lomapaseo
Not so. No cooling effect doing it your way. Cool air is taken through a bleed and exits from all the holes in the blade, thus keeping it cooler. The dust travels through the bleed system and can melt and block the exit holes... blade gets too hot and is damaged.

This is the key to the whole set of issues around engine damage caused by LOW levels of VA.

(Forget, for a moment, accurate detection of areas of HIGH VA concentration in bad visibility and especially at night, and the specific risks from this. Forget also the possibility of blocked pitot heads and other critical features of the aircraft that might be affected by LOW VA .)

A VA particle passing through a combustion chamber will probably be melted, so may solidify onto a turbine blade. Yup - Very Bad Thing, especially if the build-up of glassy material blocks the exit(s) of cooling duct(s).

VA particles going through the cooling bleed and then through the inside of a (hot) blade might also melt and would then presumably be more likely to re-solidify in a clump where the temperature was lower and block some ducts. Another Very Bad Thing.

BUT what is the temperature of the cooling air inside a blade or other potential hot-spot? As low as possible, obviously, so as to give maximum cooling effect - engine manufacturers have a design trade-off between larger volume of hotter air versus smaller, cooler volume to achieve a given cooling effect. So given that it costs thrust to divert air into the cooling bleeds, the air temperature is going to be minimised by design. The big question: can the turbine cooling air temperature ever exceed the melting point of VA? If so, under what circumstances and where?

Anyone know this? I don't know and can't find any reference myself....

No doubt the answer will probably be yes, if
But it hasn't happened yet because the probability of the if factor and a high ash concentration hasn't come together.

I wonder if the if factor includes a meteorite strike at the same time

My thanks to Airbubba for his encomium. I hope I deserve it!

This one.

Concerning my crude PRA, both brooksjg and infrequentflyer789 point out that identifying revenue with net income isn't realistic. I know that, indeed I thought I had pointed it out.

Do they have a better one which can be justified using publically-available figures?

My trivial calculation yields a low estimate for the risk; in other words, if you think net income is less than this revenue estimate, which it almost certainly is, then my crude estimate of risk is an underestimate. It still seems to me pretty high, rather higher indeed than Pace's estimate of zero risk. That's why I said it yields insight, because many discussants seem not yet to have seriously attempted to estimate the risk.

Infrequentflyer789 apparently wants to add another term:
Is it?

On the first day of the ban, I was in Delft, in the Netherlands, with people who had travelled from Vienna, Suffolk and Liverpool, all busy trying to rebook themselves by rail. None of those people have been permanently lost to their carrier of choice that day. As far as I know, Eurostar has not had a noticeable permanent slump in bookings since the debacle in mid-December 2009. And I doubt all those transatlantic passengers are going to start travelling by ship. (I do know of one set of colleagues who travelled back to Brunswick from Beijing on the Trans-Siberian railway! But they didn't all do it; my colleagues who took a chance on waiting for the next available flight managed to get back a few days earlier.)

So I am not sure about a claim that it is the main cost. But if you have a way of including some estimate of it in a risk analysis, please go ahead.

You also want to say that the severity of losing all engines is not necessarily catastrophic. Sure, as anyone who read about the Air Transat "save" of August 2001 knows, but it is usually taken to be catastrophic as far as certification and regulation goes. Some - indeed some would argue most - engineering definitions of risk classify an event category by worst-case outcome.

I am not sure what equation you mean – I didn't propose one.

I don't see off-hand how «feed[ing] those numbers» in to anything I wrote will give me something which I can interpret as a risk estimate, but as I said if you can indeed produce a modified risk analysis with it according to the De Moivre formula, and you can justify the approximations, more power to you. I'd like to see it.

PBL

PBL

Where please have I indicated that there is Zero risk?

When you get up in the morning and cross the street there is not Zero risk that you will not be flattened by an out of control Lorry!

There are in my book two types of risk. Demonstrated risk where there is previous evidence of that risk causing real harm to life and if you like suspected risk where there is no evidence of a threat.

