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Flight 447 'Black Box' Decoded 449

Posted by timothy
from the impressive-feats-come-in-waves dept.
fermion writes "An initial report has been released by the BEA concerning the details of the last minutes of Flight 447 en route from Rio de Janeiro to Paris. According the report, the autopilot disengaged and stall warning engaged at 2 hours 10 minutes and 5 seconds into the flight. Less than 2 minutes later the recorded speeds became invalid. At 2 hours 14 minutes and 28 seconds, the recording stopped. The final vertical speed was recorded around 10,912 ft/min."
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Flight 447 'Black Box' Decoded

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  • Umm, no... (Score:5, Insightful)

    by Maury Markowitz (452832) on Friday May 27, 2011 @07:04PM (#36268574) Homepage

    “So, we think that until impact they did not realize the situation, which for the family is what they want to hear — they did not suffer.”

    A three minute decent at 10,000 ft/min over the middle of the ocean?

    I'm pretty sure everyone onboard knew exactly how that was going to end about half way in.

    • by Hatta (162192)

      If it's free fall, it would be 3 minutes of weightlessness. The end would be quite abrupt.

      • Not quite free fall. My back of the envelope calcuations (38000 feet in 3 mins 30 secs) shows that assuming constant acceleration, the descent acceleration would have been approx .5 m/s^2 . This is about what you would experience in an elevator going down before the elevator reaches constant speed.

        • I doubt the acceleration was constant, furthermore it looks like they rolled the plane significantly, which definitely would have been noticed by the passengers.
        • It sounds like the plane was flown into the ocean. It was 12.7 km high at cruising altitude, so the rate of descent was 217 km/h. The cruising speed of an A330 is 871 km/h, so the pitch of the aircraft was roughly 14 degrees below the horizon.

          In heavy turbulence it might be very difficult to tell if accelerations up and down balance out over the course of a few minutes, allowing a nose attitude to go unnoticed. The downward acceleration may well have begun in the minutes leading up to the "3 and a half minu

          • by rthille (8526)

            The articles I read stated that the nose was up, not down, and that was the problem, the plane was stalled, nose-up, flying too slow and falling out of the sky.

            Then again, having read stuff I know something about in the media, I know not to believe anything I read in the media.

            • From my reading, it sounds like the stall warnings were not heeded due to the inputs mainly being nose-up, which is not how a stall is dealt with. The proper course would normally be nose down to regain speed and lift.

              There would have been less room for error as the stall began because the plain was near its operating ceiling which would be around 38k feet, and speculation is that the plane may have been in a deep stall, where the AOA is sufficient to wash out the rear stabilizers behind the wings.

              I think t

      • by Big Smirk (692056)

        Its not free fall. Once the plane descends at a steady rate, the passengers inside would feel normal gravity.

        Only if the plane continues to accelerate downwards would it continue to feel like free fall.

        Having been in a plane that was intentionally stalled, It is pretty much like a roller coaster. No one expects a roller coaster at 35,000ft.

    • Re: (Score:3, Funny)

      by jhoegl (638955)
      Saying "They did not realize the situation" is in fact true. They had no idea cheap speed sensors purchased by the plane manufacturer did not protect against freezing.
      • by Simon80 (874052)
        Citation needed.
    • Re:Umm, no... (Score:5, Interesting)

      by Bitsy Boffin (110334) on Friday May 27, 2011 @07:26PM (#36268750) Homepage

      1. Unless it's pressurization system was faulty (it wasn't) the pressure change wouldn't have been great.
      2. Unless accelerating, you wouldn't know you were going down (or up, or banked or upside down...).

      So the claim that the passengers probably didn't think it was anything more than turbulence is not hard to believe.

      It is perhaps surprising to non-pilots that you can be in unusual attitudes and not know it, pilots however are acutely aware. VFR (Visual Flight Rules) pilots flying into IMC (Instrument Meteorological Conditions - ie, zero visability) is a big cause of crashes, not because they can't see where they are going, but because they don't know which way is up.

      • To be clear, this was not a case of VFR into IMC, an airliner is basically IFR all the way these days.

      • by n1ywb (555767)
        Have you eve played flight simulator? There's this thing called an "artificial horizon" that tells you exactly how you are oriented. It is not affected by freezing of the pitot tube.
      • but because they don't know which way is up.

        This is why all the pilots I know tie a washer to a string and tape it to the cabin ceiling. No matter what an instrument says, that washer will point down.

        If you are buried in an avalanche you can use a similar trick to figure out what way the surface is, so you can dig yourself out.

