Fly-By-Wire Contributed To Air France 447 Disaster 319
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.'"
More to it than that (Score:5, Informative)
This topic has been beaten to death by professional pilots and aviation experts on pprune.
yes, fly by wire downed the plane... (Score:5, Informative)
Re:More to it than that (Score:5, Informative)
and airliners.net also. The ones who know what they are talking about are unanimous in that it had little to do with the non-backdriven controls; the pilots flying were so disoriented that it probably would have taken a giant flashing sign saying "you're falling out of the air, dummies!" to get them to nose down.
And anyway, FBW != back-driven controls. The thread title is wrong and misleading. Boeing uses FBW too, but they back-drive the yoke and throttles. This has been discussed plenty as well, and there's no inherent advantage to one way over the other.
Re:More to it than that (Score:5, Informative)
But there is another, worrying implication that the Telegraph can disclose for the first time: that 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. And 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.
For the first time ? As you said, this has been beaten to death in various reports. There has already been an almost full transcript of the cockpit voice recorder leaked in a book [amazon.fr] months before. The last and final report from the investigators is scheduled to come out in June. They have put in place a special panel composed of pilots to try to understand the reactions of the crew (including seemingly ignoring the stall warnings, the apparent lack of confidence in the instruments, etc), and have dug into the history of flights during which pitots tube froze at high altitude. I think their conclusions might be slightly more revealing than the Telegraph copying-and-pasting other websites [popularmechanics.com].
Re:Feedback is important (Score:5, Informative)
FYI they belly-flopped the plane, the nose was actually pointing up the whole time they were falling.
Re:More to it than that (Score:5, Informative)
the pilots flying were so disoriented that it probably would have taken a giant flashing sign saying "you're falling out of the air, dummies!" to get them to nose down.
There was a recorded voice yelling STALL, STALL, STALL over and over again. They would have ignored the giant flashing sign too and blamed it on a computer error.
They were just that disorientated.
Re:Fly by wire.... (Score:4, Informative)
Unaware of the real arguments, i would say: complexity. It would make a critical component more prone to problems.
Please be aware: The control stick in an Airbus is a small joystick today which is not in the "line of sight" of both pilots. You would have to look at it directly or put your hand there to notice it's position:
http://pnaconsult.com/yahoo_site_admin/assets/images/2.293181416.jpg [pnaconsult.com]
In Boeing 787 the stick is much bigger:
https://upload.wikimedia.org/wikipedia/commons/thumb/8/8a/787-flight-deck.jpg/800px-787-flight-deck.jpg [wikimedia.org]
Linking them makes more sense than in an Airbus.
I have talked to some pilots and they prefer the Airbus way, but i consider them biased in favour of Airbus.
Re:Fly by wire.... (Score:5, Informative)
the thing with the Airbus control system is that you issue 'change' commands to the plane. you issue a 'roll command' when you push the stick to the side, and you issue a 'G command' when you push it forward or back. the plane will remain in the new commanded state until commanded otherwise.
(now read the last sentence again, and chew on it, make sure you understand it thoroughly)
thus, the usual way to fly the plane is to issue small, well-intentioned commands, not to pull on a stick for minutes, as one of the pilots here did. and the plane will stay in the new situation. 'will stay' means that it will issue corrections on its own to maintain the commanded attitude. for example, after having been issued a roll command for a few degrees, the plane will stay in that attitude even of there are disturbing factors - say, turbulence. (as a result, in such a case it is an error for a pilot to try to manually compensate for turbulence-induced attitude changes, as the plane does it on its own anyway, and he will end up over-compensating)
all-in-all, this is a big change in the philosophy on how to fly a plane, even when flying alone, when compared to a 'legacy' system of direct physical coupling of control instruments to control surfaces.
as for simultaneous inputs: actually, one of the pilots can 'take over' command of the plane, and shut out the other one, if he so chooses. none of the pilots did this on this occasion. when having multiple inputs, the plane does signal that the other person is entering inputs as well (at least visually, maybe there is also an aural indication). although, as pointed out, there is no physical feedback on the stick that would signal the other pilots inputs. when both are entering commands, their commands are 'added together'. thus a full pull & a full push on the stick will cancel each other out. two 'small' pushes will results a 'big' push. this makes sense, so that either pilot can 'adjust' the planes behaviour in addition to what is already happening.
the point of not having physical feedback is to reduce strain on the pilots. this way, the stick is always centered, and when moving off center, the pilot knows he's issuing commands to the plane. if it was not so, the pilot wouldn't be sure in which state of the stick is it in a 'neutral' position.
