English?
But the fact that the second pilot's stick stays in neutral whatever there is input to the other is not a good thing.
It seems like an important sentence, but I have no idea what it means.
I don't respond to AC's.
No relation I assume?
in my opinion the biggest issue was that the pilots weren't aware of the huge angle of attack (AOA) that they were maintaining, and AFAIK they didn't have an AOA indicator in the cockpit. it was also dark and in a big storm, thus there were no external references.
they had the plane pitched up about 10 degrees, which is not that big. they also had speed - they were close, but not below stall speed. but at the same time they were falling badly, which meant their angle of attack on the wing leading edge was at least 30 degrees if not more.
remember that the basic reason of a stall is always high AOA - not speed, not pitch, but high AOA.
of course, you 'should' be able to put it together - high pitch, large negative vertical speed -> high AOA. it seems the young co-pilot didn't. :(
Last year I watched a special on a TV network about this tragedy. I can't remember if it was History, Science, etc. But they had shown that there was a very good chance that all of the speed sensors on the plane had frozen over with ice. Those speed sensors are critical to the operation of a fly by wire plane regardless if it's being flown manually or by auto pilot.
I'll try to find the video or transcript because it was a very well thought out scenario of what likely happened. The experts on the show said there wasn't much the pilots could do if the sensors had actually frozen over.
"A plan fiendishly clever in its intricacies"- Homer Simpson
http://en.wikipedia.org/wiki/Fallacy_of_the_single_cause
nuff said. hysteria over.
They did get stall warnings, but only when they (briefly!) tried to put the nose down a bit, early on in the transcript. Pulling the nose back up, the stall warning went away - the plane's stall warning couldn't work at such low airspeeds or AoA (angle of attack).
So they had an alerting system that responded counter-intuitively. Pulling the nose up into a deeper stall actually made the stall warning go away. I've read on pprune that many pilots consider that if commercial airliners had AoA displayed in the cockpit (plus the training to use them) - apparently modern aircraft are already measuring AoA, it's just not displayed - it would be a far less ambiguous indication of stall and how deep it is, as opposed to guessing from a combination of airspeed, flap/slat settings, weight, attitude & wing loading.
The gold standard for software design in the aircraft industry is model-based design.
Everything comes back to the requirements document. The trouble is that the requirements document can never be perfect no matter how much quality control the system has. It is always possible to have a set of circumstances that the writers of the requirements document never thought of.
With very complex systems it is wise to start with a basic design that will fail safe. It is possible to design nuclear reactors that don't need active cooling. They don't rely on pumps to keep the reactor from mellting down. It is possible to design aircraft that don't stall. Burt Rutan demonstrated that with his canards.
Start with an inherently safe design, don't try to make the system safe with complicated systems that can never deal with all the possible contingencies.
From what I've read, the stall warning actually went away when the co-pilot pulled the nose up. I can't recall if that's because the pitot tubes were still messed up, or simply that the airspeed was too low that the stall warning only came back when speed was restored.
I read on pprune that this may have been avoided if there was angle of attack indication in the cockpit (plus training to use them). Apparently AoA is already measured by these aircraft, and such a reading would be much less ambiguous than guessing about how close to or how deep into a stall you are from airspeed, attitude, flap/slat settings, etc.
Now, I'm not an expert in the English language, but I can try:
It means that whenever one pilot pulls his stick (no pun intended), the other pilot won't sense anything in his stick. The other pilot will simply not be aware that the first pilot is doing some (possibly incorrect and fatal) action.
An alternative would be for the sticks to be linked, either mechanically (difficult) or electronically using servo motors (easy and common even in commercial products).
c++;
A mechanically linked stick set up, if the one pilot is pushing one way, and the co-pilot is pushing the other way, you'd feel the resistance and you'd know something is wrong.
On the Airbus however, if your pushing to the right, and your co-pilot decides to push to the right cause he sees your about to hit a tree, your co-pilot's stick is in neutral, so not only does the plane not accept his input, your stick doesn't attempt to move in the direction your co-pilot is pushing, so you have no idea your co-pilot is trying to move you away from that tree.
Correct me if I am wrong, but this has more to do with the commands than with the flight-by-wire per se. Boeing has in some planes flight-by-wire, but by design they retain the yokes (rather than joysticks) that work simultaneously. I think they retain it just for this reason. So if something is to blame is the way commands are designed in the "front-end". The "hardware "back-end" works just fine.
In a Boeing plane, the control columns (Big huge steering wheel like thing between each pilot's legs) are mechanically linked so when the pilot moves one, the other one moves as well.