        • Re:Umm, no... (Score:4, Informative)

          by rthille (8526) <web-slashdot@nOSpAM.rangat.org> on Friday May 27, 2011 @08:38PM (#36269366) Homepage Journal

          Um no. The washer will hang in the direction opposing the acceleration you are undergoing. If you are upside down in the plane, diving toward the ground at 2G's, it'll feel like one G toward the floor of the plane (up).

        • Re:Umm, no... (Score:5, Insightful)

          by jshackney (99735) on Friday May 27, 2011 @08:48PM (#36269476) Homepage

          I don't think you know any pilots because if you did, you'd know that this little trick doesn't work. [citation [youtube.com]] rthille is correct.

        • They do that to coordinate their turns (using the correct amount of rudder in addition to ailerons). The goal is to keep the string pointing towards the floor (not towards the earth) at all times. Even when in a 45 degree banked turn. And even when upside down during a barrel roll. The string does *not* point down.
      • 1. Unless it's pressurization system was faulty (it wasn't) the pressure change wouldn't have been great.
        2. Unless accelerating, you wouldn't know you were going down (or up, or banked or upside down...).

        So the claim that the passengers probably didn't think it was anything more than turbulence is not hard to believe.

        This pre-supposes that the passengers felt approximately 1G of gravity downward from their point of view, which pilots normally carefully maintain for passenger comfort. A banked turn that maintains 1G of gravity downward by carefully controlling the turn rate feels "normal" as if the plane were flying straight. Pilots can't do this in an emergency when there are systems failures.

        Remove that 1G of gravity like in a free-fall, or flying straight down, and the passengers are going to become acutely alarmed

    • by jambarama (784670)
      Just FYI, 10,000 ft/min is only about 113 miles per hour. [google.com] Typical cruising speed for a long-distance large jet aircraft is about 550 mph, so the pilots had slowed the plane quite a bit. The plane didn't go screaming into the ocean.
      • The forward velocity is not stated. We don't know "the pilots had slowed the plane quite a bit" What is stated is than the engines were running at near full thrust, the plane was 40 degrees nose up, and the plane was falling at 120 mph. This would appear to be a stall condition, and either the person at the controls lacked the skill to pull out of the stall (or didn't realize his predicament) or the airplane itself lacked the ability to recover from such as stall.
      • by Big Smirk (692056)

        Uhm, that's vertical speed. The problem is the plane slowed down to the point it couldn't maintain proper airflow over the wings. Thus the stall warning.... and well, the stall. Unexplained is why the pilots kept the nose of the plane up. I would imagine at some point that would cause a spin. The recovery procedure for a stall is full power and nose down until your airspeed comes up again.... your forward air speed.

        My only thoughts is that the pilots didn't believe the stick shaker since they were pret

    • by catchblue22 (1004569) on Friday May 27, 2011 @08:39PM (#36269376) Homepage

      I have been reading the report and there are some strange interesting passages. Here is a partial summary, focussing largely on pilot control inputs

      Copilot is PF. Captain is PNF.

      2 h 08 min 07: "...turbulence increased slightly and the crew decided to reduce the speed to about Mach 0.8"

      2 h 10 min 05: "...the PF made a left nose-up input. The stall warning sounded twice in a row...Autopilot and auto-thrust remained disengaged for the rest of the flight."

      2 h 10 min 16: "...The airplane’s angle of attack increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs... The airplane was then at an altitude of about 37,500 ft"

      At 2 h 10 min 51: "...The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs...The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight...The PF continued to make nose-up inputs."

      2 h 11 min 40: "...The airplane’s pitch attitude did not exceed 15 degrees and the engines’ N1’s were close to 100%..."

      At 2 h 12 min 02: "...At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55%. Around fifteen seconds later, the PF made pitch-down inputs..."

      This much seems clear: the airplane was cleared for flight level 350 (35000 ft), and was likely at that altitude when the trouble started, assuming the altimeter was functioning. Stall warnings went off, and the airplane climbed to 38000 ft. It then descended rapidly, it seems with a monstrously high angle of attack. It also seems from the report that the nose of the plane was mostly pitched up through this, though I am not absolutely sure on this. This would imply a very bad stall...essentially the airplane was falling from the sky. One can speculate that the pilots were doing their best to recover from the stall with imperfect data on their airspeed.

      To me the important period was between 2 h 08 min 07 and 2 h 10 min16. There was a decision to reduce speed, which would entail a reduction in thrust. Two minutes later, there was a stall warning, implying that the airplane's airspeed was out of the very narrow range required at that altitude (plus/minus 10 knots according to the Nova documentary, though I'm not sure it's so narrow). The question is, what caused those initial stall warnings? How did the airplane's speed get out of the proper range? Did the pilots forget to increase thrust after the autopilot reduced it? During those two minutes, was the airplane catastrophically slowing down?

