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Guru

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### How Much Volcano Slag Can A Jet Engine Take?

05/23/2011 6:19 PM

I heard on a TV program this evening that the volcanic ash density limit for flying is now 4000μgm-3 (raised from last year's limit of about 2μgm-3 I think - tho' I was only half listening to that bit - I've verified the new limit).

I had a quick look round, but couldn't find much definitive info. about what volume of air an airliner engine takes in per second.

Strikes me that 4mgm-3 could maybe build up to several kg of ash in a few minutes.

Looking for a handle on it - any thoughts?

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Guru

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#1

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/23/2011 7:24 PM

I think it has more to do with accumulation than ingestion. Kind of like prop icing.

Fly around, or go back.

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#2

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/23/2011 7:44 PM

I'd assume most of it would just shoot through. Just wondering what the threshold is for build-up in the engine (assuming that's what happens).

D'you know what mechanism stopped the engines in previous events? I seem to remember reports of planes falling out of the sky with total engine cutout - but fortunately picking up after losing a few thousand feet.

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#3

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/23/2011 8:22 PM

I don't know, but I'd guess it was oxygen starvation that flamed the engines out.

Nothing else I can think of would be reversible without an engine teardown, on the ground.

FIOE or AH may have opinions.

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Associate

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#5

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/24/2011 10:36 PM

As far as I remember, the earlier engines shut down due to severe erosion of the turbine blades, reducing the compression ratio / thrust. by descending, the higher atmospheric pressure/ increased oxygen content allowed a restart.

Guru

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#6

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/24/2011 10:51 PM

Correct,

the ash particles re-melt in the combustion chamber and solidify onto the turbine blades until the airflow is disrupted sufficiently for the fires to go out!

With the 747 which suffered 4 flameouts over the Indian ocean some years ago - as the aircraft glided the turbine blades cooled sufficiently, as I understand it, to shrink a little and enough of the accumulation flaked off due to differential expansion to enable them to re-start the engines when they reached sufficiently dense air, but this is not a given! - it cannot be relied on!

The other problem was that the ash, being abrasive sandblasted the windshield opaque !!!!

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#4

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/24/2011 1:45 AM

The potential damage would be roughly proportional to ∫(concentrationt dt). Assigning a limit of 2μgm-3 or 4000μgm-3 seems arbitrary, since duration of exposure is equally important.

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Guru

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#7

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 12:05 AM

John,

Not so much on the engine effects but there is a fair bit of info on the volcano atmospherics vs flying conditions at

http://www.metoffice.gov.uk/volcano/public/natlantic.html

including this info which may be interesting

The three levels of ash density are defined as:

• Area of Low Contamination: An airspace of defined dimensions where volcanic ash may be encountered at concentrations equal to or less than 2x10-3 g/m3, but greater than 2x10-4 g/m3.
• Area of Medium Contamination: An airspace of defined dimensions where volcanic ash may be encountered at concentrations greater than 2x10-3 g/m3, but less than 4x10-3 g/m3.
• Area of High Contamination: An airspace of defined dimensions where volcanic ash may be encountered at concentrations equal to or greater than 4x10-3 g/m3, or areas of contaminated airspace where no ash concentration guidance is available.

PILOT RESPONSE
WHEN ENCOUNTERING A VOLCANIC CLOUD

Recognising a volcanic ash encounter
Note that airborne weather radar does not detect volcanic ash, and low
concentrations may not be detected by the crew. The following are a list
of symptoms which may be expected if volcanic ash is encountered:
a) Odour: When encountering a volcanic ash cloud, flight crews
usually notice a smoky or acrid odour that can smell like electrical
smoke, burned dust, or sulphur;
b) Static discharges: An electrostatic phenomenon similar to St.
Elmo's fire or glow can occur. In these instances, blue-coloured
sparks can appear to flow up the outside of the windshield or a
white glow can appear at the leading edges of the wings or at the
front of the engine inlets;
c) Changing engine conditions: Surging, torching from the tailpipe
and flameouts can occur; engine temperatures can change
unexpectedly and a white glow can appear at the engine inlet;
d) Engine restarts: Engines may accelerate to idle very slowly,
especially at high altitudes (could result in inability to maintain
altitude or Mach number);
e) Haze: Most flight crews, as well as cabin crew or passengers, see
a haze develop within the aircraft; dust can settle on surfaces;
f) Airspeed: If volcanic ash fouls the pitot tubes, the indicated
airspeed can decrease or fluctuate erratically, with associated
effects on aircraft systems;
g) Pressurization: Cabin pressure can change, including possible loss
of cabin pressurization;
h) Landing lights: Can cast sharp distinct shadows;
i) Cockpit windows: Possible loss of visibility due to windows
becoming cracked or discoloured due to the sandblast effect of the volcanic ash

Might be safer to use the ferry!

