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Transportation Input Devices

737 'Tailstrike' Caused By Typo On a Tablet (arstechnica.com) 366

An anonymous reader writes: In August of last year, a Boeing 737 operated by Qantas experienced a tailstrike while taking off — the thrust wasn't great enough for the tail to clear the runway, so it clipped the ground. The investigation into the incident (PDF) has finally been completed, and it found the cause of the accident: the co-pilot accidentally entered the wrong plane weight data into the iPad used to make calculations about the takeoff thrust. "First, when working out the plane's takeoff weight on a notepad, the captain forgot to carry the "1," resulting in an erroneous weight of 66,400kg rather than 76,400kg. Second, the co-pilot made a "transposition error" when carrying out the same calculation on the Qantas on-board performance tool (OPT)—an iPad app for calculating takeoff speed, amongst other things. "Transposition error" is an investigatory euphemism for "he accidentally hit 6 on the keyboard rather than 7." This caused the problem: "For a weight of 76,400kg and temperature of 35C, the engine thrust should've been set at 93.1 percent with a takeoff speed of 157 knots; instead, due to the errors, the thrust was set to 88.4 percent and takeoff speed was 146 knots."
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737 'Tailstrike' Caused By Typo On a Tablet

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  • In the future, any flight engineer or pilot using that iPad to enter the plane weight data runs the risk of having it auto-corrected to the wrong value used by the crew in this case.

    No, not really. I hope.

    • by Austerity Empowers ( 669817 ) on Monday November 16, 2015 @02:27PM (#50941693)

      That'll make for some angry birds.

    • by sycodon ( 149926 ) on Monday November 16, 2015 @03:33PM (#50942269)

      Umm...Tail Strikes on take off are caused by over rotation.

      Regardless, seems to me that pilots calculating the take off weight is anachronistic. Manufacturers can easily incorporate weight sensing devices into the gear. Or, weight sensors could be incorporated into a Wheel Chock device. There is no reason for guesstimates.

      • by michelcolman ( 1208008 ) on Monday November 16, 2015 @05:05PM (#50942907)

        First of all, tail strikes on take-off are obviously the result of overrotation, but this usually happens because the pilot rotates at the wrong speed. You pull back, expecting the plane to leave the ground, but instead the plane remains on the ground while the nose keeps going up. Also, you may be running out of runway if the calculations were off, so you'll pull back regardless.

        About the weight sensors: good idea, but this is aviation, where everything has to work reliably in pretty difficult environmental circumstances. Even something as simple as a proximity switch to determine whether or not the gear is down, fails from time to time. We often deal with incorrect tire pressure indications, temperature indications, etcetera. Measuring the weight of a plane with sufficient precision is quite a bit more complex than a simple tire pressure reading, so I can't see any manufacturer trusting that kind of system enough to let it determine take-off settings by itself. Maybe as an extra crosscheck for the data from the loadsheet, sure, but not as the primary source of information.

        People always go "we should replace the pilots with automated systems because pilots make too many mistakes", but they have no idea how many mechanical failures we deal with as part of the routine of our job. We make mistakes, sure. But so does automation.

  • by burtosis ( 1124179 ) on Monday November 16, 2015 @02:12PM (#50941503)
    It still boggles my mind how we live in the Information Age and this data was not automatically uploaded and calculated. I'm not saying it dosent require a human to sign off on, but it's mildly insane it isn't all automatically calculated and simply checked.
    • Re: (Score:3, Interesting)

      by Anonymous Coward

      I don't know for sure, but I believe the pilots are supposed to *only* use the certified avionics systems in the aircraft, but they hate the godawful UIs in those things so they use iPads even though they're really, really, really not supposed to.

      • by jbwolfe ( 241413 ) on Monday November 16, 2015 @03:06PM (#50942085) Homepage
        As long as the device and software (the iPad and app in this case) has been vetted by the regulating agency, it is acceptable to use and may actually be required. I'm unsure of the interface to which you are referring, but takeoff performance calculations are not integrated into any large transport aircraft that I have ever flown. The FMC can only calculate data accurately if its given the correct inputs- stuff like ZFW, CG, flap setting, reduced thrust setting, etc. GIGO

        At my airline, takeoff data calculations are centralized (acquired through datalink) rather than carried onboard, but still require those variables.

