Some thoughts on aircraft damage from the Iceland volcano

There is increasing pressure on the governments in Europe to allow commercial aircraft flights to resume, because of the financial hardships they are suffering. At the same time the impact from the absence of teachers and students in classes, as they resume after the Easter break, has caused some additional problems around the UK. Unfortunately just having commercial companies take jets up and fly them around for a while, does not necessarily prove that the skies are completely safe. There is also a little discrepancy between the commercial company reports of no damage to their planes, and the damage to a Belgian F-16 plane that came back with deposits in their engines (this is separate from the Finnish F/A-18 problems). The build-up of melted ash can be seen on this borescope picture of the inside of one of the Finnish engines.

The deal that has been developed with break the airspace into three separate parts, that which remains closed, that which is restricted and that which is open, based on the conditions in different zones. The problem now will come in determining and maintaining the records of what the conditions are like along different flight paths, so that pilots and airlines can make the best judgment of how, where and if to fly. The process cannot be left to the pilots since it is very difficult to discern when the particle cloud reaches a level of intensity that can cause problems.

The melting of the ash particles so that they coat the inner parts of the engine, possibly closing off critical openings in the engine are the most common problem that a plane will apparently encounter in a brief exposure to the ash cloud. It is not, however the only problem. A 747, for example, flies at a cruising speed of 567 mph. This converts to 830 ft/sec. At these particle velocities there is an entire commercial industry out there that uses such particles, in a waterjet stream, to cut through a wide range of materials. As an illustration, this is a half-inch thick piece of titanium that one of my graduate students cut using such a system. The jet was travelling across the piece at a speed of several inches a minute, and cutting all the way through (the cut was made fairly slowly to ensure an acceptable surface finish). In steel when running a standard quality test the jet of abrasive, which carries about 0.8 lb of abrasive particles in every gallon of water, will cut to a depth of about 1.75 inches at a cutting speed of 1.5 inches/minute.

Half-inch thick titanium sheet cut through by abrasive slurry jet. (The face visible is that which was exposed by the cut).

If the impact speeds are higher, then it is not necessary to have particles in the water, though that generally requires higher impact velocities. (There is this story about Andy Fyall of the Royal Aircraft Establishment - Farnborough, a Concorde and a typhoon that I don’t seem able to find on the web! But I remember it from an early ELSI conference).

The particles that are used in cutting are quite small (they typically come out of orifices that are smaller than 0.03-inches) but they are quite densely packed in the jet, relative to those encountered in the plume of a volcano, but at high speed it does not take that many to start to do damage. Damage is reduced, however, at particle sizes below 100 microns, (0.1 mm). So the question is, how big are the ash particles? While there is not enough data yet on the current eruption particles, there is some from the eruption at Mt St Helens.

Particle size v travel distance (Sarna-Wojcicki and others, 1981)

The particles that will travel furthest appear to be mostly in the 50 micron and below range, though 100 km from the volcano there will still be 100 micron particles in the cloud that could be significantly damaging. (Respirable particles are down in the 5-micron range).

The question thus remains as to how to tell if the particles are there in sufficient density to cause problems. And so far there is not a lot of consensus it appears on how that determination will be made. The problem also arises in determining at which height the plume is going to be, since the varying intensity of the eruption has been ejecting material to different heights. More recently higher clouds have obscured the plume, on occasion, from satellite view, which is partly because the intensity is, perhaps temporarily perhaps not, decreased.

There are, unfortunately a lot more things that we don't know, as yet, about the eruption, that will only be determined with time. Thus it seems a little better to proceed with caution at this point, until the techniques for establishing what is safe, and what not, have been clearly established.

These have got to be be the most sensible words I've read since it all began:

Your article is a nice analysis by the way: to the point!


Excerpts from the Guardian editorial you link to:

We remain in a state of confusion over the threat posed by volcanic ash because the basic scientific and technical work needed to measure it more accurately has not yet been done. It has not been done in part because it has not been funded, and in part because competing scientific projects have taken precedence. There is as a result considerable uncertainty on the two fundamental questions of how to gauge more exactly the amount of volcanic material in the atmosphere, and, having gauged it, how to decide what amount aircraft can cope with and what presents a serious danger.

Manufacturers, meanwhile, will not set thresholds for their engines, presumably because they have not done the research needed to know what those thresholds are. Now that we have all had a lesson in the costs of ignorance, the necessary research will no doubt be pushed forward and the funding swiftly found. Until then the authorities will have little choice but to operate on a worst case basis.

I wonder how many other things are "out there" that we have not researched, and will eventually trip us up.

Tons of things. Most of them seemingly harmless to one degree or another, but all of them out there waiting in the wings.

For example:

How many fish can we catch before a fishery collapses to the point of no return?

How much can we dump into the world's oceans before we create to many dead zones?

What will happen to all those tiny particles of plastics that are in the ocean, with more big ones getting smaller everyday?

What is the rate at which we can cut down trees before we tip ourselves into world wide deserts?

