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.'"
Nonsense - Boeing fan at the wheel? (Score:2, Interesting)
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.
Just check what the guy's doing (Score:3, Interesting)
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.
Re:More to it than that (Score:5, Interesting)
Yes and no –the reason they were ignoring the voice saying STALL, STALL, STALL was because they believed that the computer software made it impossible to stall the aircraft, and that all the warning meant was "if you turn off all the computer assistance now, it'll stall", not "the computer assistance is already all off, I am stalling".
A second warning that doesn't ever sound in safe scenarios (e.g. FALLING, FALLING, FALLING) might just have made them twig to "crap, it really is stalling".
Re:The speed sensors froze up (Score:4, Interesting)
yes, this was how the whole thing started - that they got an incorrect airspeed indication, and thus the autopilot disengaged. after a short while, the speed indication was correct again. unfortunately, human errors added up starting from there.
although I would argue that the first mistake that they made was to fly into the storm, which every one else navigated around at that time. in aviation, you have to have at least 3 mistakes in a row to have an accident - here, flying into the storm, the frozen airspace indicator and then human error.
Re:Fly by wire.... (Score:4, Interesting)
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.
I'm not sure where you got that information, but that is not the correct course of action. Even in a low altitude situation, a stall can only be recovered by lowering the angle of attack... engine power and speed have absolutely nothing to do with it. A stall is an aerodynamic condition where the wings are not producing enough lift for flight. Pushing the nose over (to lower the angle of attack) allows the air to reattach to the wings which eliminates the stall condition.
Bill
Re:Fly by wire.... (Score:4, Interesting)
Issuing "small, well intentioned commands" is how it usually works, but in this case the flight controls had been switched into their alternate control law, due to the loss of reliable airspeed data. In alternate law the columns do what a "dumb" FBW system does, and stick displacement will reflect in contro surface deflection.
Why all this speculation? The report was clear. (Score:3, Interesting)
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.
Re:More to it than that (Score:4, Interesting)
The stupidest thing was, the whole thing was avoidable. The reason they stalled out to begin with is the junior pilot decided to begin a long climb, for absolutely no reason, losing airspeed all the while. Then they got into the storm and couldn't see anything, as the aircraft began to stall. Junior pulled back on the stick and kept it pulled back hard until 5-10 seconds before impact.
They fell out of the sky for minutes on end while the other pilot had his stick pushed forward, desperately trying to nose it down and gain some airspeed, perplexed as to what the hell was going on and why the damn thing wouldn't respond.....as the computer system averaged the two inputs, giving a neutral control surface orientation. (What kind of fucking moron designs an aircraft control system like this?)
A few times Junior let up on his stick and the aircraft corrected enough for the stall warning to begin buzzing, then in terror he yanked it back again. Only at the very end did he finally let up and the aircraft began to recover, just as they belly flopped onto the ocean at 90 MPH.
Why do it half assed? (Score:3, Interesting)
And why is it they still use Pitot tubes when GPS has fairly high resolution in three dimensions?
Re:More to it than that (Score:4, Interesting)
I haven't listened to the transcript, but there's a procedure for taking over controls. Was there ever a "my plane" or "my controls" yell from the captain to the fo? Did the capt confirm that the other pilot had his hand off the stick? I mean, damnit, if you're experienced and shit goes wrong, you must presume that the other people are fucking up until you confirm for yourself that they aren't.
Exactly (Score:2, Interesting)
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) [wordpress.com] 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.
Stall Warning Systems in the A330 (Score:3, Interesting)
I've done a little researching on the A330's sensor system, and here is what I have found. Firstly, this article [wsj.com] 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 [aviationad...ser.com.au] 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.
Re:over use of tech (Score:2, Interesting)
Ever think we're relying a little too much on technology these days?
The more bells and whistles, the easier it is to gum up the plumbing.
Same applies on cars, I've worked on one that would have a drive stall. Yeah figure that one out, the problem was the transmission computer causing feedback problems. Far worse on my 2012 car, where the radio, hud, and navigation system are all-in-one. Oh did I mention that the heater controls are also tied in? Yeah the hud died, took everything with a dash of electronics out too.
Now think about driving that sucker to the dealership when it's -35C, wasn't fun. And then I waited nearly 4 weeks for a new console to replace the broken one.
Re:Why all this speculation? The report was clear. (Score:4, Interesting)
If the pilots inputs are fighting each other like that then the aircraft screams "DUAL INPUT!" at them.