In an Airbus plane, they have a joysticks next to each pilot on the outer side of the plane. When the first pilot moves his stick, the second pilot's stick doesn't move at all, it just stays centred. And because of the way the joysticks are positioned, the second pilot can't easily see what the first pilot is doing with the stick without a bit of effort.
...but lack of feedback in the second stick. I suppose this would be a relative easy addition, even to existing aircraft, if it is decided this would be a worthwhile safety measure.
Ponca City, We Love You
The joysticks are not linked. If one joystick is being pulled back, the other joystick does not move. So one pilot doesn't know what the other pilot is doing by looking at his own controls. He has to look at the other pilot's controls.
Well, there's spam egg sausage and spam, that's not got much spam in it.
It's complicated...
When one pilot takes over flying, whether mechanical, hydraulic, or electronic controls, a confirmation is supposed to happen -- something like "You have the plane" and an acknowledgement. This has been true for several decades. It doesn't make sense to blame fly by wire if the pilots the did not use the established protocol, and it is not even clear whether the pilots did.
No, that's not what happened at all. It's quite clear what happened. The one pilot was a fucking moron, and he had the stick pulled back the entire goddamn time they were stalled out and falling out of the sky. The other pilot had his stick pushed forward, trying to nose it down and gain some airspeed. The piece of shit computer system on the Airbus averaged the two inputs, finally concluding that keeping the control surfaces level was a good compromise. Only seconds before impact did the junior pilot (who should have never been behind the stick of a Cessna, let alone a commercial aircraft) release his control stick, allowing the aircraft to begin recovering, but by then it was too late.
This is more of a loss of instrument data problem. The pilots (and the computers) did not have reliable altitude, airspeed, or vertical speed information. They were in a storm at night. Read the third interim report, which has the data from the flight recorders. See section 1.16.6, "Reconstruction of information available to the crew".
Bear in mind that this event started with loss of airspeed information: "The PF then said âoeWe haven't got good ... We haven't got a good display ...of speed"
and the PNF "We've lost the speeds"." This was due to pitot tube icing. From the voice recorder information, it appears that the pilots never again trusted the airspeed information presented. The speed data did come back for a while, but then was lost again.
The aircraft was then in a high altitude stall: The airplane's parameters were then: altitude about 35,800 ft, vertical speed -9,100 ft/min, computed speed 100 kt and falling, pitch attitude 12 deg. and engine N1 for both engines at 102%. But one of the pilots said At 2 h 12 min 04, the PF said that he thought that they were in an overspeed situation, perhaps because a strong aerodynamic noise dominated in the cockpit. The report says "Despite several references to the altitude, which was falling, none of the three crew members seemed to be able to determine which information to rely on: for them, the pitch attitude, roll and thrust values could seem inconsistent with the vertical speed and altitude values."
Again, this is in a storm, at night, over ocean. All the crew has is its instruments. The crew misjudged which data was correct and which was wrong. Still, they had several minutes, three pilots, and plenty of airspace and altitude to deal with the problem. There was a way out. If the initial events had happened over high mountains, there would have been far less time to deal with the situation.
There are fighters which are designed unstable for maneuverability and can't fly at all if they lose their air data inputs. They have ejection seats. Transport aircraft are more stable and can manually flown without air data inputs, but it's not easy. A technical argument here is that aircraft with computer-assisted flight controls should have much more redundancy in the basic air data inputs (altitude and airspeed). If the sensors had worked, the computers would have prevented this. The Airbus had three pitot probes, but they were all the same, and vulnerable to icing. It may be appropriate to require some completely different sensors, mounted on different parts of the aircraft, as a backup.
Much of the blame belongs to Thales, which built the pitot probes. There were known problems with those probes before this crash. Air France has since replaced all Thales probes with Goodrich probes.
I find the half-assed approach when it comes to automation disconcerting. Either let the computers fly it and the humans are simply there as adjuncts and baby sitters, or let the humans fly it and the computer just corrects for fuck-ups. But in this case it was bunk information that confused even the computer. Blacking out screens is sort of a half-assed way to go about telling the world you're confused.
And why is it they still use Pitot tubes when GPS has fairly high resolution in three dimensions?
This post was apparently written for you.
Case in point, the source article is from Telegraph which is.....based in the UK.
Whoever he is, he always specializes in horror and suspense scenarios
...and it all boils down to pilot training and aircraft design philosophy differences between Europe and USA.
The "European" way is that the pilot resolves himself to simply be a subservient operator of the "system", that the "system" always knows better what's going on and how to proceed in any given situation. The USA way is that the pilot is always *PILOT IN COMMAND* and the first job is to *FLY THE AIRPLANE* no matter what the "system" is telling him or trying to do with the airplane, and if the "system" is fucking up, you do whatever is necessary to override the system to wrest control back to the pilot... and the pilot is trained to always be in touch with what the airplane is doing at all times.
