Your argument is based on an assumption that airlines are too stupid to recognise this, and therefore need civil servants to tell them what they can and cannot do.

NASA has posted an example of satellite and lidar observation of ash clouds for 16 May.

As NASA puts it

Nighttime Ash Tracking with CALIPSO : Image of the Day

The civil servants are did what the airlines and manufacturers told them to do they set the standards. They modified them quick enough when it started costing money.

John

This appears to be the biggest problem we have with the current methods of determing ash in the atmoshere.

If its dense it can be seen both by the pilot and by satellites. Setting any very low acceptable ash levels is going to cause a major problem of locating where they are by the simple fact that they cannot be seen.

As such we rely on computer and mathematical modelling which may hold X ash concentrations but may also hold X+Y or X-Y or infact no X at all.

Without analysing millions of test shots of air over huge areas we dont know.

Maybe the best way would be to scrap the minimal acceptable levels altogether and to use the satellite visible charts with a safety area around those visible dense ash concentrations.

On the basis that if you cannot see it its unlikely to hurt you aircraft flying in the computer generated low ash areas which are not visible and where ash may or may not be present should be monitored on a more regular basis until we do know more? but with NO meaningless limits

Pace

I think Sunfish's argument is based on the fact that airlines sometimes do things which are not necessarily optimal for safety, for a number of reasons (in order to maintain market share, when everyone else is doing it, for example). It is appropriate for a regulator to step in when it judges that that is happening.

Indeed, that is still one of the most frequent comments about U.S. airline deregulation, that safety has suffered as a consequence (that is not necessarily my view; I am merely pointing out that some hold it).

In the current situation, it would be very hard for an airline not to fly, even if it judges that it is not wise to do so, if everyone else is flying. The airline would instantly lose all market share.

PBL

What like flying in areas of thunderstorm activity, like flying approaches and departures with surface winds above 0, like flying in the bird migration seasons or into and out of coastal based airports etc etc etc :ugh:

Safety has to be based on a demonstrable threat there is no demonstrable threat from a light ash encounter only a percieved possible threat. There may be ??? a financial cost threat but as yet not even that is bearing up to scrutiny.

Pace

Oh dear..... misinterpretation and sometimes misrepresentation are a bit of a safety hazard around here!

I NEVER suggested that any UAVs should fly in or near air routes.

If you want to run the line that UAVs will never be allowed in 'civil airspace' without defining what exactly you mean by that: ie. any bit of sky not specifically defined as 'military'? or what? Noting for a moment that Predators based at Bagram MUST pass over, under or through some 'civil' airspace in Afghanistan to get to where they need to go.....

I've no idea how this actually gets regulated inpractice but a knee-jerk 'Never until rules submitted in triplicate and signed off by God (or at least the Pope)' won't ever be helpful. I guess it depends what your 'medium term' is. But I assume you don't mean 'a month or two'. Believe me, if UK National Security was truly an issue and UAVs were the correct response, they would be whizzing round your ears by next week! I was tempted to add 'Get over it' but somehow resisted!

Appreciate your knowledge on turbine blades, do you know how many there are on a Piper, or a microlight, or a glider ? Those folks running the regulator probably don't - in fact some are on record as stating "‘I know nothing about aeroplanes".

But you know, don't you ? So you must know what the other unspoken risk of VA is that grounded all these aircraft along with the jets ?

"measured" ? "proportionate" ? More like knee-jerk, incompetent, a**e covering. (unless you can enlighten us as to the VA risk to gliders ?).


<begin rant>
And as to the "minimised disruption" - you are having a laugh.

The regulators and governments meanwhile did absolutely **** all to help for several days until shamed into action by the media. Even then it was pathetic - over a week IIRC to get five or so coaches out of Madrid and a navy ship that they decided could take a whole 250 people from Santander (until the commander probably torpedoed the rest of his career by taking more). Tour operators were moving convoys of 30 coaches at a time inside a couple of days, and chartering ships for 2000 pax at a time.