        • by MouseR ( 3264 ) on Monday November 16, 2015 @03:45PM (#50942381) Homepage

          The iPad is not at fault here. Pilot did simple math and forgot to carry over a "1". There's no carry over when you let a software add.

          It's a whole system failure: paper being handed out to be hand-computer and then the number punched into a iPad for final trust numbers which are then entered in the avionics system.

          A frickin piezo on the landing gears would have done the trick.

        • by DarkOx ( 621550 ) on Monday November 16, 2015 @07:41PM (#50943965) Journal

          I am not a pilot so I don't know but I am curious. In all the old war novels I read they just run the throttles to "take off power" and go.

          Is there any reason you don't just slam the throttles open on a modern jetliner until you are off the ground? Why do anything other than make sure you are not 'to heavy' to make it before you run out of runway? What not just 'punch it'.

          • by Lisandro ( 799651 ) on Tuesday November 17, 2015 @01:24AM (#50945563)

            There's a good number of reasons for this, and they're not immediately obvious.

            - Optimize fuel usage; you want to burn only as much as you need on takeoff
            - Reduce engine wear as much as possible. Engine overhauls are awfully expensive for airlines.
            - Don't overthrust engines in case of failure. If an engine goes out on takeoff with too much airspeed the airplane might not be able to correct yaw before running out of runway.

            On small piston aircrafts, yes, you usually go full power on takeoff every time. Airlines are a very different beast though.

    • by kybred ( 795293 )

      Yes, why isn't this something the flight system calculates, instead of "There's an App for That"?

      • by kuzb ( 724081 )

        Probably because boeing would charge another $750,000 for that feature.

    • It still boggles my mind how we live in the Information Age and this data was not automatically uploaded and calculated. I'm not saying it dosent require a human to sign off on, but it's mildly insane it isn't all automatically calculated and simply checked.

      Is there some reason they shouldn't just use 100% thrust at takeoff and make sure the cargo being carried was less than the maximum capacity?

      • by es330td ( 964170 ) on Monday November 16, 2015 @02:30PM (#50941729)

        Is there some reason they shouldn't just use 100% thrust at takeoff and make sure the cargo being carried was less than the maximum capacity?

        These engines are optimized for certain turbine speeds. By staying within the recommended ranges they reduce wear & tear and improve efficiency. In addition, max acceleration is harder on the passengers. Think of it like driving a car. Do you accelerate from every stop by pressing the gas pedal all the way to the floor or do you match how much gas you give it to the driving conditions and who and how many people are in your car?

        • Do you accelerate from every stop by pressing the gas pedal all the way to the floor or do you match how much gas you give it to the driving conditions and who and how many people are in your car?

          Sadly, for too many drivers, the answer would be "I floor the gas, going from 0 to 60 in as short a time as possible. Then, I hit the brakes and come screeching to a halt at the red light four blocks ahead of me."

      • by gstoddart ( 321705 ) on Monday November 16, 2015 @02:42PM (#50941855) Homepage

        Is there some reason you don't redline your car before you pull away from a stop light?

        Having pilots who don't know how to do anything other that "rev it up to full speed and let 'er rip" sounds like a terrible idea to me.

        Both for maximizing fuel and not abusing the engines, doing it based on real numbers makes more sense than the equivalent of flooring it.

        • Is there some reason you don't redline your car before you pull away from a stop light?

          My car has traction control, and will behave perfectly nicely if I do that, you insensitive clod! Well, one of them anyway. The most modern one.

      • by Goldenhawk ( 242867 ) on Monday November 16, 2015 @02:55PM (#50941977) Homepage

        I'm a flight test engineer that works on large (passenger-class) aircraft. We do tests related to this issue.

