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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.'"
This topic has been beaten to death by professional pilots and aviation experts on pprune.
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!
FYI they belly-flopped the plane, the nose was actually pointing up the whole time they were falling.
Are you under the impression that The Telegraph is an American publication?
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.
Yeah! Let's go smash up some looms!
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.
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.
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.
Every component in the system introduces the possibility of error, agreed.
People can detect and correct certain classes of error better than machines, but machines can detect and correct certain classes of error better than people.
People can self-repair, to an extent. Blake's 7 Liberator-style auto-repair is still sci-fi. Sadly.
Well-trained humans can identify errors in their training but can also forget the training that is correct. Computers cannot (yet) do either.
A perfect balance is what we need.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
First, I fail to see the relationship between joysticks and tactile feedback, secondly it's very possible and often done for fly by wire systems to provide force feedback and other haptic ques. The failure is with the designers of the system who opted to omit such feedback, not intrinsic to fly by wire.