I hope the above gives some background to the story.
Re:More to it than that (Score:0, Informative)
Yes, but it's important that the Americans bash Airbus at every possibly opportunity, lest their own sacred calf not be fattened.
"The Daily Telegraph is a daily morning broadsheet conservative-leaning newspaper distributed throughout the United Kingdom and internationally. The newspaper was founded by Arthur B. Sleigh in June 1855 as the Daily Telegraph and Courier, and since 2004 is owned by David and Frederick Barclay."
In other words, Go Fuck Yourself.
Re:Fly by wire.... (Score:3, Informative)
while the co-pilots behaviour of pulling on the stick for minutes, and not recognizing the very simple stall-recovery process of pushing & gaining speed is, well, astonishing - there is a reason for his behaviour.
the reason is that such planes usually encounter stall-warnings on approach, when in a landing configuration, close to ground, and having a lot of excess power. in such occasions, the usual procedure is not to lower the nose & convert altitude to speed, but to simply 'power yourself out' of the stall situation - apply a lot of (available excess) power, and your speed will pick up, and you're not close to stalling anymore.
the fact that the co-pilot in question referred to TOGA (the Take-Off-Go-Around procedure) in the transcript, and the fact that they were using maximum thrust for most of the falling time also suggest that his idea of stall recovery was to power himself out of the stall.
this is quite unfortunate indeed, as any small-plane pilots instinct would have been simply to dip the plane's nose & recover easily.
Re:Fly by wire.... (Score:5, Informative)
Only the pilot in command should have his hand on the stick; so linking the two together wouldn't have any of the problems you raise. It would, though, give valuable visual (and tactile if both pilots are trying to control the stick) information to the co-pilot.
this is not how multi-crew cockpits (MCC) work - in these cases, both pilots have control. as said earlier, they can agree on only one of them giving direct inputs though.
this is all covered by CRM - Crew Resource Management - where the two pilots divide the tasks & responsibilities between them. both being young pilots (remember, the captain was sleeping at the time), they pretty much failed in applying proper CRM techniques. both were used to being the junior member of a multi-crew cockpit, thus neither of them took the initiative. this is quite evident from the transcript.
There is one reason and one reason alone Airbus didn't link the sticks - and that's cost (both in higher building costs and extra weight).
this is simply not true - adding feedback is neither expensive nor heavy in this case.
Re:More to it than that (Score:5, Informative)
Not only that, but the computer turned off the STALL warning when its sensors determined that it was going 60 knots in flight and decided it was wrong. It didn't tell the crew that it was shutting down the STALL warning due to sensor failure; it just stopped talking. When the co-pilot finally realized his mistake and began to nose down, the STALL warning turned back on again because the airplane had picked up speed. The co-pilot heard the STALL warning, freaked out, and began to pull up on the stick again. If he had kept nose down, the STALL warning would have gone away once the aircraft had sped up enough to get lift. It's a bizarre system all around.
Re:Fly by wire.... (Score:4, Informative)
There is one reason and one reason alone Airbus didn't link the sticks - and that's cost (both in higher building costs and extra weight).
>
The Airbus, like Boeings, have "Stick Shakers" to give feedback to the pilot. The stall waring indicator, in fact, does trigger the stick shaker, but once you get below a certain speed (like these pilots did) the aircraft thinks the plane is too slow to be flying so it must be taxing, so it turns it off.
Bill
Re:Fly by wire.... (Score:5, Informative)
On an A320, the audio signal is to have the in-cockpit speakers bawl 'DUAL INPUT, DUAL INPUT' at you incessantly. It's not some small ding you can't hear.
Re:More to it than that (Score:5, Informative)
No, they were never taught that Airbus aircraft will prevent a stall, no airline teaches that - what they did was assume the stall warning was incorrect, because they did not do their memory check lists as required by Airbus and Air France.
Re:Stall warning wasn't there, they needed AoA (Score:4, Informative)
The airspeed dropped to a level where it was ambiguous (below something like 60 knots indicated), and that killed the stall warning. It reactivated when they pushed the nose down, which increased the airspeed to above the threshold.
Re:More to it than that (Score:3, Informative)
I take it don't you don't live in England where English is spoken natively.
Wait for the full report (Score:5, Informative)
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 [bea.aero], 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.
Re:More to it than that (Score:3, Informative)
I am a pilot, and it is pretty obvious that the issue was that both of the young pilots just got behind the airplane. Just for the record, there is never a condition that a Stall horn should be ignored... These systems are always independent for good reason. The trainer aircrafts use a completely mechanical horn, and students must demonstrate several stalls to an FAA examiner (power on / power off) to obtain even a basic license. Meaning, there is no excuse for an airplane to stall other than pilot error.