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#8

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 3:35 AM

I'll give masu a nudge - he explained a lot of the mechanisms last year. The accretation issue is that one that causes the biggest problem inside the engine...molten ash solidifies like glass on the blades.

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#9

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 7:16 AM

I've never seen a teardown report on a damaged engine. Has anyone? My phrasing, since I'm not an AP.

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#10

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 7:44 AM

G'day folks,

There's not much more that I can add to this other than the flight that had a four engine failure was British Airways Flight 9 flying from Jakarta to Perth when it encountered the volcanic ash cloud that was being thrown up from the eruption of Mount Galunggung.

Also the process that causes the engines to fail comes about from the ash melting in the combustion chambers then solidifying on the turbine blades. Ultimately the build-up messes with the profile of the turbine blades and they can no longer drive the compressors so the engine flames out.

The thing that saved BA-9 was that as they descended they both dropped below the ash cloud and the cooling of the turbines cracked off enough of the glass like build up for the engines to restart. However when they got the engines going again and they started gaining height they ended up back in the ash cloud and started to have the same problems again. Fortunately cool heads prevailed and they managed to limp the aircraft back to Jakarta which is when they found that the windscreen had been sandblasted opaque. Just the make things more difficult for the flight crew the glide slope indicator at Jakarta wasn't working so with the limited visibility they had landing was to say the least somewhat difficult. Apparently the captain noticed that there was a clear area around the edge of the windshield so he used that to land the aircraft.

If you can find it there was an episode of Air Crash Investigation (series 4 episode 2 "Falling From The Sky") on the subject.

PS: I forgot to mention that the current limits are intended more to prevent long term damage to engines than the sort of total engine failure that happened with BA-9. Such damage could be minor but like most things with aircraft accidents it's never one thing that causes an accident and undiagnosed engine damage due to volcanic ash ingestion could come back to bite you at a future date.

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#11

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 8:17 AM

An interesting read of engine details after volcanic ingestion

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#12

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 9:15 AM

I might add...that because of that flight new sensors are installed that can detect the ash. That flight had no idea they were actually in a cloud of ash. When it did land the windows and any leading edges of the plane looked sandblasted.

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#13

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 3:53 PM

According to that report, there were no external signs of distress, no engine anomalies or abnormal operating data. Where did you see that there was physical damage to the aircraft windows or leading edges?

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#14

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 4:02 PM
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Guru

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#15

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 4:09 PM
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Guru

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#16

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 4:27 PM

Ah, my bad Fredski. I was referring to the report in #10, (NASADC8), which someone kindly posted replying to my inquiry about engine damage, and of course you are referring to BAA009, the subject of this thread. Can you believe these things don't crash? Modern aircraft are superb.

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#17

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 4:58 PM

Not a problem. It's all interesting to me regardless of the thread.

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#18

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 5:03 PM

"... BAA009, the subject of this thread".

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Guru

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#20

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 10:53 PM

blow something

Off Topic (Score 6)
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#19

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/25/2011 7:21 PM

Two different aircraft, two different flights:

1. BA flight over Indian ocean - 4 flameouts, sandblasted windscreen, aircraft damage

2. NASA research flight north of Iceland, much thinner ash cloud no obvious damage but \$3+M to repair the engines......

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#21

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/26/2011 5:40 AM

The thing that I find disturbing in the NASA report is that if it was a normal aircraft without the special sensors they most likely wouldn't have noticed that they flew through the ash cloud yet there was still severe engine damage, i.e. clogging of the cooling holes in the turbines, that would have more than likely resulted in engine failure within another 100 hours of operation.

Imagine that, flying along unknowingly with four damaged engines and having them fail due to something that happened to the aircraft some 100 flying hours before.

Now that's even more frightening than BA-9.

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#22

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/26/2011 6:43 AM

Ryan Air says it is not a problem.

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#23

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/26/2011 5:55 PM

Michael O'Leary is a twat.

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Guru

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#24

### Re: How Much Volcano Slag Can A Jet Engine Take?

05/27/2011 12:54 AM

That is a rather polite way to describe the clown

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