How many parts per million of CO2 can the atmosphere hold and allow humans to still live on earth?

How many species can die off before humans can't live in the environment left?

What happens when all the bees die off?

How many people can work for the gov't before there is no one left to do anything else?

The list goes on and on.

CEOjr - excellent questions - in fact by your list you point out that there are plenty of known things out there that might trip us up, but we just don't want to look at them because to deal with them might hurt our way of life or some company's bottom line.
What we really fail to appreciate is how all those things connect to other things.

Did anyone think that a volcanic eruption in Iceland would affect fruit and flower farmers in Kenya.

When Kenneth Maundu, general manager for Sunripe produce exporters, first heard about a volcano erupting in Iceland, he was excited. “I thought, ‘Oh, wow, a volcano,’ ” he said. And then reality hit him in the face like a hurled tomato. Because Kenya’s gourmet vegetable and cut-flower industry exports mainly to Europe, and because the cloud of volcanic ash has grounded flights to much of northern Europe since Thursday, its horticultural business has been waylaid as never before.

The connections are by and large unknown unknowns. What a fragile web we have woven....

Lots of things that we don't know about.

The most fundamental aspect of the volcanic ash is the size distribution of the particles and I am not sure if anyone knows what this is. I think they can get it indirectly through microwave radar scattering cross-sections:

If it is anything like aerosols, you will find likely a power-law distribution of particle sizes, with lots of very little ones and progressively less larger ones.

Power law distributions usually come about by a simple explanation which I just posted on:

Gail said:

I wonder how many other things are "out there" that we have not researched, and will eventually trip us up.

That is what I find challenging. I tend to post a lot of my individual bits of research on TOD and I realize that many people get annoyed by my persistence. Yet many of the topics have simple explanations, you just need some motivated researchers and somebody that will listen. Scale this up to a wider more general audience willing to listen, and there you go.

Cool little blog article you posted, good to see you smile a little ?- )

Concorde, Space Shuttle ... if someone proposed to build those today, they would laughed out for lacking proper safety features, risk assessments, testing and further testing at each stage. We forgotten our sense of proportion and common sense when it comes to engineering safety and tolerances. There needs to be a quantifiable and finite risk involved in everything. Insisting in zero risk will lead to infinite costs where as what you want to achieve might actually be worth the risk: space exploration, global air freight, commercial passenger travel.

I bet if it was 20 years ago, without the benefit of accurate satellite surveillance and laser tracking we would be oblivious to the risk - some airspace would have e been closed in the vicinity of the volcano - probably based on pilot reports - and airliners would simply be directed to fly past the visible dust cloud. This is after all the its been done in the past around the world. The few aircraft that have experienced malfunction due to volcanic dust have been flying at the immediate vicinity of the volcano and its thick visible dust column - not 1000 miles away or more as is now the case in most of Europe.

Why this paranoia? Well, its the uncertainty - the unknown - nobody knows what is the treshold of concentration and particle size for volcanic dust which will cause a unacceptable increase in risk of engine failure. Past experience be damned - we need data. Hard evidence. Meanwhile global economy suffers greatly from this overreaction.

Overreaction I say because the test flight performed by the airlines have shown that tou can fly over Europe for long distances, while being exposed to the relatively small concentration and surely miniscule particle sizes of these so-called dust clouds. Perhaps the all the heavier damaging particles have already dropped down into the North Sea by the time they reach Europe? Who knows.

Now the military jet engine damage reported by FAF might not be relevant: lets examine it 1. these aircraft were being flown in north of Finland - a lot closer to Island then most of Europe. 2. The 'damage' to the engine was indeed serious - requiring overhaul level maintenance to the combustion chamber to remove the deposits - however we do not have the data if the engine performance was effected in any way - at least apparently noticed no difference and the dust was only discoved by inspection on the ground. The jet engines in military fighters are different in that there is alot less bypass air - and thus almost all particles going into the air intake do go throught the core of the engine. The engines are designed and rated rather differently to commercial airliner engines in that they have a more frequent maintenance cycle - perhaps a modern commercial airline jet engine could widthstand a lot more abuse as its been designed to be flown non-stop without maintenance for very long periods.

Anyway this is all idle speculation until someone has the courage to start the flights again - as seems to be case in now. The world is too dependent on air travel and cargo - the risk is worth it - and doing it by common sense, mitigating the risk: boroscope inspections of engines after each flight - careful monitoring of engine performance values - these will begin to give a basis for some scientific data on where the threshold might be.

Ransu, stuck in Hiroshima

Neither the Concorde or the Space Shuttle should have been built.


Shuttle was/is military/weapons-research driven, justified by the usual blather to dominate the world.
Civilian benefits were/are the Public Relations to get taxpayer money to do it.