Politicians talked out of one orifice about "dunkirk spirit" whilst effectively ordering the closing the channel ports to small boats trying to get people across (can't cross the channel on small private boats these days apparently - watch out GA, you'll be next). Immigration staff (presumably idle) at airports were not deployed to sea ports, resulting in queues hours long and broken onward transport arrangements. UK immigration at Calais was so well organised that our coach was sent through it twice (while ferry staff were counting down the minutes to departure).

"minimised disruption" ? Actively hindered anyone elses attempts to do so is more like it.

The whole affair was a classic example of our overstuffed EU/UK bureaucracy which has no plan, no clue, and no ability to respond other than by getting in the way.

<end rant>

Entertaining rant but you're wrong about the EU. Initially they had no mandate to get involved, when they stepped in over the first weekend to clear up the mess that the national authorities were making of it (and a lot of highly placed bureaucrats racked up a lot of weekend overtime) things started to happen with some rapidity.

The British Health and Safety disease.

Belt, braces, AND DON"T STAND UP !:=

Infrequent:

You may have a point about piston engined aircraft and gliders. Last time I looked, the Piper I fly had an airfilter, but hey! the aircraft is hired so what do I care anyway? A little ash exposure might help the rings seal and save me a honing job.

When I studied risk management as an engineer and later when I had to apply it in an airline engineering department, we worked on facts. In the absence of facts regarding the likelihood of exposure to some quantity of ash by large numbers of aircraft, the regulator acted promptly and grounded the fleet until the available facts could be marshalled and discussed by people with the relevant expertise and experience. They did this promptly, efficiently and responsibly in a matter of weeks.

The fact that the regulators response didn't suit some of you is irrelevant.

As for comments about "commercial considerations" and individual airline decision making those are also way off the mark. Aircraft Insurance contracts and lease agreements would most definitely preclude doing anything not approved by a regulator, which is probably why Ryanair so promptly grounded its fleet in my opinion.

To put it another way: You would all be screaming about why the regulator didn't ground aircraft if half the fleet was now ash damaged and out of action for months.

I'd like to offer an analogy to VA that I think is illuminating, because there are similarities. That analogy is SLD (Supercooled Liquid Water Droplets).

Unlike VA, SLD has been linked to actual hull losses.
Similarly to VA, there are NO accepted criteria for SLD.
The only advice any OEM gives anyone regarding SLD is the same as that for VA a month ago - avoid at all costs.
There is no reliable means today for detecting SLD, or VA, onboard an aircraft. In certain circumstances visual detection of either may be possible, but is assured in neither case.
Our ability to reliable predict SLD or VA is, in a word, unreliable, in both cases normally for lack of accurate data about the atmosphere.

To date the situation with SLD constitutes a (barely) acceptable risk - although it's been an issue of contention between FAA and NTSB for years. Industry and the regulators have been trying to come up with workable means to handle SLD since Roselawn, in earnest, and have got not very far. We've largely "got away with SLD" because it tends to be a localized event.

So, regarding the comparisons:

IF we've lost a number of aircraft to a known but rare phenomenon (SLD) and havent managed to significantly mitigate the risk, what chance was there really of anyone being any more prepared for the VA issue of the form it took last month? And, realistically, what chance is there of being any more prepared a decade hence?

AND, suppose some unusual weather pattern happened to generate large areas of likely or possible SLD. Would that really leave authorities any choice but to close the airspace which represented a significant risk of SLD?

Oh, and before someone cites the existing icing regs: the environmental data they ultimately rest on is OLD and geographically concentrated, and may be unrepresentative of world-wide conditions today....

Sunfish

Your arguments are tiresome and not borne out by fact but only by your own imagination.

Your opinions have been registered, just like the rest of us. Hopefully you can't go on and on arguing to convince others by citing the same old "what ifs" that can not be backed by facts.

Regulations are codified, judgements are not.

His argument is the one followed by the authorities. He's right. Its not his imagination, its reality that VA shuts down airspace - he doesn't have to prove anything becuase he is simply explaining what is happening and will happen in future.