  • So far, there is no speculation as to why the airspeed sensors failed or assignment of blame. It is noted that the co-pilots tried to take control and may have stalled the plane. Nothing in the readings contradicts the leading theory of icing on the pitot tubes. It may take a year for a full report.
    • Yeah, can't fault the NTSC's way of doing this... refuse comment until you're sure you have something to report.

      • by OverlordQ (264228)

        NTSC?

        That's a video system. Do you mean the NTSB? They're not really involved either, it's the BEA [wikipedia.org].

    • by spongman (182339)

      i believe the speculation is that the heaters in the sensors were faulty/insufficient and they became clogged with ice. the flight envelope at high altitudes is very narrow and apparently very difficult to fly without reliably knowing the airspeed.

      • "...apparently very difficult to fly without reliably knowing the airspeed."

        That is true on any situation, any altitude.

        • True, losing airspeed indication makes the situation very difficult, but not impossible to handle. As long as you know altitude, attitude and throttle setting, as well as the resulting climb/sink rate for a certain trim, you can still work it out. In the middle of a thunderstorm out of hell, at night, with hell breaking loose all around you, well... yeah, then all bets are off. But generally speaking, you can handle a plane without airspeed indication, and that is trained for.
          • The training has proven to be entirely inadequate. This type of accident is far too common, since the earliest days. One guy should always be flying the plane, but all too often everybody's trying to troubleshoot the problem. and even in a storm it is possible to maintain control with a working artificial horizon and a fixed power setting as you point out.. Key word is 'situational awareness'. Lose that, then indeed, all bets are off. A lot more hours in the simulator are needed to burn this into the guy's

        • i would guess not. air closer to the ground is denser, supplying more lift ? hence "the flight envelope at high altitude is narrow" ?

        • "...apparently very difficult to fly without reliably knowing the airspeed."

          That is true on any situation, any altitude.

          Flying by the seat of their pants, most instrument qualified pilots should be able to guess airspeed well enough to stay flying below about 20K feet. Stall buffet indicates you are too slow. Screaming airflow: too fast. In the middle, just right.

      • by bob8766 (1075053)
        The pilots have to keep the plane within a pretty strict speed range to both keep the plane together and avoid a stall. Even when the speed sensors fail and the pilots have no airspeed indicator, there is a standard procedure that allows them to keep the plane within that narrow range by setting the throttle and controls at specific settings until it unfreezes. Frontline even aired a special where two flight instructors demonstrated this after being presented with this exact scenario in a simulator. The
    • Yeah, can't see any causality there so far. The speeds given in the press releases I read only show that there was a stall. If this happened due to faulty speed readings, pilot error - maybe due to loss of orientation in a very confused environment -, or the pilot fighting an actually correct behavior of the plane is completely open so far.
    • by fluffy99 (870997)

      The answer is pretty much in the report. The co-pilot put full thottle on and kept pulling up, probably not understanding that that they were losing altitude because they were in a stall situation.

      • The assignment of blame is not in the report yet as this is initial. While it is curious that the pilot pulled up, one expert noted that after the stall, the plane should have lowered the nose which would have aided in stall recovery. The nose however stayed up which might mean that the rudder was frozen by ice or immobile by other factors. That would turn the stall from a simple stall to a "flat stall" which is unrecoverable. If there was ice then the pilot may have initially pulled up but could not pu
        • Actually, this makes the most sense of all I heard so far. Since - as I had to learn by painful correction to my mistaken initial assumptions - the stall warning went off, but the system still recorded the PF maintaining and even forcing a nose up attitude, loss of control surface movement seems somewhat probable. The throttle went to TO/GA, so they definitely tried stall recovery - which makes it quite improbable that they would have willingly forced nose up. Unless they were seriously mistaken about altit
      • I'm not a pilot, but shouldn't increasing the throttle help recovering from a stall?

        • Increasing throttle is half of it - and they did that. To quickly regain speed, you push the nose down, too. That did not happen. And that is actually interesting. Either they could not do it because they lost attitude control at this point, or they thought they could not do it, because they thought they had no altitude to sacrifice for speed.
        • by michelcolman (1208008) on Saturday May 28, 2011 @09:00AM (#36272680)
          No, because in most jets extra thrust will actually push the nose up since the engines are located under the wing. The most recent procedures actually have you reduce thrust to bring the nose down more quickly.
      • The answer is pretty much in the report. The co-pilot put full thottle on and kept pulling up, probably not understanding that that they were losing altitude because they were in a stall situation.