It really is too bad Hubble is giving us all those pictures?- ) Sure the shuttle wasn't the most efficient use of resources, but put it in the context of the nuclear arms race going on at the time...was it better to build and run the shuttle or build and arm and operate a thousand more silos and ten more nuke subs. I exagerate but those were some of the dollars the shuttle program was competing against. The shuttle did help a great many people get a much better feel for just how little a marble we all live on. More nuke subs and silos actually make the marble smaller, but since they are basically invisible they don't help most people see it in that way.

No doubt weapons money is wasteful in the extreme but I don't see that sort of thing going away. The shuttle has had far more positive impact than any other weapons work I can think of, except for one type--the one which has led us down the road toward both the most terrible and positive possible of outcomes.

An improved and simplified Saturn type system would have been safer and cost less IMHO.


You could well be right. Hope what we learned building and operating the shuttle instead will end up being worth some of the costs.

I recall reading long ago an opinion piece that claimed that NASA management instructed the designers of Hubble to design-in the need for periodic maintenance. because they needed justifications for the Shuttle, while the Space Station was being built, very slowly.

Hubble could have been done a different way. Maybe with more attention to detail on mirror/corrector plate figure.

As to military spending wasting money --- Suppose all that money had been spent on better diets for people throughout the world. Then we would now be in even greater overshoot. Would that be a good thing? I wonder.

That's water long under the bridge, and likely very muddy water at that. Some of the tech they have been able to add wasn't even on the drawing board when the Hubble was first launched. Care to use the computer you were using way back then then? One of the big advantages to proposed solar wings doing some of the work now done by satellites is that the wings won't have real long lives so the tech can be upgraded on a continuous basis.

Interesting thought, overshoot vs. military spending, quite the can of worms, especially if sixty odd years without a major world conflict gets factored in, truly a squiggly mass to try and get a mind around. Just from a selfish point of view I am glad it has coincided with my sixty odd's hoping it works out well enough.

For an answer to your mostly misinformed rambling, see the guardian article I posted a link to above.


Concorde, Space Shuttle ... if someone proposed to build those today, they would laughed out for lacking proper safety features, risk assessments, testing and further testing at each stage. We forgotten our sense of proportion and common sense when it comes to engineering safety and tolerances.

I found that I had to fight very hard against my desire to unleash a long stream of expletives upon reading that!

You may want to read Richard Feynman's report on the Challenger disaster.

His concluding words were:

For a successful technology, reality must take precedence over
public relations, for nature cannot be fooled.

For whatever explanations they had for the first disaster, that case was never closed. I don't care what Feynman said.

The alternate explanation was a huge amount of torque on the launch platform. The asymmetry of the launch configuration contributed to a huge shear force that damaged the shuttle as it lifted off. The theory at the time was that this would have happened independent of the o-ring's condition.

BTW, the launch configuration geometry was changed thereafter.

I like to bring this up because that was what the engineering magazines were talking about at the time.

"....The jet engines in military fighters are different in that there is alot less bypass air - and thus almost all particles going into the air intake do go through the core of the engine."

Above statement has no bearing on how ash particles will affect jet engines.

Commercial engines will be affected by the particles in exactly the same manner as the military engines. The compressor section of the engine still must function as the mechanism to increase pressure of the intake gas in both military and commercial jets. The difference lies in the commerical jet using some of the power produced by the turbine (expansion portion of Brayton cycle engine) to drive a ducted fan, somewhat like a turbo prop engine.

If volcanic particals reduce the performance of either the compressor or turbine in a jet engine, the power will be reduced, whether it be in the form of exhaust gas velocity or air velocity through a ducted fan. Because the power produce by the jet engine is measured in mass times velocity of gas exiting the engine, this applies equally to both military and commercial engines.

I spent nearly five years working on military aircraft for Boeing predecessor.

One of our colleagues has been stranded. He was originally supposed to fly back from the UK (where he is from originally) to Philadelphia on Saturday. His earliest flight now is scheduled to leave the UK on Friday. Too bad. He doesn't have any choice but to blow away a whole extra week of vacation time. I hope he can make good use of the time.

He can't settle down with a laptop and an Internet connection and get some viable work one? I'd never make my guys eat their vacation unless they actually planned to spend the time playing.

Many years ago, a British Airways Boeing 747 actually flew through volcanic ash, and all 4 engines shut down for several terrifying minutes. The plane started falling out of the sky and seemed fated to crash into the ocean. But when it descended to a lower altitude where the ash cloud dissipated and the air was clearer, the pilots managed to get the engines started again.

The whole story was made into a documentary for the Air Crash Investigation/Mayday series on National Geographic:

The issue with volcanic ash is not only the density of the ash cloud, but also that the granules of ash are extremely coarse and corrosive. When they inspected the airplane after it landed, the leading edges of the airplane wings and the nose looked like they had received a heavy duty sand-blasting. The engines were clogged with ash, and in some areas of the turbine shaft, the ash had actually fused with the metal. All 4 engines had to be replaced.