Refusing to accept the explanation of why its happening isn't an 'argument' or 'discussion', it simply a refusal to accept reality.

Peter We

The above is not Sunfishes arguement at all neither have I seen one posting which disputes what you say above.

The arguement has been about HOW MUCH airspace is closed and what level of ash is acceptable to fly in?

That ranges from ZERO which some argue for up to the maximum dense stuff which billows out of the volcano mouth which no one but a fool would enter.

My own position is that if I can see and eye ball pollution clouds or dense mist and avoid then it will not harm me. It may harm the bank balance long term in clear air with low ash levels but to date there is ZERO evidence to back that up!!!

So really the arguement has been over low density levels of ash.

We have also argued about computer and mathematical ash movement forecasts which have also been innacurate infact some may even argue Dangerous as they give FALSE confidence of where ash may or may not be.

Sunfish has argued the doomsday scenario of 100s of engines all requiring rebuilds at the same time. He has absolutely NO evidence to back that up.

Neither has anyone any evidence whatsover through history that low levels of ash are any threat to safety.

Until that evidence raises its head any restrictions other than NOT to fly in visible ash clouds or mist will just ruin our industry and jobs which I have a sneaking feeling that some here want (not directed at you) especially when those restrictions are not based on a demonstrable safety threat.


Pace

I don't agree with any of this.

This is supposed to be a discussion of an important issue in commercial aviation. It would help if people accurately evaluated the contributions of the discussants.

In my previous post http://www.pprune.org/rumours-news/4...ml#post5706296 I pointed out that for a risk evaluation, even a superficial one, four quantities were needed, which I labelled (a), the chance that current levels of ash posed no risk; (b) the damage which ensues if current levels pose no risk; (c) the chance that current levels of ash pose some risk; (d) the damage that thereby ensues. I pointed out that the risk is (a)x(b) + (c)x(d).

This is the way risk is assessed and has been for 299 years, and there is nothing anybody here can say that will change this.

Pace argues that (a) is 1 and (c) is 0. But he also agrees that, at some unknown level of concentration, (a) will no longer be (1) and (c) no longer 0.

Now, of course, the second term is not really a simple multiplication, but a sum: (c1)x(d1) + (c2)x(d2) +... + (cn)x(dn), where c1.....cn represent classes of concentration and d1,...,dn different levels of damage.

Sunfish's contribution to this assessment is to point out the various levels of damage that can ensue (the d's), and that many of those chances, the c's, are unknown, but that some of them can be estimated from history and science.

Mad(Flt)Scientist has pointed out inter alia that it is fruitless to expect those chances to be well-known in detail, by comparison with a case heshe considers broadly similar, that of SLD's.

I don't find any of this "tiresome". I find it essential to an appropriate risk assessment.

PBL

PBL

I do not question your arguement on risk! but if you read my previous posts you will see there are FAR greater demonstrated risks with a long history of fatal accidents which we do accept and think little of.

Ash todate has a couple of unfatal incidents in dense ash at night and no reported incidents in light ash in over 50 years and millions of flights.

The percieved threat and thats all it is does not warrant the restrictions and financial hits that light ash has caused.

If you want to avoid being killed in an aircraft then dont fly as there is always an element of risk.

Ash in low density is one of the tiniest risk situations and doesnt justify the reaction it has generated or the financial damage to the aviation industry it has created much of which has been media generated hype and scaremongering.

I can point you in many areas of aviation which do hold a far higher risk element and proven risk element if you want to improve safety but it aint ASH

Pace

This is true. Indeed, it is well accepted as a general phenomenon.

Before he was appointed to the U.S. Supreme Court, Justice Stephen Breyer wrote a book "Breaking the Vicious Circle" (Harvard U.P., 1993), based on his Oliver Wendell Holmes lectures at Harvard, in which he includes in Table 5 (pp 24-27) the risks and cost-effectiveness of U.S. federal legislation selected from Fiscal Year 1992. The cost per premature death averted ranges from $100,000 in 1990 dollars (widely regarded by many to be a bargain) to $5,700,000,000,000 (yes, you read that right). About half the measures lie over $8,000,000 per premature death averted, which is regarded by almost everybody who deals with these issues as very expensive.