The problem is the same as on the roads we see everyday. Morons "at the wheel" with absolutely no clue what they are really doing.
It seems quite clear that even some basic level of training beyond lift off, land, and go straight would have solved this issue. Namely, basic air aerobics training, even if just in a simulator. Being capable of handling whatever vehicle you are controlling at or near the extremes is a vital skill in near situations.
Not only does that give you tools to correct it, but it also makes things "go slower", ie. you are not panicking, you are more clear minded at these situations, and at the extremes, for a highly skilled individual, your brain knows when to "goto overdrive mode", the moment things seems to become slow motion and when moving your hand even a few inches seems to take a forever.
Also, a pilot should be able to "feel in his arse" the rough acceleration and yaw of the plane, these "sensors" are built into all of us. Never mind even in aircrafts a basic accelerometer and GPS should reveal the course of movement even if all other sensors fail.
If the junior pilot really kept pulling up, it's akin to a automatic car driver purely thinking "acceleration pedal is go, brake pedal is stop."
I mean, how stupid you got to be to think you can fix stall by pulling up? How numb do you have to be not to realize wanted action is not happening by the yaw and acceleration felt? I know i can feel even very minor differences in acceleration, but i guess for some people it ain't the same.
What did Chernobyl, Three Mile Island and the Space Shuttle Challenger have in common?
All three disasters were due to erroneous decisions made by (otherwise) smart, trained people at the wee hours of the morning. This has been shown to be have a bad effect on human decision making,
So the first thing I noticed was the fact that this disaster happened at 2am (not sure what time zone it was in or what time zone the pilots were in but you get the point).
Obviously someone has to be awake at all times to fly a plane (or operate a nuclear plant) but perhaps they could've timed the captain's rest better and made it clearer who was in charge when he was asleep.
The joysticks are not linked. If one joystick is being pulled back, the other joystick does not move. So one pilot doesn't know what the other pilot is doing by looking at his own controls. He has to look at the other pilot's controls.
True, but from what others have written here, you get an warning message "DUAL INPUT" yelled at you by the computer when both are trying to control the plane via the joystick, so it's not as if the pilots are not aware that the other one is also doing something. It seems that the pilot in this crash chose to ignore the warning that the copilot was also trying to control the plane for too long.
So yes - the Airbus system makes it impossible to feel what the other guy is doing when you hold the joystick, but you ARE aware that the other one IS doing something, too. And you can then tell him to let go of the joystick.
Some time ago I read a lot about the stupid Airbus stick control which "averages" the movements of both pilots and *does not* have force feedback.
How I saw it was that while the pilots *knew* the plane was stalling, they did not know *why*. That piece of information could have been obtained with a typical joystick system were both pilots' sticks are mechanically connected (coupled).
I even remember a study (in 1987) where pilots explicitly prefered coupled sticks :
In a 1987 evaluation of side stick controllers Summers et al (1987) found that under simulated ‘surprise’ hand overs pilots Cooper Harper rating of the schemes were (in descending order):
Coupled sides sticks with algebraically summed inputs (1.4),
Uncoupled side sticks with algebraically summed inputs and disconnect switch (final A320 implementation) (1.8),
Uncoupled with algebraically summed inputs and priority logic (original A320 implementation) (3.3), and
Uncoupled side sticks with with algebraically summed inputs (3.4).
Why did Airbus decided to use uncoupled sticks? that will always remain a mistery to me.
It's more than about fighting for control. The pilot at the controls was attempting to climb but the other pilot and the captain did not know this. The last part of the conversation had the 2nd co-pilot and the captain telling the pilot to climb to which he responded that the had been climbing the entire time. Realizing that was what was causing the stall, they then told him to descend but by that time, they didn't have enough altitude to get out of the stall.
Well, there's spam egg sausage and spam, that's not got much spam in it.
I've done a little researching on the A330's sensor system, and here is what I have found. Firstly, this article describes pilot union concerns about the official report, and details some interesting facts about the stall warning system. Specifically, the stall warning system on the A330 sounded for 50 consecutive seconds before ceasing. This was apparently due to the computer system automatically turning off the warning once the plane had dropped below 70 miles per hour, since that speed was supposed to be far outside the operating parameters of the plane. When the pilots finally pointed the nose down and gained airspeed, the stall warning began to sound again.
Here is another very interesting and authoritative article on the specifics of the A330 stall and angle of attack systems. The A330 does in fact use an angle of attack vane as pictured in the linked article. Interestingly, according to the article, the angle of attack is not actually displayed clearly or at all in the cockpit. This seems to me to be a gross design deficiency in the A330.