        It actually has a lot to do with takeoff safety, ironically enough. If you lose an engine at high power, the airplane will try to yaw (turn left or right) because the engine(s) on the other side are still producing thrust. At lower speeds, with less aerodynamic forces, the rudder is not capable of keeping the airplane in a straight line. So there's a speed called "Vmcg" - "velocity minimum control ground" - below which you MUST pull back the power on the good engines to avoid going off the side of the runway (you're going to have to stop the takeoff). There's also a speed called Vmca, the airborne minimum control speed (you will start to yaw out of control).

        So with less power on all the engines, there is less asymmetry possible in the event of a failure. With reduced takeoff thrust, you don't need as much rudder at any given airspeed, so your Vmcg and Vmca are both lower.

        This is important for takeoff because if you have a lot of runway available, you can use it by taking longer to accelerate (by having lower thrust). As a consequence, your risk in the event of an engine failure is reduced - you won't head off into the grass if it happens on the ground, and you'll be assured of sufficient control authority if it happens in the air.

        So when an airplane manufacturer builds the "takeoff performance charts", these Vmc speeds heavily factor into the takeoff planning.

        Now, in this tail strike mishap, the lower weight caused the iPad to compute TOO LOW a speed. Lifting off too slow takes more nose-up (pitch) angle; lift goes up as a linear function of pitch angle; lift has to equal weight to go flying. Because of the reduced takeoff thrust, they were already planning to use most of the runway to accelerate - which put them into a corner; they were too slow to take off at the normal pitch angle, but were out of room to stop. So they pulled up until the airplane started flying - which means they pulled up high enough that the tail hit the ground (just barely in this case).

        • by Obfuscant ( 592200 ) on Monday November 16, 2015 @03:15PM (#50942149)
          I wish I had mod points today. Excellent answer.

          Add in the safety factor that a heavy aircraft is better lifting off further down the runway so that the following departures and arrivals of lighter aircraft are less likely to encounter wake turbulence. As a small plane jockey, you always want to take off or land before the point the previous heavy aircraft took off, or after the point the previous heavy aircraft landed.

        • This all makes sense and I too wish I had mod points as I would use them instead of responding. What I don't understand here is how the error wasn't noticed while going down the runway. I'm going to explain this using all of the wrong terminology but hopefully my point comes across. As the plane travels down the runway, the generated lift causes the nose to start to rise at a certain angle. As you get closer and closer to leaving the ground, the pitch rises. My understanding is that the Concorde relied
        • by jbwolfe ( 241413 )
          To add to this and in regard to the model flown here, The -800 and-900 versions are stretched and have higher MTOG. The end result is since the landing gear are just as short, there is even less margin for error with tail strikes. This is true both for takeoff and landing and results in higher rotation speeds as well as higher approach speeds. In some cases, this results in weight restrictions due solely to the needed increased speeds.

          Also of note regarding Vmcg, if Vr (reject) is lower than Vmcg, you're o

    • My guess is that the 737 was built about 20 years ago. The ipad is taking place of what is essentially a circular slide ruler.

      Airliners have had scales built into them for years, but you still need to calculate load based on fuel, passengers and cargo.

      What's concerning is they didn't notice the velocity not rising fast enough to increase throttle. Additionally they didn't have enough intuition to recognize their calculations were way off.

    • by Ichijo ( 607641 )

      And for another layer of redundancy, the plane or the iPad should detect that it isn't accelerating at the expected rate.

    • this data was not automatically uploaded and calculated.

      I know, right? All the sophisticated sensors on an airliner and there isn't one to say your exact weight? The DMV can weigh trucks without stopping at scales now, how is it airlines are still using average passenger and bag weights? This is insane.

  • by QuietLagoon ( 813062 ) on Monday November 16, 2015 @02:13PM (#50941517)
    Where do the pilots get the data? Is it displayed to them? Is it shouted at them as they board the plane?

    .
    Why can't the source of the data convey the data to the tablet apps automatically? Why involve an error-prone human in the process?

    • by Solandri ( 704621 ) on Monday November 16, 2015 @03:18PM (#50942169)
      Because if an automatic system fails in an "obvious" way [wikipedia.org] and causes an accident, people here would be posting "why wasn't a human in the loop?"