Cass Sunnstein has a similar, but shorter table in Chapter 2 of his study "Risk and Reason" (Cambridge U.P., 2002), in which he says "it is well-known that there is a great deal of variability in national expenditures per life saved."

Both Sunstein and Breyer deal with the question of how to approach this and other phenomena.

So now we are agreed on this phenomenon, what is your argument to get from the phenomenon of variability of response to risk (on which we agree) to the conclusion that flight should not have been restricted (on which we don't agree)?

PBL

PBL

Your response deserves a carefully though out reply which I will enjoy giving but sadly I have to do what I talk about too much see you couple of days ;)

Pace

Iceland Issues Second Warning on Katla
 

Today, May 27th - Iceland Issues Second Warning on Katla, from:

2nd Iceland volcano issues ominous warning - Europe- msnbc.com -
A second, much larger volcano in Iceland is showing signs that it may be about to erupt, scientists have warned.

Since the start of the Eyjafjallajökull eruption, which caused cancellations of thousands of flights in Europe because of a giant ash cloud, there has been much speculation about neighboring Katla.

An initial research paper by the University College of London Institute for Risk and Disaster Reduction said: "Analysis of the seismic energy released around Katla over the last decade or so is interpreted as providing evidence of a rising ... intrusive magma body on the western flank of the volcano." "Earlier seismic energy release at Katla is associated with the inflation of the volcano, which indicates it is close to failure, although this does not appear to be linked to seismicity around Eyjafjallajökull," it added.

"We conclude that given the high frequency of Katla activity, an eruption in the short term is a strong possibility," the report said. "It is likely to be preceded by new earthquake activity. Presently there is no unusual seismicity under Katla."

Icelandic President Ólafur Grímsson has warned governments around Europe that a significant eruption at the volcano is close. "We [Iceland] have prepared ... it is high time for European governments and airline authorities all over Europe and the world to start planning for the eventual Katla eruption," he said.

The UCL scientists, engineers and statisticians also criticized the response to the earlier eruption."The impact of the eruption on regional airspace could have been predicted and better prepared for as the growing problem of aircraft-ash cloud encounters has been recognized for decades," the report added.

"Similarly, the potential for ash clouds, specifically from Icelandic volcanoes, to interfere with air traffic in UK, European and North Atlantic air-space was appreciated by the aviation industry well before the start of the Eyjafjallajökull eruption," it said.

"The response to the ash cloud’s arrival in UK and adjacent airspace was entirely reactive and therefore less effective than it should have been."

Don't expect a rational response anytime soon if those making decisions are politicians or people (ie. bureaucrats) controlled by politicians.

For a direct comparison, consider the risk of death or serious injury due to Carbon Monoxide poisoning. There are a number of deaths in UK every year caused by a 'combustion process' of some kind that's gone wrong (insufficient ventilation, broken flue, ..). The majority of the 10 to 20 annual deaths are caused by solid fuel burners or combustion of other than piped gas. However, a great deal on money is spent on CO awareness', fitting CO alarms which in the case of room-sealed, well-maintained appliances are almost entirely redundant, etc., a lot of it on piped-gas systems. The result is that maybe £15m is spent 'per death' on issues directly related to CO (omitting cost of training and certification of gas fitters) although it's perfectly obvious that a major part of this spend will make absolutely no difference to the annual death rate.

Politicians see votes in supporting CO Awareness, etc. but no votes in not supporting it, so that's where the money goes!

Similarly for everything involving safety issues: no benefit in reducing 'safety' and associated costs. Every political benefit from increasing it, even if from the outset it will make no difference to the safety outcome! (You will often see politicos doing their public grief acts, with a soundtrack along the lines of 'We tried and tried, and look, we increased safety budget by 50 % only last year. But sadly, despite all our efforts, Mrs Snoggins and her eleven chidlren all died in this freak accident'. It wasn't a 'freak accident', it was just 'an accident', and chances are the same result would have occurred if the budget had gone up 100%! People are dumb and screw up!