I flew for small airlines off and on for twenty years. It used to be an excellent job, but began to decline in the late 70's, due to deregulation and financial pressures, etc. The same has happened in the larger aircraft airline industry. When the weather was bad (Yukon) and passengers began to get restive, I would tell them I would take a look but they would have to pay for the aircraft time in the air if I had to turn back. Not once did they ever take me up on it. Sometimes, my employer would ask me to take a look. Sometimes, I did it on my own out of boredom.

The point is, as the economics of the industry declined, and the expectations of the public increased, the business became increasingly unsafe and poor, although it would be denied by all who are still a part of it. If you were unionized, you had backup, but the race for the bottom continues to manifest itself in all segments.

The airlines are fighting for their lives, and those of us on TOD know that this is one wrinkle in the process that may speed things up.

Paying for hotel rooms for passengers who are stuck somewhere is an impossible expectation to fulfill. There is no free lunch. Only the flying public as a whole will pay for those rooms, or they will be paid with bankruptcy by the airlines society has come to depend on.

Glad I am at home baking bread.

That "race to the bottom" comment struck me in a double whammy.

First, I don't know if "race to the bottom" was meant to have a double meaning - it would be tragic for a plane to race to the bottom because airline financial needs forced pilots to fly in unsafe conditions.

The second thought from "race to the bottom" relates to my work as a design verification engineer - I (and my team) ensures the design is correct. However, design complexity keeps increasing at a furious pace at the same time as the number of people to verify designs has been reduced through cost cutting measures. Although we continually strive to improve our verification processes over time, at some point the increasing design complexity exceeds the capability to match pace in verification process because the permutations exceed the the number of people and processes than can be developed to test the permutations. (That is of course assuming "real world" of working a constrained environment of having to stay on schedule and with limited team of people.) Thus I see increasing reliance on risk evaluations (do we need to test this feature or that feature) that will lead to decreasing quality of products. And when you think about the quality of products, in general, there is, in my opinion, a race to the bottom. Go to any toy store and look at the dregs they sell there. (American auto quality has improved since the '80s though.)

I wonder if there's could be a measurement of perceived quality of goods and if it would by strange coincidence match Hubbert's curve of energy availability. (Would the quality curve be a leading or lagging indicator?) (I withdrew from probability and statistics - I kept falling asleep and it wasn't a prerequisite for graduation....)

I wonder if there's could be a measurement of perceived quality of goods and if it would by strange coincidence match Hubbert's curve of energy availability.

I'd be willing to bet significantly that there has been no "decline curve in quality". People are notoriously poor at perceiving reality in this type of issue. I think back to eg. 1970's when it pretty much required a personal mechanic to own a car with fuel injection, or when car steering wheel columns would simply spear the driver in an accident. You can still buy good quality hand tools if you're willing to pay the price (eg. Klein lineman pliers are still identical to what they used to make). What specific product quality do you refer to?

'Wooden' Furniture

Cigarette Lighters

Mechanical Pencils

Storm Door Latches

Broadcast News

Tent Nylon

I agree that you CAN still find quality items, but I don't think that the preponderance of generic products have been heading higher as well.. a great many manufacturers are on a constant quest to economize.. and sometimes it's an improvement, but often enough, it means cheaper materials, faster assembly, and of course more pronounced 'Obsolescence Planning'.

(kind of combined comment here)

I did state that since the 80's autos have improved. Intuitively, this is a case of people seeing that the German/Japanese car was just put together better than the U.S. cars of the time. When U.S. manufacturers started loosing enough market share, they started improving quality. There are likely other areas where people started talking with their wallets engendering a quality improvement response.

On the excellent JK list - this is an example of the several areas where IMO quality has suffered. I enjoy making wood furniture as a hobby, and I recognize quality when I see it. When I go shopping for furniture (I don't have time to make it all...) I embarrass my wife by crawling under the tables and pulling out the drawers and otherwise inspecting the build - and what I find is that there are an incredible number of expense saving shortcuts built into what is even "high-end" furniture at expensive stores like Haverty's. Even joints like dovetails, the hallmark of a well built drawer, are sloppy and poorly executed. Craftsmanship is missing - and in fact, it's a damning statement that craftsmanship has been sacrificed on the altar of cheap for most construction/manufacturing/building. Yes, there are still small pockets of people who love creating with their hands, but most people buy at Walmart...

BTW - Let's add "Coach Class Flight Experience" to the list of declining quality...

Now let's look at another aspect - I would buy better quality items at marginally higher prices - the problem is, I'm finding it hard to find better quality at marginally higher prices. For example - my wife and I wanted to replace our family room lamps. So we went shopping for lamps. We went to four specialty lamp stores, and two "big box" stores. In three of the specialty stores, and the two "big-box" stores, you could have inter-mixed the products and prices and have been in the same store. They were almost identically built (mostly in China) with minor flourishes in style and prices ranging from $30-$200. Only one specialty store had very different and reasonably artistic lamps, but the premium price was more than I was willing to pay for a lamp. There the prices started @ $600 and up. So my range of choices were, lots of cheap poor quality products - extremely available, and a (hard to find) select few higher quality products at a significant premium.

