How Much Volcano Slag Can A Jet Engine Take?

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.caa.co.uk/default.aspx?catid=2011 &

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!

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.