      In an ideal world, both automatic systems and people would complement each other with a person manually checking the automatic results. But in the real world, once you automate the system, people tend to get lazy and stop double-checking the automated system's calculations. NASA ran across the same problem - in the post-Challenger investigation they discovered that having multiple inspections actually decreased safety. Each inspector assumed the other was doing his job, so became more lax and sometimes didn't check things thoroughly or sometimes even skipped checks. Even in this incident, the pilot using the iPad didn't bother checking to make sure the number he entered into the iPad was the number he thought he typed. He just assumed the input method worked, despite everyone who's tried to type an email on a touch interface knowing that errors occur frequently.

      So you end up with an either/or situation. Either the system has to be completely automated with the engineers trying to think up every possible scenario during design, and it'll still occasionally fail in ways you never thought of which will lead people to question why humans were left out of the loop. Or it has to be reliant on humans doing everything by hand, to ensure they take their job seriously and actually do it. Unless an automatic system has a track record showing decades of reliability (this is why computers on aircraft are usually more than a decade old), aerospace usually relies on humans.
    • by jbwolfe ( 241413 )
      Obtaining performance data requires knowing how many people and bags and where they are located, which runway is used, flap setting CG and weather data like pressure, winds and temperature. These factors, exclusive of the atmospheric conditions, are dictated by the humans operating the plane and while they could theoretically be automated, there likely isn't enough return on the invested effort to do so.
  • by Anonymous Coward on Monday November 16, 2015 @02:14PM (#50941537)

    So somebody entered bad data into the Flight Management Controller.

    Happens all the time with Qantas, which has been caught out for having extremely lax protocols.

    Search the ATSB database, there have been more than a dozen incidents in the past decade which by pure luck didn't result in mass casualties.

    Then read the BS excuses Qantas gives. Such as "the ladder wasn't tall enough to check the engine cowling was locked".

    • People like picking on QANTAS for this, but the reality is that equal shit happens on all airlines. After all it wasn't a QANTAS plane which recently had the engine cowling fly off mid flight. And I say that for any of the several cases of this happening this year.

  • 5% (Score:3, Interesting)

    by rfengr ( 910026 ) on Monday November 16, 2015 @02:16PM (#50941557)
    Seems to me 5% should be well within the margin or error. Are they trying to save fuel by cutting it that close?
    • Yes that is a ridiculously small margin.... it's not hard to imagine a series of errors adding up to 5%. What about a sudden tail wind?

    • by fche ( 36607 )

      Not just that ... it's weird that the pilot flying didn't monitor carefully enough the rotation angle. Sure, if she rotates early (due to wrong v1/power), there may not be an immediate lift-off -- so dip the nose down and use a bit of the remaining runway. (By this time they're past V1 so are committed to flying instead of stopping.)

    • by jbwolfe ( 241413 )
      Performance data normally has a safety buffer built in. However, a 10,000kg error is not a variable that would fall into the margin or error for performance. The primary goal of reduced thrust is to extend the life of the engine. A secondary goal is to reduce the likelihood of a turbine failure.
  • As if... (Score:5, Insightful)

    by CanadianMacFan ( 1900244 ) on Monday November 16, 2015 @02:17PM (#50941563)

    As if the co-pilot couldn't have made the exact same mistake with a calculator or even paper.

    • As if the co-pilot couldn't have made the exact same mistake with a calculator or even paper.

      The error could have happened regardless of the calculation tool as long as a human is entering the data. Inadequate verification of the information used seems to be at the heart of allowing the error to go unnoticed.

    • by Misagon ( 1135 )

      Sure, but an iPad has a touch-screen. Transposition errors are much more common on touch-screens than on proper keypads where you can feel when you have pressed a key - and where you can feel when you have pressed in-between two keys.
      Real keypads even have a homing dot on the 5 key in the middle to make it easier to find the keys by touch.

      Have you tried touch-typing on a tablet? That is an exercise in frustration, even if the tablet is really large, such as on a MS PixelSense.

    • I don't think it's that simple. It is a lot harder to make a mistake if you can feel the keys.
    • The error was that he pushed the wrong button, which, no, you can't do on paper.