        Anybody who has spun a sailplane would know to put the nose down in that situation. Maybe these guys had never done that.

    • If it was the initial stall they must have really stuffed up. If you can get the aircraft flying at 20000 feet, you won't have to be anywhere near stall speed and you can fly manually as long as you want. Airliners are not jet fighters. Stall recovery should be straightforward, at least once you have lost some altitude. My uncle, when he was a flying instructor, said he would take a VFR qualified pilot into cloud and they would inevitably exit the cloud in a spiral dive, but airline pilots should be able to

  • by spongman (182339) on Friday May 27, 2011 @07:09PM (#36268614)

    = 124 miles/hour

  • by Kenneth Stephen (1950) on Friday May 27, 2011 @07:11PM (#36268630) Journal

    What seems to be remarkable is that the trigger to the catastrophe has indeed been revealed to be the pitot tubes - something that was suspected very soon after the flight went down. To a layman like me, it is amazing that without the benefit of all the data that has been recovered from the flight data recorders, experts were able to get so close to the mark.

    Now, one could flip this around and also say that given that so many observers were able to so accurately get to the initial trigger for the failure in the absence of hard data, it must mean that this was a really common failure mechanism that should occurred in the field only as a result of the problem being repeatedly ignored.

    It is a triumph of technology that the flight data recorder survived under such extreme conditions for so long. It was a triumph of technology, that it was located and retrieved from such an extreme location. Surely, a species with such (magical?) technical expertise could have expended the effort into preventing such a failure?

    • by hawguy (1600213)

      What seems to be remarkable is that the trigger to the catastrophe has indeed been revealed to be the pitot tubes - something that was suspected very soon after the flight went down. To a layman like me, it is amazing that without the benefit of all the data that has been recovered from the flight data recorders, experts were able to get so close to the mark.

      Now, one could flip this around and also say that given that so many observers were able to so accurately get to the initial trigger for the failure in the absence of hard data, it must mean that this was a really common failure mechanism that should occurred in the field only as a result of the problem being repeatedly ignored.

      Since the pitot tubes were known to have problems before the crash and Airbus had recommended (but not required) their replacement prior to the crash, perhaps it's not so remarkable.

      • Airbus couldn't require anything from anyone, but several countries did require their replacement before the accident. Unfortunately, France wasn't one of them.

    • by Anonymous Coward on Friday May 27, 2011 @07:40PM (#36268868)

      To a layman like me, it is amazing that without the benefit of all the data that has been recovered from the flight data recorders, experts were able to get so close to the mark.

      Airbus records remotely some telemetry data, this is how experts where able to make a sensible guess.

      Surely, a species with such (magical?) technical expertise could have expended the effort into preventing such a failure?

      Yes, of course. This will be taken in account in future projects and into airplane maintenance routines. But ya know, those damn birds are already very reliable. It's a disaster, my heart will be always with the families. But some times, you know, shit happens. We should always be aware of how fragile the human condition is and understand that despise all of our hard work into making things safe, some times the unexpected happens and a disaster awaits our destiny.

      Yours sincerely,
      Someone who deals with safety systems (not at Airbus ) and it's tired to see people blaming designers: we did our best.

    • To a layman like me, it is amazing that without the benefit of all the data that has been recovered from the flight data recorders, experts were able to get so close to the mark.

      That's a logical fallacy. If enough experts (and not-so-experts) predict enough different reasons for the flight failure, then when the real reason is discovered, some expert will be very close to the mark. You're filtering out the prior speculation and choosing the segment that happened to agree with posterior conclusions. It

      • With respect to your comment that this is a logical fallacy - its not so. The pitot tubes have been for the past two years the #1 reason put forward as the cause - by a wide margin. There have been no alternative theories so widely championed. Go back through the news articles and see for yourself. If you find that too difficult, you can use the wikipedia page on this disaster (look at the page history).

        And if one did flip this around, one would be wrong. The characteristic of a common failure mechanism is that it is common. As such, it gets addressed by virtue of its repeated occurrence during repeated tests. If it does not occur frequently, then it simply isn't common.

        I don't understand what you are trying to say here. You seem to be conceding that this was a commonly occ

    • by OverlordQ (264228) on Friday May 27, 2011 @08:01PM (#36269058) Journal

      Surely, a species with such (magical?) technical expertise could have expended the effort into preventing such a failure?

      There is, it's called heated pitot tubes, and the FAA requires them for US carriers.

    • by bragr (1612015) *

      To a layman like me, it is amazing that without the benefit of all the data that has been recovered from the flight data recorders, experts were able to get so close to the mark.

      If you recall, we did have the diagnostic messages that they airplane was sending back home, which, if I recall correctly, helped identify the cause the problem. The idea of the tubes freezing up was not a shot in the dark.