This quality/availability issue is something I've found in shopping for a number of things - furniture, toys, clothes, and sporting goods. There's a flood of really cheap doo-doo out there. Quality is hard to find and the premium for that quality is astonishing.

Well there is the issue of where time is spent, entertaining guests in a well appointed salon, reading in an imposing wood paneled study or staring, typing and clicking at the ever improving LED or LCD screens, so all comparisons with the past are fraught with difficulties. I do love seeing a fine piece of wood furniture though, but cost benefit analysis has kept me out of the Treeforms store for now.

JG, That is actually a pretty brilliant premise that you have posed.

Any Hubbert-like curve has an accelerating component. I have always said that the decline sets in when the accelerating component starts to hit the ceiling of a distribution of volumes, not as people tend to classically describe as a negative feedback on some fixed volume. Your permutations are like a dispersion of searches and the complexity of designs are like a range of ceilings.

I will definitely try to see if I can formulate this in terms of probability. Like I said, it's a brilliant premise, and that's all the motivation I need. Stay tuned.

I never realized I could submit a premise in my ramblings, much less a brilliant one. I'm glad to offer fodder for this forum's musings. If, in your formulation of probability of this premise you can show that laying off my people while increasing complexity causes a reduction in quality - maybe I can take it as ammo to my bosses to hire again! The cost for quality escapes caught by customers is enormous compared to catching them in design.

I am in productivity studies up to my eyeballs.
see this

Given the irregular dispersion of this ash cloud, how will we know about the varying concentrations of ash in the atmosphere? When boarding a plane will we be sure it wasn't damaged in one of the previous flights?

We also get a foretaste how pushy the air industry will be when kerosene supplies become scarce and what impact that will have on the economy.

Airlines have again been weakened, reducing their chances to survive the next oil price shock.

This graph shows the loss in demand for jet fuel

From this article:

"JBC Energy, meanwhile, reminded clients on Tuesday that there were also consequences associated with there being too much jet fuel in the supply chain — especially in an environment where it was still economic for refineries to process the product.

That resulted in a hugely steep, if temporary, jet fuel contango — currently encouraging tonnes of jet fuel to head into floating storage. Traders make money out from this by buying the physical product now, and hedging the sale in the future when prices are higher."

Some thoughts here too:

Comparing waterjet cutting to volcanic particles encountered in flight isn't so useful. First of all passenger airliner air velocity is limited to about 0.95 mach true airspeed as well as possibly fuel economy considerations. So the normal cruising airspeed for a 747 at 30,000 feet is a bit less, about 520 mph which more like 700 fps.

Secondly the particles encountered by the body, wing edges and turbine fan leading edges first hit a graduated pressure wave which tends to direct airflow around the surface in a so-called laminar flow. Any body designed for flight has been formed thus to reduce friction from air, but more importantly, to maintain a laminar flow around the object (laminar as opposed to turbulent). In laymans terms the air first hitting the body slows down and forms a kind of cushion directing further air around the body (when we go above mach one it gets more complicated). So particles in air would have to be heavy enough to not be effected by this pressure gradient trying to push them aside from the surface. Any effect on them would change their velocity vector away from the perpendicular to surface of the body and thus any impact will be a lot less effective. A more interesting comparison would be one from military target ballistics for inertial munitions - they're effect on impact can be almost completely nullified by changing the angle they strike.

Now someone with more time on their hands right now could dig up some actual wind tunnel test results for particle impact effect for wing leading edges (there should be plenty of research around on this). All I can tell you from my experience with aircraft is flying in a dust storm - with actual grains of sand with particle sizes from 1000 microns to 1 mm. Of course in a private plane the airspeeds were a lot less but then the particles were huge in their mass compared to volcanic dust. Anyway couple of kilometers of dust cloud did manage to start 'sanding off' the hard surface of the paintwork - making it look matte instead of glossy as it was before. This might cause a slight increase in forward friction but no loss of laminar flow yet at those speeds. A much more dangerous effect was the accumulation of sand in the air intake of the engine - despite a particle trap in the intake designed to 'throw away' particles from the airflow entering the engine. Consequently particles did enter the cylinders and could even be found in the oil filter afterwards.

Now a jet engine is a whole different ball game because its all about airflow. Lets follow a course though a typical commercial jet engine - so-called turbofan engine (high-bypass type). As the particles approach the engine, the air they are suspended in is cut into very nice laminar flow slices by the huge fan at the front of the engine. This fan produces most of the thrust of the engine by 'throwing air backwards'. The air hitting the leading edges for the fan blades is quite fast so the blades are angled much like the aircraft wing and any particle would probably be tossed aside. Most of this air actually goes past the actual engine via the by-pass duct.

However the engine does need some air to combust its fuel so some of the air is sucked into core of the engine where it encounters the compressor stages. What the compressor does is actually slow down the air in order to compress it. You need to compress it because air density up there is so scarce that you need to bunch up a lot of it to even light a match. The compressor has multiple stages - every stage having a different blade angle which operates at a specified airspeed range.