Aircraft, ATC and airlines' management of risk are highly developed and deliver excellent safety overall. However, you cannot entirely eliminate human failure and unquantifiable / unforeseeable risks such as SLD and VA. That's no excuse for pretending that zero VA is the only option, or is actually a viable option. We just need better forecasting.

Sorry Brooksie, you've got that arse-backwards. In the UK it is the bureaucrats (ie the civil service) that control the politicians. Don't doubt it!

Have you never watched "Yes Minister?" It's far closer to the truth than most people imagine.

Of course you're right about who's really in control.
However...
The bureaucrat's natural instinct is the path of least resistance leading to no comebacks.
So if one of his political 'masters' requests, for example, a safety 'improvement' which costs the bureaucrat little or nothing and can attach no blame to him later - well, of course he'll indulge the MP and give him a nice ego-boost and a few cheap votes. Someone always ends up paying and it's always Us, one way or another, never Them.

Brookes:

I'm sorry to say that until your ash forecasting becomes more accurate and operational issues regarding maintaining separation for a mass diversion are addressed, then grounding may remain the only available option.

Pace:

Please do not tell me you have not read the following report:

http://www.alpa.org/portals/alpa/vol...8AshDamage.pdf

1. There is plenty of evidence of what happens when a jet meets volcanic ash. This aircraft was fitted with CFM 56's so its reasonably representative of modern types.:


In other words, things will work just fine, right up until they don't.

That was one aircraft. You do not need to be a genius to understand what happens to engine logistics if Fifty or one hundred aircraft suffer this amount of damage, there is not enough engine overhaul capacity in the world to cope with such an event! How many times do I have to tell you this?

As for risks, of course there is risk, but the risk has to be managed. Currently the only method we have of managing the VA risk at present is to close airspace until a better method is found.

At least we can pronounce this one.

Katla is NOT erupting and there are NO indications that Katla is about to erupt.

At least, that's what the Icelandic Met Office say, and if anyone should know, they should.

Órói á stöðvum við Eyjafjallajökul (see top of page)

Re: New Scientist report on VA in engines
 

Looks like someone at New Scientist has caught the Bureaucratic Disease causing mental 'tunnel vision'. Ex Cathedra view on testing engines: 'destructive testing across a range of them will be incredibly expensive'. Yes - it would. IF you took brand-new engines straight off the line, put them in a test cell and trashed them. But that wouldn't be a valid test anyway! What you need is a tired engine that's (presumably) most vulnerable to VA ingestion, due to the crud from other sources that's already in there! So if you start your testing programme using engines that are already due for scrap or major rebuilds, cost will start to unwind. Seems obvious to me.....

And why bother taking engines off the aircraft for testing? Now we have a higher floor-limit for ash concentration (4000 microgrammes) and a max dwell time, it would be a simple matter (very low actual risk and low cost) to take empty aircraft already due for engine-removal on a short tour round Iceland, having first borescoped the engines to re-confirm starting state of the HP turbine section. OK - maybe not ultra-precise and full of exhaustive scientific perfection and rigour - but at least enough 'first principles' data to guide next research steps, if any required. Why not?

Paul is a smart man and I am quite sure he is aware of what it would take to get accurate experimental data on damage to engines from volcanic ash, especially since he did talk to the people who make and sell them. I think he is right that it would be "incredibly expensive". I imagine the manufacturers said that as well.

PBL

Given that not everyone here knows how to perform an elementary calculation of the risk due to flying through volcanic ash, I put a crude one up at http://www.abnormaldistribution.org/...cial-aviation/

It is part of what I presented in my Risk course this morning. I thought it would be cool to illustrate the things we had been talking about with a topical example.