  • Then he wouldn't have put corrupt manufacturers and regulatory agencies in charge of the airplanes.

    I've logged plenty of airmiles, but I'm never climbing aboard one of those hand grenades again in my life.

  • So far, the NOVA summary [pbs.org] is on target. In addition to the pitot tubes freezing, which is an obvious design flaw, it sounds like the pilots reacted improperly to the loss of speed data.

  • It's randomly on a car forum, but its worth a read. Some guys that know what they're talking about talk about what they think happened. They also include pics of various airbus cockpits for reference.

    http://www.mye28.com/viewtopic.php?t=64381&postdays=0&postorder=asc&start=25 [mye28.com]

    Here's the basic story, as I understand it:

    - the pilots flew into a thunderstorm
    - they were 100% blind, relying entirely on the glass-screen instruments
    - once all 3 pitots froze, the redundant computers started disagreeing and then finally agreed that things were ugly

    the effect in the cockpit is that a serious of cascading failures were unfolding, likely overwhelming the pilots.

    additionally, there would be NO functional indicators for alt, speed, horizon, etc. Once the computers have faulted, they no longer share that information.

    Also, as the computers degrade authority, in an Airbus the pilots get MORE control of the aircraft. This means that controls move through larger ranges.

    As flight control reverts to failsafe mode, the controls in the cockpit do not "auto-zero". And the forcefeedback goes off line.

    Effectively, the pilots are 100% blind, and the inputs they make have no feedback whatsoever. They cannot even tell if they have _stopped trying_ to turn.

    Imagine being blindfolded. Your job is to put the end of a 4 ft long stick inside of a 1" circular hole in the floor. Except the stick is a peice of yarn.

    That's what their instruments and control apparatus were like.

    Now imagine that everything is beeping at you and you are in a plane in a thunderstorm, over the ocean, at night, and everything outside is total blackness.

    You're fucked. Thoroughly and completely fucked.

    • Re: (Score:3, Interesting)

      by superdana (1211758)
      I find it highly unlikely that clogged pitot tubes would take out all the static and gyroscopic instrumentation too. That would be a phenomenally stupid design, and would rank the Airbus lower than a Cessna 150 in terms of instrument reliability.

      The information in the report is preliminary, and there has to be more to this story. Even the lowliest weekend warrior pilot earning the most basic instrument certification has to demonstrate an ability to fly in IMC with multiple instrument failures.

      What I wan
    • If Air France's A330-300 are set up the same as SAS' (430KB PDF [www.sas.se]), there should have been a cluster of mechanical backups just to the right of the pilot's primary glass displays, including an artificial horizon. Even if the backup sink rate, airspeed indicator, and altimeter were returning bogus values, the gyroscope and compass wouldn't, and ergo there would have been at least enough information to know which way the bird was pointing.

    • by Carewolf (581105) on Saturday May 28, 2011 @06:23AM (#36272064) Homepage

      additionally, there would be NO functional indicators for alt, speed, horizon, etc. Once the computers have faulted, they no longer share that information.

      Alt. must have worked it is recorded correctly by the black box, I see no reason to believe horizon shouldn't have been working, so only visual and speed was impaired. That is still a difficult situation, so no reason to exaggerate it.

      • by bmajik (96670)

        My information suggests that the sensors feeding the black box either cannot or were not made available to the primary flight instrument computers, astonishingly enough.

        Given the amount of system isolation in aircraft this isn't entirely impossible to beleive. If you tie part B into part A's wiring in any way, you have to do more testing/verification than you would otherwise.

  • by Animats (122034) on Saturday May 28, 2011 @12:08AM (#36270678) Homepage

    The actual BEA report [bea.aero], which should be read before commenting, does not assign blame. That will come later.

    At one point, the left side airspeed display showed 215 knots, far above stall speed. The backup airspeed indicator showed 185 knots, also above stalling speed. The right side airspeed display value isn't logged. Then all speeds showed as invalid. Given that conflicting information, at night in a thunderstorm over water with no outside visual cues, it's not totally unreasonable that the pilots, finding themselves losing altitude but thinking they had more airspeed than they did, tried to pull up.

  • Margin of error (Score:5, Interesting)

    by slyborg (524607) on Saturday May 28, 2011 @12:56AM (#36270924)

    It seems very scary that on an aircraft with everything working but the airspeed indicators (and I understand that those are very important), after more than 3 1/2 minutes the aircrew was unable to prevent the plane from hitting the ocean. This was a state of the art aircraft. Makes you wonder how many close calls there have been that luckily didn't result in catastrophe.

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