Ones the air is compressed though over a dozen such stages it will have slowed down a lot. Now comes the magic. The air is mixed fuel in a combustion chamber - a kind of multi-layered 'bottle' were the hot flame is held by a surrounding air cushion in the middle of the chamber.

Before this the compressor has bled compressed but still relatively cool air by tiny air bleeding canals all over the engine. This bleed air keeps the engine parts cool and these canals are the ones vulnerable to clogging by particles. Now the bleed air canals in the combustion chamber are critical - they keep the metal from being melted by the flame in the middle - not to mention overheating which changes the metallurgy which can lead to bending and shattering of moving parts. You can imagine the more hot the part has to operate the more cooling air and thus bleed canals it needs.

Now the flame hits the turbine blades - these are the ones actually doing the work - being now pushed by the hot airflow instead of sucking it. These blades are specially made and delicate structures - almost void from the inside like Swiss cheese to allow for maximum cooling air flow inside each tiny blade - but just enough structural strenght not to them shatter to pieces. And they will, if they overheat!

But we have missed yet another effect other than the clogging of cooling air canals. There's also deposits. As I mentioned the tiny blades in the turbine are just so made to withstand under extreme conditions. If however their surface starts deforming from accumulation of melted volcanic dust deposits they will become unstable, unbalanced, causing excessive accelerating forces on them which will quickly shatter them. So too will the deforming of the surface cause the airflow to become turbulent and thus further increasing such damaging forces as well effecting the airflow into the next stages of the turbine.

This is the reason for the maintenance overhaul the engines need to periodically go through - complete disassembly - dissolving of any deposits by strong chemicals - and then building up their protective surfaces for exactly right form and mass using exotic means such as particle deposition chambers.

Disclaimer - this has been written in bed on fever somewhere in Hiroshima ... stuck here as everyone else - hopefully can go home to Finland next week...

- Ransu

"... So particles in air would have to be heavy enough to not be effected by this pressure gradient trying to push them aside from the surface. Any effect on them would change their velocity vector away from the perpendicular to surface of the body and thus any impact will be a lot less effective."

Being an engineer that has some training in fluid mechanics, I say you are wrong.

How do you think modern centrifugal air cleaners work to extract particles as small as a few microns?

The particles do not follow the air flow but continue on a straight path as the air molecules travel on a rotational path, same as would be for air flow over the curved leading edge of a wind turbine blade or past a compressor blade in a jet engine.

I work at a dockside where we export very dusty iron ore to China.

I have been arguing for centrifugal air cleaners for some time.
Where can I get more information on them?

Jeff Masters writes briefly about the computer models that are being used to forecast ash concentrations, and the uncertainties in the data that is fed into those models.

Commenters at Marginal Revolution raise a number of interesting questions about airline motivations. For example, an airline that leases its planes, with maintenance costs borne by the actual owner, has less incentive to avoid conditions that would shorten engine life.

Commenters at Marginal Revolution raise a number of interesting questions about airline motivations. For example, an airline that leases its planes, with maintenance costs borne by the actual owner, has less incentive to avoid conditions that would shorten engine life.


There might be zero risk of an ash-induced crash ... but why would a discount airline which makes say $10000 per flight want to risk a $100,000 engine rebuild cost?

but why would a discount airline which makes say $10000 per flight want to risk a $100,000 engine rebuild cost?

It's quite simple really. The airlines were going to go bankrupt if they did not start flying again soon. Now if they fly and trash their engines they may still go bankrupt but at least they went down trying. If they don't trash their engines, then they survive.

Not necessarily true. British Airways was the most affected airline, losing upto $10m a day. They have an operating profit of around $400m a year - the impact of even two-three weeks of complete cancelations would have eaten into their profit for this year, but wouldn't have threatened bankrupcy unless it continued for months.

Most financial analysts agree that the recent strike action has done more to damage the company than the volcano.

Most financial analysts agree that the recent strike action has done more to damage the company than the volcano.

When a firm, or a person, has multiple choises as to where to place the blame, you can count on firm/person to blame their enemy rather than mere bad luck with Mother Nature.

Heading Out, Just awesome work! Great info.

What a mess.
I think Reykjavik airport is open. You fly up there from the US and take a 3 day boat trip back to the UK.
The UK should send an aircraft carrier and a couple of troop transports up there.

This another good collection of volcano photos. A lot of these also show the effects of the ash on humans and animals.

I'm not familiar with the specifics of the dust clouds, but I can provide some perspective of the metals involved. I agree that wear/erosion damage caused by solid particles at high speeds is an issue, particularly for the airframe components made from aluminum. The clogging of cooling ducts is another serious concern within the engine.