PBL

Sunfish

You are not dragging that one up yet again as your supreme example :ugh:
I dont think there is a soul here who has not read that report half a million times.;)

That was a dense ash encounter at night who here has ever suggested that you will not get a serious problem by flying into dense ash at night?

So whats your solution close down masses of airspace for long periods of time in response to mass hysteria and and a tiny un proven risk while there are far far greater risks you are prepared to take which are proven time and time again in aviation.
Oh well Sunfish with your approach there would not be a problem as there would not be an aviation industry! Get Real :ugh:

Pace

Methinks Sunfish is anti-aviation, and hence keeps up a repetitive diatribe on mass-grounding of flights. His/her earlier stuff contains vitriolic remarks about £10 flights to IBZ, etc. Perhaps a frustrated non-pilot or eco-warrior. Certainly not a professional pilot.

Sunfish is a PPL from Melbourne who hates Qantas, hates Commercial Pilots, and thinks he knows everything about aviation.

Pity the string of crashed aeroplanes in his wake speak otherwise.

He is on a tight leash in D&G and has not worked out what the P in pprune stands for yet, but for some reason can't stay away for more than a few days. :ugh:

'Your' course? or a course you were at?

Doesn't matter - at least part of the audience must have lost focus, otherwise your comments would have been re-edited by now.

Estimating the total ticket-sale revenue for your example flight is one thing. Then using ALL of that revenue in a break-even calculation, taking into account the probability of whether the flight trashes the engines is something entirely different!

You seem to have have failed to account for OTHER costs associated with the flight, starting with the cost-of-ownership of the aircraft itself, excluding engines, crewing costs etc. OK - you dostate these are crude figures. But realities suggest that margins are already wafer-thin and it's quite surprising that airline operators at the budget end of the market even bother to get out of bed in the morning! Add on the risk of (at least 2) trashed engines during a VA alert, and it would be easy to understand a complete suspension of ops.

GROUND EVERY AIRCRAFT IN EUROPE NOW! One of our planes took a bird down an engine last night, knocking off a couple of fan blades in the process.

How long will the authorities continue to allow this madness of commercial flights when birds are flying? Can we not close European airspace?

That one bird caused 100% more damage to an aircraft than I've personally ever seen volcanic ash do!!

Professor 'L' is an authority in the field of risk management involving transportation and computer systems. I've had my differences with his analysis at times from my perspective as an operator but he has definitely influenced trends in training and accident investigation over the past couple of decades from what I can see.

I remember reading his Usenet posts years ago as he attempted more formal analysis of the human-machine interface as computers became increasingly involved in aircraft control and navigation.

Since the aircraft accident rate continues to go down, we have fewer statistics to work with so the theoretical aspects of risk management perhaps guide us more on where to allocate our training, maintenance and operational resources. Of course, politics and economics probably have the last word in the real world as many have observed on this thread.

As a pilot, I just want to keep those engines turning and not have to fill out paperwork when I land...:ok:

The calculation may be elementary, but (as ever) the devil is in the inputs.


On your item 4, you seem to have taken pCatastrophe = pIFSD - this isn't correct. Ok, you mention dead-stick landing, and lets say we accept that even with a Sully/Burkill you are still looking at a hull loss so catastrophe impact applies. Still it's not right though:

Firstly, you need all engines shutdown - and the documented incidents show asymmetric damage. Correlated, but not 100%.

Secondly, you need a failure to relight. We know that descending to clean air will cool, solidify and shatter the glass, typically allowing a relight (every time so far, I believe).

So, pCatastrophe = pIFSD * (correlationIFSD ^ no.engines) * (1 - pRelight). Couple of orders of magnitude there ?


Then on item (2) - you are probably going to have the increased inspection costs anyway as a regulatory cost of flying. Adjust your business model - or go bust.


On (3), your impact is probably going to vary much more widely. Engines have a limited life anyway, in some cases you will have effectively just lost some remaining hours use. Notably, the NASA report states that the most damaged engine was coming up for major work anyway - and it isn't clear if the 3m cost included that engine, or the work that was going to be done anyway. Conversely you could hit Sunfish's problem and have the cost of a fleet grounded due to lack of engine repair capacity. I think the impact range on (3) is more like 10^5 - 10^8 (Sunfish scenario, or bust).


