Why Planes Need to Avoid Fine Volcanic Ash

Posted on April 15, 2010  Comments (3)

Volcanic ash: why it’s bad for planes

Aircraft avoid any airspace that has volcanic ash in it for a simple reason: the ash can wreck the function of propeller or jet aircraft, because it is so fine [less than 2mm in diameter, and some as fine as 6 microns] that it will invade the spaces between rotating machinery and jam it – the silica melts at about 1,100C and fuses on to the turbine blades and nozzle guide vanes (another part of the turbine assembly), which in modern aircraft operate at 1,400C.

That, in turn, can be catastrophic – as the crew of two aircraft, including a British Airways Boeing 747, discovered in 1982 when they flew through an ash cloud from the Galunggung volcano in Indonesia. On both planes, all four engines stopped; they dived from 36,000ft (11km) to 12,000ft before they could restart them and make emergency landings.
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The Icelandic plume has been thrown to between 6km and 11km into the atmosphere – exactly the height that aircraft would be flying.

Passengers on the BA flight that hit the cloud in 1982 said the engines looked unusually bright: soon after all four flamed out. “I don’t believe it – all four engines have failed!” said the flight engineer. The crew were prepared to ditch, and the captain told the passengers: “Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines have stopped. We are doing our damnedest to get them under control. I trust you are not in too much distress.”

Luckily, three of the engines could be restarted. The plane landed safely, and nobody was injured.

Related: Why Planes Fly: What They Taught You In School Was Wrong – Successful Emergency Plane Landing in the Hudson River – Engineering Quiet, Efficient Planes – Engineering the Boarding of Airplanes

3 Responses to “Why Planes Need to Avoid Fine Volcanic Ash”

  1. Tim Glaze
    April 19th, 2010 @ 9:02 am

    There seems to be a disconnect between the overly simplistic assertion why to avoid ash-clouds, and the BA experience. As the BA crew were able to restart the engines, the alleged damage likely did not occur. The conventional reason is that ash is abrasive, and therefore, significantly wears parts of the engine, and this wear deforms the requisite aerodynamic shape of essential components, whether a propeller or a compressor blade.
    The most likely cause of the BA engine stoppage was extinction of ignition. Once the ash cleared the combustion chamber, restart was possible, given the sufficient altitude.

  2. mike
    April 20th, 2010 @ 11:27 am

    I think we’ve been a bit unlucky this time (or extremely lucky in recent history) that the glacier cooled down the ash which led to the small particles of glass being created and thrown up with the ash into the atmosphere. By the same token am getting a bit fed up of airlines pushing the financial imperative to fly – and at times seeming to dismiss the safety concerns held by the majority of travelers, such as myself.

  3. Dana
    April 22nd, 2010 @ 10:45 pm

    “Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines have stopped. We are doing our damnedest to get them under control. I trust you are not in too much distress.”

    REALLLYYYYY, they hoped people weren’t in TOO MUCH DISTRESS? Was this guy serious? NO, they were NOT in distress, they were crapping their pants after such a plunge!!! LOL

    I am sorry, I know this is a serious matter, but that quote really bothered me. I just can’t picture a Captain actually saying something like that. I guess after the heroic efforts on behalf of Capt. Sully on the Hudson, I would just expect pilots to try to keep the passengers at ease. Then again it was in 1982 EONS ago (in aviation history that is)!!!LOL

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