In modern jet engines, the combustion temperatures can approach and sometimes even EXCEED the melting temperature of the nickel-based superalloys used in the engine. Only through sophisticated cooling channels (which might be prone to clogging) and protective and insulating surface oxides layers on the outer parts of the turbine blades does the interior metal stay cool enough to handle the stresses of the engine.
My biggest concern would be the high sulphur content (I don't know the details of this vocanic ash but suspect it's a lot higher than just from jet fuel). Nickel superalloys designed for coal-fired powerplants have significant differences in alloy composition to withstand the effects of akali sulfates in coal, as compared with the alloys used for jet engines. The problems would manifest as breaches in the protective oxide layers, and would destroy the engine fast, potentially brazing parts together, as described above.

What an amazing group of contributors. Heading Out, Jim, marco ransu and the rest of you have been clear, informed, sensible and everything we have not been getting from most of the MSM - the Guardian is an honourable exception. TOD and its contributors have earned my gratitude many times in the past. Thanks again to everyone.

True. But the WSJ (4/20,A10), believe it or not, has a few good articles on this topic, at least one of which discusses some of the points raised by HO. Maybe someone can grab a link.

Just announced - UK airspace to fully re-open at 10pm UK time. BA flights heading to UK airports now.

Situation will be kept under review depending on location of ash cloud.


Airline Review

Latest Volcanic Ash related aircraft incidents ?

By Miyuru ( K FLYER ) on April 21, 2010

Following incidents have been reported after the re-opening of UK airspace last night and are currently believed to have been caused by volcanic ash. But please note that these events are *still* under investigation.

A World Airways Boeing MD-11, operating for Allied Air, that flew from Benghazi, Libya to Ostend-Bruges, Belgium via Maastrichat ( on 20th ) was grounded due to ash found in engines. The engine reportedly suffered non-serious damage. The aircraft is currently being inspected.
The aircraft in question is N384WA. Allied Air is a Nigerian operator.

A Thomas Cook 757, reg G-JMCF, on a positioning flight as TCX952P, returned to Manchester due to a loss of compressor bleed air from one engine after crew sensed an ‘intense smell of volcanic ash’ during the climb between FL160-FL200. The aircraft was out over the North Sea off Norfolk/Suffolk.

The live ATC recording of the Thomas Cook incident could be found here.

Legal Disclaimer : This recording was not done by this author and was found at another aviation forum online. This is posted in this blog in good faith solely with the intention of keeping readers informed. No airline or airport or any employee was meant to be harmed. If any involved party believes that this is in violation of legal regulations or that it harms them, please contact me and I will remove this right away.

The concentration of particles and oxygen depleted gasses required to shutdown jet engines is vastly higher than the concentration of particulates that will do damage to an aircraft that will cost more than the profit on ticket sales. It is to the airlines advantage to avoid flying through air contaminated to the lower threshold.

News stories imply that the only options are BAU or NO FLY, but there is middle ground. Aircraft could be allowed to fly near the contaminated air masses in daylight visual conditions where pilots could maintain visual separation from contaminated air. Capacity would be reduced, but stranded passengers would be able to return home in safety.

An interesting blog that is no doubt getting far greater readership is Eruptions "Your host is Dr. Erik Klemetti, a geologist who spends most of his professional time thinking about magma. "

Quote of the day from another excellent blog - Effect Measure

As an aviation expert on one of the TV networks commented, "It's much better to be on the ground wishing you were in the air, then in the air wishing you were on the ground."

First flight finally lands in London, from Vancouver, after over 10 hour flight.

Link to BBC story, "First plane to land at Heathrow since last Thursday"


The thought that's been occurring to me over this is:

The primary problem is the ability to know where the dense clouds of ash, etc. are actually located, in real time. The models are OK, but as you promulgate in time the accuracy becomes less so that by the time you get to Europe, its little more than a rough guess. With the risk averse culture, that equals closed airspace.

However, for the particulates concerned, you ought to be able to detect them with backscatter. With the sun shining down and the right optical setup you should be able to make a direct measurement of the density at particular particulate size, from satellite. Now I'll bet nobody has designed and flown such a system yet, but the turnaround on something that could be put in the shuttle shouldn't be too long, for a low earth orbit device.

Isn't this a case where there should be a rush job to get something up and running - particularly if you don't know how long its going to last?

I'd suggest what this shows above all is the peril of putting arts grads and accountants in charge. Wrong people for the job, particularly when you start thinking of the realities of a post peak world where this time of SNAFU will be a regular occurrence. We need people who can really work the problem, with an understanding of the big picture.

They are already using backscattering with lasers from the ground to measure this, but you are right that a satellite would give much better regional coverage. The ground based units just can't measure that much sky at a time.

The problem with LIDAR in general is that it doesn't have very good cross-range; you can point a LIDAR on the ground straight up, or a LIDAR on a satellite straight down, but if you try to point it very much off vertical the data quality gets unusably worse because of scattering in the longer lengths of air.

So you get a very nice one-dimensional profile of the atmosphere above your LIDAR station, but you *can't* do a radar-like scan and get a profile out to the edge of space and to the horizon. Unless you can make LIDAR stations cheap enough to stick one in each grid square, which is not easy because they need decidedly bright lasers, you can't use them for regional coverage of the sort you want.