    • In accounting, they would call this an offsetting error. Two mistakes that cancelled each other out but still left the wrong answer. That seems a better name here. A transpositional error would be swapping two digits. $12.32 instead of $12.2.
  • by JoeyRox ( 2711699 ) on Monday November 16, 2015 @02:17PM (#50941571)
    They could have just as easily mistyped the weight using the on-board flight management system's keyboard.
  • by Nutria ( 679911 ) on Monday November 16, 2015 @02:18PM (#50941579)

    Is *not* an "off by one" error.

  • by CanadianMacFan ( 1900244 ) on Monday November 16, 2015 @02:19PM (#50941593)

    you always have both the pilot and co-pilot make the calculations to make sure that they both come up with the same number. That is if you can't have the plane download and measure the necessary inputs in order to calculate the values for you automatically.

    • Re:That's why... (Score:5, Informative)

      by BZ ( 40346 ) on Monday November 16, 2015 @02:35PM (#50941795)

      They did both do the calculation. The pilot did the arithmetic wrong and the copilot typed in his result wrong, and the upshot was that the numbers they entered independently agreed with each other... and were both wrong.

      • Well, to be fair, that's the official report. I'd use Occam's razor and note that if the pilot did the arithmetic wrong and the copilot simply copied the pilot's calculation instead of doing it himself, the records would also match this explanation. Occam's razor cuts to the chase, even as it also cuts to the quick.

  • That is an arithmetic error, not a transposition error.
  • by Rinikusu ( 28164 ) on Monday November 16, 2015 @02:20PM (#50941619)

    I used to be a Ramp Agent at a major international shipping firm. We did weight and balance for the flights. We had several layers of redundancy for our numbers: Every container number and weight was rechecked by another Ramp Agent, and then once again at the gate to match with the load sheets. We realized if we put the numbers in wrong, that could result in loss of life (not to mention aircraft assets and cargo). We took this job very seriously. Once we turned that paperwork (now done via ACARS, supposedly), I would hate to think that the cockpit just fat fingered the numbers in on their end without having a secondary check. "Hey Captain, can we check the numbers real quick?" Probably take them 15-30 seconds at most since they'd be concerned with big picture numbers and not individual positions.

    • Both the captain and co-pilot did separate calculations. They just happened to make two different arithmetic errors that resulted in the same incorrect result, therefore failing to detect the error. The captain failed to carry a 1. The co-pilot type in a 6 instead of a 7.

      What this incident shows is that automation or the use of computers to do calculations automatically, does not necessarily improve reliability. Independent and redundant systems are instrumental in reducing error, but basic vigilance an

      • by Nidi62 ( 1525137 )

        Both the captain and co-pilot did separate calculations. They just happened to make two different arithmetic errors that resulted in the same incorrect result, therefore failing to detect the error. The captain failed to carry a 1. The co-pilot type in a 6 instead of a 7.

        What this incident shows is that automation or the use of computers to do calculations automatically, does not necessarily improve reliability. Independent and redundant systems are instrumental in reducing error, but basic vigilance and attention to detail frequently is the most effective means in preventing mistakes.

        I may be wrong, but in my experience with commercial flights crews the pilots are trained to not only verbalize what they are doing but the other crew member is supposed to visually check and verbally repeat what is being done. So if the captain is putting in 70000lbs into the computer he should verbalize "weight 70000lbs" after which the FO should check to make sure that the entry was indeed "70000lbs" and verbally confirm so. If the weight does not match his calculations or what is in the system does no

    • I might have misread somewhere, but the impression I got is that one pilot fat fingered a number and just so happened to enter the same number that the other came up with by failure to carry a 1.
  • Seriously, at this time, it would actually make sense for the manufacturers to design in weight happening automatically.
    • by Lumpy ( 12016 )

      And they could by putting load cells on the landing gear so the system knows exactly how much it weighs.

      • I'd have thought that adding anything to the landing gear which does nothing to help you land the plane would be a pretty dumb thing to do, engineering wise.

