Sabenaboy:
Sunfish, could you enlighten us please and give us ONE example of an aircraft that had extremely costly damage to the engine, after flying through an ash cloud so thin that it wasn't noticeable to the eye! Just ONE example! PLEASE...!!!
This has already been posted, but as a courtesy:
The National Aeronautics and Space Administration (NASA) DC-8 airborne sciences research airplane inadvertently flew through a diffuse volcanic ash cloud of the Mt. Hekla volcano in February 2000 during a flight from Edwards Air Force Base (Edwards, California) to Kiruna, Sweden. Although the ash plume was not visible to the flight crew, sensitive research experiments and instruments detected it. In-flight performance checks and postflight visual inspections revealed no damage to the airplane or engine first-stage fan blades; subsequent detailed examination of the engines revealed clogged turbine cooling air passages. The engines were removed and overhauled. This paper presents volcanic ash plume analysis, trajectory from satellites, analysis of ash particles collected in cabin air heat exchanger filters and removed from the engines, and data from onboard instruments and engine conditions.
Even though this was a diffuse ash cloud, the exposure was long enough and engine temperatures were high enough that engine hot section blades and vanes were coated and cooling air passages were partially or completely blocked. The uncooled blades still performed aerodynamically but necessitated expensive overhauls. The insidious nature of this encounter and the resulting damage was such that engine trending did not reveal a problem, yet hot section parts may have begun to fail (through blade erosion) if flown another 100 hr.
Read the rest and look at the pictures yourself:
http://www.alpa.org/portals/alpa/vol...8AshDamage.pdf
Why is it that some people have to put down others who have a different conviction or opinion??? That's how wars start! Can't you simply agree to disagree?
Sabenaboy, we are not talking about "opinion" as in informed opinion. The engine manufacturers, airframe manufacturers, airlines, met offices, regulators, insurers and lawyers have consulted and determined the new set of rules which may be modified by further experience and research. Just because someone says words to the effect "Well I can't see what the problem is" does not make it go away.
Furthermore, the precautionary principle dictates that until we are totally certain about the levels of acceptable risk that we err on the side of caution.
Pace:
On what basis are you making such sweeping assumptions? Do you think the Airlines who are prepared to fly in low levels of ash pollution are also so stupid that they have not weighed up the potential engine damage costs (if infact they do get significant engine damage in their fleets) against the losses they would incur by as you put it "occasional airspace closures"?
They have already operated in low level ash and to date I have not heard of significant damage. I am sure if there was they would be the first to ground their own fleets on a cost basis.
I do not know what your background is to make such assumptions over what the airlines have decided to do with their own level of operational knowledge.
I do not know long term what the costs will or will not be but I guess neither do you. It will not be our problem if you are right but I am sure the airlines will have weighed up all the risks and costs when deciding to operate in low level density ash.
I'm not making any sweeping assumptions at all. Read the NASA report in full please.
The basis of my comments are Five years(some time ago) as a Professional engineer in an airline maintenance department where one of my tasks involved the logistics of providing and positioning spare engines around the network. I also spent another Two years in an aerospace company that among other things assembled engines and made turbine blades and other componentry. While I am now well and truly out of that loop, I've visited and done business with both GE's civil and military engine people as well as Pratt and Whitney Canada and P&W at Hartford. The engineers at those places are not stupid. If they say no more than 2000 micrograms of ash per cubic metre that's good enough for me.
As the NASA report states, the damage to the hot section is insidious and given the number of flights across the Atlantic an encounter with a large scale ash cloud by the Atlantic "fleet" could easily end up grounding hundreds of aircraft for engine changes. Given that the penalty for not grounding an aircraft for a few days will be weeks out of service, I'm not surprised that airlines are complying with the recommendations.
Furthermore,
the insidious nature of the damage alluded to in the NASA report means that you won't find out about it until it is too late
As for costs, and having done entire airline engineering maintenance budgets for Five years, I can safely say that the cost of pulling and overhauling engines at intervals far less than their expected time in service plus the out of service time for aircraft caused by the inevitable backlog of engine work, will dwarf the costs of grounding an aircraft until the danger is past.
I'm sorry is these facts are unpalatable to you but that's it.