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Was Flight Ban Over Ash an Overreaction?

Posted by timothy on from the in-his-unbiased-opinion-of-course dept.

HaymarketRiot writes "Richard Branson has claimed that the flight ban, due to the eruption of the volcano Eyjafjallajokull, was an overreaction on the part of the authorities. Britain's government has even called for the airlines to be compensated. This does look like a perfect excuse for already greedy airlines to try and get more money ... any experts care to comment on the effect of volcanic ash on planes?"

8 of 673 comments (clear)

  1. From what I've heard, it really is that bad... by seebs · · Score: 5, Informative

    Basically, the jet's internals are hot enough to melt rock back into glass... So after a couple of passes through ash clouds, you have a thin layer of glass covering all the internal turbine blades. Which completely destroys the engine, and is extremely hard to repair without completely replacing the blades.

    So, basically, what I've been told is that, yes, flying a jet through a volcanic ash cloud is a good recipe for completely destroying the engines, such that they need to be rebuilt, within two or three passes through the ash. It sounds plausible, and I've not yet heard anyone who actually does aircraft maintenance or anything like that suggest that it's harmless.

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    1. Re:From what I've heard, it really is that bad... by BagOBones · · Score: 5, Informative

      Exactly, I am not sure why past tragedies have not been mentioned by ANY of the officials or NEWS networks..

      I remember seeing something about this on Discovery or History channel years ago and a quick search pointed me to British Airways Flight 9 on Wikipedia, all four engines FAILED!

      http://en.wikipedia.org/wiki/British_Airways_Flight_9

      --
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    2. Re:From what I've heard, it really is that bad... by russ1337 · · Score: 5, Informative
      Agree, and the argument is more fundamental than that.

      Federal Aviation Regulation 25.1309 relates to airworthiness standards for aircraft, and the fundamental aspect of this regulation is system safety. Excerpt below, with emphasis:

      (a)The equipment, systems, and installations whose functioning is required by this subchapter, must be designed to ensure that they perform their intended functions under any foreseeable operating condition.
      (b) The airplane systems and associated components, considered separately and in relation to other systems, must be designed so that--
      (1) The occurrence of any failure condition which would prevent the continued safe flight and landing of the airplane is extremely improbable, and
      [(2) The occurrence of any other failure condition which would reduce the capability of the airplane or the ability of the crew to cope with adverse operating conditions is improbable.

      Firstly, Aircraft are not designed to fly through clouds of corrosive silica ash.

      Secondly, 'Extremely improbable' is defined in the Advisory Circular (AC 25.1309) to that regulation, which requires chance of catastrophic loss to be less than "extremely improbable" or "1x10^-9" chance of total loss. Techniques such as Fault Tree Analysis are used to allocate reliability of systems to sub-systems, so the entire aircraft can be built from components with realistic reliabilities. However, the volcanic ash offers a 'common mode' failure across all engines including gas turbine Auxiliary Power Units.

      The regulators have an obligation to ensure the chance of total loss of an aircraft due to flying through an ash cloud remains 'extremely improbable', i.e 1x10^-9.

      Also, if the airlines lost an aircraft because they were allowed to go flying, and were being sued by the families of the victims, they'd be screaming blue murder at the regulators saying they didn't do enough to protect the airlines.

    3. Re:From what I've heard, it really is that bad... by leetrout · · Score: 5, Informative

      I think it's worth specifying that the wind screen becoming opaque wasn't from ash sticking to it, but was from the ash sand-blasting it. It had the same effect on the landing lights and with this incident happening at night, added yet another level of difficulty to the situation.

  2. Boeing says it's not a good idea. by Moofie · · Score: 5, Informative

    Don't know if you put any stock in what an aircraft manufacturer might say on the subject, but...

    http://www.boeing.com/commercial/aeromagazine/aero_09/volcanic_story.html

    Summary: If you find yourself flying into an ash cloud, turn around immediately.

    So, yeah, maybe Branson wants a check, but flying into ash clouds is a very bad idea. And they don't show up on weather radar.

    --
    Why yes, I AM a rocket scientist!
  3. Re:Engines stalling enough for you? by gyrogeerloose · · Score: 5, Informative

    Hey moderators--look a little more closely and you'll notice that the so-called flamer and the person he flamed were the same people!

    --
    This ain't rocket surgery.
  4. Aerospace Engineer Angle by knapper_tech · · Score: 5, Informative

    The cooling system used in gas turbines (jet engines) is very sophisticated and necessary to keep the superalloy blades from creeping too fast. The system consists of bypass air channeled through the blades and exhausted through tiny perforations, creating a layer of cooler air between the blade and the hot flow from the combustor. Furthermore there are two ceramic layers on the outside of the blade. One to prevent oxidation. One to slow heat transfer (insulate). As has been mentioned in other articles, the cooling pores could get clogged by the ash. I also suspect the coating might fail if impacted by ash. If the coating fails or otherwise reacts with the ash, then you can definitely have a problem.

    If the blades get just a few tens of degrees hotter, they will surely fail. There's not a lot of margin for error with jet engines. Through good design and manufacturing control, we've managed to make gas turbines extremely reliable, but ash is not a design condition at all. It's abrasive, might react with the coating, and might accumulate on the blades, changing both their mass and aerodynamics.

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  5. Re:I am no expert ... by Maxmin · · Score: 5, Informative

    That's an apple-oranges comparison. The video shows a GE-Honda HF120 turbine, a 2,000 lb two-stage, two-compressor turbofan designed for the light jet market. A very different design from...

    Commercial airline engines are rated from 14,000 (old-school Boeing 737) to over 100,000 (Boeing 777) pounds.

    Aside from that, the difference in scale of a fine volcanic ash particle compared with a grain of sand determines the melt rate. Volcanic ash passing through a turbine is essentially a fluid, one that melts at around 1000 C. Aggregate sand (in the video) melt between 1500-1700 C.

    Turbofan combustion chambers burn at between 1500-2000 C. Grains of sand are too thick to melt, given the airflow rate through an engine (250-1400 mph.)

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