        • by Lumpy ( 12016 )

          Considering that 747's and 777's have them as an option when being ordered means that it's a good idea, engineering wise.
          but then the stupidity of taking off at less than 100% throttle to save a little bit of fuel at the expense of increasing risk is also a pretty dumb thing to do, engineering wise.

          • by Idarubicin ( 579475 ) on Monday November 16, 2015 @04:48PM (#50942775) Journal

            ...but then the stupidity of taking off at less than 100% throttle to save a little bit of fuel at the expense of increasing risk is also a pretty dumb thing to do, engineering wise.

            Taking off at less than 100% throttle means reduced acceleration, which reduces stress on the airframe (and passengers). It reduces wear on the engines and - more important - reduces the risk of turbine failure. It makes the aircraft easier to control (less unbalanced thrust) if it does lose an engine immediately before or after takeoff.

            So...not just to save fuel.

  • Honestly flooring it is always the best option.

  • Siri (Score:2, Funny)

    by chubs ( 2470996 )
    "Okay. I found 5 restaurants like 'calculate takeoff thrust' near you"
  • At least they didn't run out of fuel like they did on the Gimli Glider.
  • Qantas (Score:5, Interesting)

    by Anonymous Coward on Monday November 16, 2015 @02:51PM (#50941955)

    On a recent flight from SYD to MEL our Qantas pilot ranted on the PA about how evil the ATSB was because they wouldn't let the plane take off, because Qantas engineering accidentally put an incorrect black box into our plane. He said that Qantas maintenance made mistakes like that all the time, and that, since it wasn't a safety issue to fly without a black box, the ATSB were just being pricks.

    I will never set foot on a Qantas plane ever agin.

  • A transposition error's what you get when you mistakenly transpose 2 digits when typing a number, ie 5712 instead of 5172. If there's an error in the expected total of a set of numbers and the difference is divisible by 9, chances are good one of the numbers has a transposition error.
    • by T.E.D. ( 34228 )

      First, when working out the plane's takeoff weight on a notepad, the captain forgot to carry the "1," resulting in an erroneous weight of 66,400kg rather than 76,400kg. Second, the co-pilot made a "transposition error" when .... "Transposition error" is an investigatory euphemism for "he accidentally hit 6 on the keyboard rather than 7."

      A transposition error would have been swapping the position of two adjacent glyphs, for instance coming up with "64,600".

      Typing in a "7" when it should have been a "6" in the number "66,400" is a transcription error. Those are very different errors, typically caused by very different things.

  • So human makes calculation on paper. The result is 66,400kg. Human then enters the same number onto a tablet.

    Sure the human involved sucked at math and got the wrong result in the first place, but he copied the (wrong) result into the tablet perfectly fine.

    How does this have anything to do with the tablet?

    (yes, all this stuff should probably be automatically generated in this day and age, but that is a different discussion to have)

  • Imagine dying because someone fat fingered some figures on an iPad? I think most of us can testify that we are more likely to make a typo when typing on a touchscreen. Oof! Now the part with forgetting to carry the one is a whole 'nother issue. heh

  • by gurps_npc ( 621217 ) on Monday November 16, 2015 @04:10PM (#50942523) Homepage
    Before you drive a 10,000 lb truck over a bridge, you make sure it is rated for 10,000 lbs.

    That does not mean it can handle 10,000 lbs, it means it can handle MORE than 10,000 lbs - the excess is called a margin of safety. It can be expressed as a "factor of safety". If your factor of Safety is 2, then the engineer believes the bridge can handle twice the stated load.

    For aircraft and spacecraft, the US government generally requires Factor of Safety of at least 1.2, but as high as 3 is common. That means that if the tire is expect to hold 10 tons, it was built to actually hold at least 12 tons. (All above info from Wikipedia)

    Apparently the idiots that write these programs thought, hey, we don't need to use a reasonable Factor of Safety. They calculated they needed 93.1 units of thrust, but failed only 88.4. That means their Safety Factor was less than 1.12

    If the morons had put in the expected margin of safety of 1.2, then the plane should have been able to take off even if they had only applied 77.67 units of thrust.

    Clear failure of the programmer to build a sufficient margin of safety into their calculations

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