There is at least one satellite up with a cloud-sensing radar on it, and you see something that looks a bit like the plume at the left-most edge of chunk 26 of (click on the purple '26' on the image), but you can also see that that's producing profiles of the atmosphere straight down along its track - it look me a little while to find a pass where the track intersected the ash.

Cloudsat's radar is quite a powerful instrument - the radar pulses are 1.8 kilowatts at 94GHz, enough that it required special dispensation from the people who handle frequency allocations worldwide, and that radio-telescope operators have to take care not to point at it during an overflight because it would actually burn out the receivers.

There's a LIDAR satellite up as well, you can see profiles at URLs like but again the plume isn't exactly shouting out - the satellite is rather more intended to survey tropical thunderstorms.

I suspected this, thanks for the more concrete explanation and the links.

Another cautionary note about LIDAR. Clouds are spherical water droplets. Volcanic ash is irregularly shaped solid. The backscatter of these different types of particles might be very different. I'm sure the appropriate authorities have very good information on the backscatter cross-sections for cloud particle, and some information on backscatter by crystaline water ice, but volcanic ash --- not so much.

So build solar powered airships.
Or not.
You humans exasperate me.

OK. Time to use your huge brains to rationalise your stupidity.

A good friend of mine pointed out to me the reason why even solar powered airships are not economical right now:

Transit time and personnel. You need to pay more labor cost per passenger mile and until energy costs go up a lot the current jetliner model is more cost effective.

Ask your friend if he modeled his costs on recycled PET and whether he used solar concentration.
Did he use a combination of hydrogen and steam for static lift?
What regulatory environment did he assume?
Did he assume that the pressure of time would be factor in future economics?
Did he assume that burning carbon would not be a capital offense in future?

What were his assumptions?

Very simple assumptions:
More time in the air=more in-flight support personnel hours.

If the flight time is too great you need additional crew members to allow shift rotation, as well.

People are still expensive compared to fuel. If that changes for either market or regulatory reasons then solar LTA travel becomes more practical.

Until it changes, however, there is no reason for any business to invest in it.

Oh Oh...

Offshore helicopters report volcano ash flight problems

Helicopter flights over the North Sea were recalled after two aircraft reported being covered with volcanic ash.

The two Bond-operated aircraft were flying about 70 miles off Aberdeen.

The pilots reported ash on the windscreens after flying through a rain cloud on Tuesday night. There was no damage and no ash was found in engines.

For the right brain.

From APOD April 19.

As for the velocities entering the engine, the ram effect would occur only at the first stage of the compressor. The velocities at the last stage of the compressor would be low since the compressor packs the air against the combustor. Compressors change the velocity head to a pressure head. Velocities increase as the fuel is burned in the combustor and exit the wheels of the power turbine. These turbines spin at around say 20000 rpm and I doubt for the time the plane is in the cloud silicone would have time to deposit on the wheel of the power turbine. However, if this did occur and serious vibration did occur, the engine is designed to fall from the wing. The transatlantic fights are designed to fly with one engine. FAA rule. Even the 737’s will fly with one engine.

I believe the reason for grounding the planes is to avoid collisions with other aircraft in flight. To conserve fuel, the altitudes that planes fly were lowered. With the large number of fights in the air, crowding between planes has become a problem. If the planes flew through a cloud of ash, the engines would stall on some of the planes. This would force some of them to glide. With limited control of a gliding aircraft, this would pose a serious danger since they would not be able to fly in their proper lanes. Turbofan engines have a sparker in the combustor that runs continually. This is a safety feature. The engines would start as they exit the cloud because the rotors are still turning and the spark will ignite the fuel.

Another thing is that the radar which these sophisticated aircraft use to maintain proper station would not perform properly, as in a fog. The radar also instigates the warning system for the pilot so that a collision can be avoided. Cruising along at 600 mph does allow the pilot by sight to react if another plane is on a decreasing range and constant bearing. Radar is vital.

The impact of the ash occurs on the first stage of the compressor. Modern turbofan engines are designed to run with a limited number of blades missing. The modern turbofan is very rugged. I believe that most of the garbage could be passed through the engine.

Another thing I forgot to mention is cabin air usually is taken off of one of the stages of the compressor. So going through a cloud of ash would pump tainted air into the cabin.

By way of an anecdote, I've just managed to get back to the north UK from Tenerife (Canary Islands, 3100km trip) after being stuck for 5 days. UK airspace is now open. I didn't notice anything amiss up to 38,000 ft! But the sunsets over the UK have been a nice orangy colour apparently.

What struck me though is how rapidly things start to deteriorate when things go amiss. We were reduced to washing socks in hotel sinks and totting up our available funds to see what we could afford to do. The holiday insurance was as useful as a chocolate fireguard - most of the important cover was voided due to the volcano being 'an act of god'. Etc.

We were reduced to washing socks in hotel sinks and totting up our available funds to see what we could afford to do.

And here I was, thinking that's pretty much BAU... Silly me! ;-)