So, here is how I see it. The airspeed pitots were almost certainly frozen, causing the pilots and the computer to lose knowledge of the speed of the air over the aircraft. However, the angle of attack indicator was based on different system, a vane, which was likely not affected by ice. The stall warnings in the aircraft were likely based largely on the computers sensor inputs from the angle of attack indicators. Thus, the pilot should probably have known, based on the stall warnings that the airplane had a high angle of attack, which was resulting in a stall. They should probably have suspected their pitots were iced, and known that the stall system was based on different sensor inputs. However, the fact that the stall warnings stopped due to low airspeed, and the fact that the angle of attack reading was not easy or possible to see contributed to the pilots' mistaken control inputs. In other words, the pilots likely should have known better, but the design of the instrument display and warning system had significant flaws.
This and no other is the root from which a tyrant springs; when first he appears as a protector - Plato (423 to 327 BC)
It is a complex number derived from the airspeed, physical angle of the wing design, shape of the wing and the horizontal status.
Is it a complex number, or is the calcultion of AoA from the data complex?
The problem was more fundamental than the cockpit crew not being able to see what the pilot flying was doing. The problem was that it seems that nobody knew what were the right inputs to make. As the summary of the investigators interim report puts it:
- Neither of the pilots made any reference to the stall warning
- Neither of the pilots formally identified the stall situation
I think it's more than that. I think this is possibly what is referred to as cockpit resource management. The pilots were not communicating, which is the single worst thing that can happen in an emergency. The captain should know what the first officer is doing and vice versa. so when the stall warning came on, they pilots should have diagnosed the problem together, and agreed on the solution, and implemented it. In this case, nose down, and some throttle may have been the correct solution, but both pilots needed to know that this is what they needed to do.
I don't get. I recall the video of pilot's training flying a small plane. An instructor was repeatedly saying to the trainee the routine "check your speed, check your attitude", every 2 seconds. And here? What, nobody looked at the attitude indicator throughout the situation??? And the no doubt have ground speed indicator from GPS. Nose pitched up, no ground speed. And "stall" warnings. And they can't put those three together? I can't believe it....
Bonin thought he is in TOGA mode. What, he did not see the height indicator as well?
No, it's not American. But it is virulently anti-European.
add stick input vector to HUD
I run: Windows, OS X, Linux, FreeBSD. Just because you have a hammer, doesn't mean everything is a nail.
European pilots do not train for flying large aircraft in the same manner as US pilots. They use a system that I believe is called Ab Initio (From the beginning). Family connections plus some ability to pass tests gets you chosen to be a pilot. Then you start training in the actual airplane you will fly. These pilots have never flown small Cessna trainers and really don't have the practical understanding of how an airplane flies. Contrast that with the US system where a young pilot aiming for a professional position with an airline flies for thousands of hours as an instructor with idiot beginning pilots (to build his time). You really get to know what happens with a plane when you stall it hundreds of times, even enter some incipient spins now and then. The pilot that flew the ill-fated A330 into the rink probably had only been shown in the simulator a few times each year that the plane would not let you enter a stall, so he didn't recognize it when it occurred.
This is going to be a problem with US pilots also. In modern commercial flying, the autopilot flies the plane from shortly after takeoff till shortly before landing (or even after landings at Category III C ILS landing systems) and over a career will loose the "seat-of-the-pants" flying intuition they started with, leading to more accidents when they actually have to fly the damn plane manually.
The Telegraph likes to bash Europeans at every opportunity.
One thing that perplexed me - why did they not think about engaging auto pilot back again? or is that not possible once it shuts off ?
Tactile feedback for the inexperienced pilot may or may not be a factor. When I say inexperienced that could include a 20,000 hour plus pilot who has never experienced it. OTOH the "tactile feedback" in the control stick can be actual feedback from the control surfaces, simulated by the computer, or a pair of springs in the stick. The pilot can not tell the difference with one important exception. As you slow close to the stall the forces become less. In some planes the change in feedback Vs speed can be substantial. In others the changes may be at the very high and low ends and in some it's basically just at the very low end. Just before the stall it feels like the stick has been disconnected. Flying a plane with no feedback is an interesting experience. I had the opportunity to fly one that had no "break out force"and no stick gradient (increase in force the farther you get from neutral) and even though the stick was mechanically connected to the control surfaces there was no feedback. . It also had very sensitive and responsive controls.It was exactly like using a joystick in a game with no springs, but with "Gs"http://www.youtube.com/watch?v=4JkcrtvN60s was lost when the computers put it into a low speed PIO, or would that be CIO?