Also, just because a pilot tube is stopped up, this is not a justification for not being able to manage the airplane. A simple cross scan with the other systems (Vacuum, Electrical, and especially GPS) would have told them that that static system was blocked. Icing is a very common occurrence to anyone who has a fair amount of IFR experience. Meaning, their pitot heater on should have been on the moment they knew precipitation was in the area. Even more, on any airplane once the leading edge accumulates significant ice, the airplane starts to feel an entirely airplane. Some airplanes even start to give a weird "howling" like noise that any experienced pilot can easily detect.
In short, the true reason for the crash is the classic pilot ostrich maneuver. Both of the young pilots decided to put their head in the sand hoping the problem would resolve itself rather than actually managing the airplane. The captain clearly understood this once he became involved, and was several minutes too late...
Time of (night) (Score:4, Informative)
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.
Re:Why all this speculation? The report was clear. (Score:4, Informative)
You are referring to "positive stability", which is absolutely designed into the non fly-by-wire aircraft, such as the smaller Cessna's, Piper's, etc. With a fly-by-wire aircraft, the computers can handle the stability by making fine adjustments, leading the designers to make the aircraft closer to neutral stability. More the positively stable an aircraft is, the more aggressively it returns to a normal flight level, but you lose maneuverability. Commercial jets being closer to neutral stability, gives them more maneuverability, and slightly better fuel consumption.
Have you heard the claim that modern air force jets need X number of computers to stay in the air? This is due to them being designed with negative stability, meaning any pilot induced oscillation will grow larger and larger, therefor the computers are required to compensate for the lack of aerodynamic positive stability. The negative stability gives them a massive amount of maneuverability.
Re:Why all this speculation? The report was clear. (Score:4, Informative)
In any fly-by-wire aircraft, the computers will return the aircraft to a normal flight attitude. So the A330 has reduced aerodynamic postive stability (still above neutral), but the computer involvement makes up for this. Of course, when you lose the pitots, the computers drop from normal law to alternate law, which means they stop intervening in some situations, and instead warn the pilots. The prime example is a stall - you can't stall an A330 when running in normal law, as the computers will manipulate the control surfaces to prevent this. In alternate law, the computers are unsure of the full picture, due to failed inputs, so they warn the pilots of a stall. In this case, you have lost some of the stability introduced by the computers - there is some stability there, but when you are pulling back on the side stick while stalling in a storm, no amount of positive stability is going to correct it.
Positive stability doesn't fix all situations. If you have too low a power setting, out of trim, CG not correct or even strong external forces (such as a storm), the a positively stable aircraft can fail to stabilise itself.
Think of your car steering wheel. When you turn, it takes effort to move away from straight, and you feel continued pressure to return to straight. If you let go of the wheel, it will return to a straight position. This is positive stability. If your car had neutral stability, it would take much less effort (ie no resistance) to move away from the straight position, and if you let go of the wheel, it would stay in the turned position you left it in. If you had negative stability, turning the wheel would induce a force in the direction of your turn, encouraging and pulling the wheel further into the direction of turn. Letting go of the wheel would cause a turn to full lock. As you can imagine, this negative stability provides much more maneuverability, but requires computes to be able to bring the wheel back to central when the pilot indicates as such through the control column.
Re:over use of tech (Score:4, Informative)
Yeah, I get the joke, so don't bother with whooshing.
The thing that always amuses (yet frustrates) me is that the Luddites weren't against technology, they were against workers being replaced by machines. If the mills had kept the same workforce but doubled production, diversified, or whatever, they wouldn't have complained.
A true Luddite would not complain about fly-by-wire as it's not replacing anyone. They'd applaud it because it was enhancing the skills of the people who were there.
Re:More to it than that (Score:5, Informative)
No, you're incorrect. There are various modes that the Airbus flight system uses. Under normal law, the airplane will not stall no matter what you do. You can pull up on the stick all you want, and the airplane will eventually gun the engines to avoid a stall. However, if the sensors are conflicting, the flight control software degrades into alternate law, which can be stalled. The flight crew might not have understood immediately that the alternative law mode had been engaged, and that a stall was probable. The entire episode took place in eight minutes with the captain being away, leaving two subordinates in charge.
Re:Why all this speculation? The report was clear. (Score:2, Informative)
Re:over use of tech (Score:4, Informative)
...which are fly by wire.