But that's all minor nitpicking really. :)

Then we get to the cost of not flying.

You've used gross ticket revenue as the loss! Seriously, did no one in your audience call you on that ? [ Probably a good job I'm not on your course, I don't think I'd be a good quiet student these days :) ]

In the EU, at least, the cost of not flying is very little to do with ticket price. Much as some airline bosses would love to say "flight cancelled, here's your 50p back (less £5 admin charge)", they can't.

The main cost of not flying is the cost of getting your pax back.

Options, roughly:
1. your pax agrees to take ticket refund
2. you pay for them to get on another airline
3. you put them on one of your flights later (+hotels/meals etc. for 50% who are on return leg)

Now, (1) you'd love, but you can't choose, (2) ain't going to happen with everyone grounded, so you are stuck with (3). Cost of putting pax on your own flights - zero (more or less) if you use your spare capacity. Unfortunately, if you are running daily at say 80% load factor, a 1 day shutdown means a four day backlog (5 days total, 3 days ave pax. delay). A six day shutdown would be a 24day backlog, 30 days total, 18 days ave pax delay. At, say, 100 per day per pax for hotels (who aren't exactly going to be handing out discounts...) etc., that's 1800 per 50% of pax, or approx 150k :\ (+ some for the outward pax) for your example flight. Reality is that it may be a bit less than that because you will give seats to these pax that you would normally have sold - but those will be last minute seats that would have gone for premium prices, so you still lose several times the average ticket price paid by the stranded pax. May be cheaper than the hotels though...

And then of course if the shutdown is holiday season when your load factors are much higher than average... :eek:


Feed those numbers (150k) into your risk equation and (by day five or six) you need pMajorDamage around 1 in 5, and pIFSD about 1 in 20 (say pRelight is 0.95) to be worth not flying. Now, if you've done a few test flights looking for ash, and seen no sign of a (1) event let alone a (2) or more, I think you'd be legitimately screaming for airspace to be opened.

Same equation, even same risk events and impacts, ... very different results. All in the assumptions and inputs. [so who's right ? Well, I am not an aviation safety expert like PBL - but that isn't where we differ on our figures. Reality is that neither of us is an accountant for an airline. ]

Your regulators have done a very good job in a very short time. You should all be thankful.

And as a special favour, here is a couple of photos I just took of a scrapped first stage blade. There are well over 100 cooling channels in it, most thinner than a small needle. Many of them are not circular either.

It's about twice/ three times life size.

Pace and Brooksg will now explain how each of those little holes on each blade or vane in every affected engine is going to be cleaned and checked for volcanic glass.

Leprechauns? Little elves perhaps? The best I can think of is an alkaline cleaner, but of course I don't know what that will do to any ceramic coatings or the metallurgy, including hydrogen embrittlement etc.

http://i8.photobucket.com/albums/a16...g?t=1275178895

http://i8.photobucket.com/albums/a16...g?t=1275179465

Nice photos of a turbine blade.

So air flows through those holes and comes out the other end.

So dust is light enough to float in the air at very high altitudes and manages to flow into the cooling channels and out the other end.

Too much dust and problems begin to develop oh so slowly at first.

It's a good thing that too much of a bad thing doesn't occur very often.

Now if we could only get birds down to the size of dust specs.

It's the melting of the dust and replating that's the problem, but fortunately that's pretty rare if you manage your flight path around the worst of the clouds.

You've got it all in one paragraph there. If you talk to the sales team, who "sell" the engines, I am sure they licked their lips at the prospect of selling some additional units to a research study into the issue. "Yes, Mr Study-Leader, it is most unfortunate that what you want to study is Incredibly Expensive." Especially if it looks like a government-sponsored project, when the typical government-sponsored project approach of sales teams would apply (ie take your normal price to the commercial world and multiply by 10).