We all know that aircraft crash in strong winds and shear and do so on a continuing basis. We have wind limits as well as cross wind limits to work within but still the crashes happen.

What do you do? do you drop the acceptable wind strengths and make travel by aircraft less reliable. Do you train pilots better or give them better equiptment? But that is a demonstrated risk which is known and which we appear accept.

We know that flying into dense ash can stop engines that is a demonstrated risk with a couple of incidents to prove.

But light ash has a suspected risk only! does it warrant the massive cost and destruction to the aircraft industry that we have bestowed on it mainly demanded by media hype and scaremongering?

If you have evidence that light ash can stop engines in flight show it?

No one doubts dense ash. That can be seen and mapped but light ash cannot. For that reason we have computer generated mathematical forecasts of where it may or may not be.

But frankly until there is some evidence I personally have no fear of flying in clear air which may hold the equivalent of half a thimble full of talc in a five bedroom house to me thats paranoia.

Unless of course you practically prove otherwise and not by another load of mathematical calculations.

I totally support more inspections on aircraft flying in light ash as my only concern as a pilot is damage that can bring an aircraft down (and not increased maintenance cost) but to close huge blocks of airspace on an as yet ungrounded fear is overkill (excuse the pun)

Pace

For example, in this note you said
and, when I said in this note that you replied that I thought these statements seemed quite clear. Did I misunderstand?

PBL

PBL

Did I misunderstand? NO ;) The piece I placed above still does not use the word ZERO which is very different to a statement saying "has not shown to be a risk".

low level ash has NOT shown itself to being a risk to life to date! that may change although I very, very, very, much doubt it.

It may shorten engine life and as such increase costs but I challenge you again to name one situation in the whole history of aviation where there has been a situation where entry into low levels of ash have caused a situation where life could have been threatened?

We are probably both being pedantic in our use of the word risk and probably both have differing interpretations of the word risk?

Mine is more differentiating between a known and proven risk and a feared percieved risk which is not yet proven.

Because the one is proven while the other is not it does NOT mean the other is zero risk (if you get what I mean :E

There is a much higher known risk of being downed by birds what are you doing to close down coastal based airports and chopping off huge blocks of airspace in the migration season as has happened over light ash?

There is a saying that no one ever built a statue to a committee yet there have been too many committees involved in all of this and all with their own agendas again if you understand what I mean ;)

Pace

There is some miscommunication here concerning risk.

What is missing is the statistical term called "expectation" which is the product of the probability of an event multiplied by the cost if the event occurs.

That is why you still fly given the fact of bird strikes:

Probability of birdstrike times cost of birdstrike = expectation value.

Furthermore, we manage the birdstrike probability down as far as we can by removing food sources, using bird scarers etc. We also alert pilots to the proximity of wildlife (or at least Australian NOTAMS do)

We also manage the cost of a birdstrike down as far as we think it is economically viable. That is why we require engines to be able to deliver thrust for so many minutes after ingesting a standard bird.


Now take Volcanic ash.


We manage the probability of hitting it by having VAAC's, forecasts, closing airspace.

But at this time we cannot manage the costs down if ash of sufficient density is flown through.

To put it another way, we cannot build an ash proof aircraft or engine.

Rather, we cannot agree on what constitutes "standard ash" against which to test or regulate. There's no such thing as a bird-proof engine, either, if the ambient bird density is high enough...

Citation CJ2 Volcanic ash encounter pictures
 

I've received these pictures and since I haven't found anything related to this event listed here, I'm posting the pictures.

It's a PDF file so I've shared it in this link:
http://db.tt/qz74EL

I don't have anymore info other than the pictures, sorry.

A volcano in the Gulf Coast would get rid of that nasty oil spill. :cool: :rolleyes:
Why they think the oil leaving the "loop current" for the Gulf stream (which heads for England) is a good thing is not for me to reason why.

Pugachev Cobra
Nope, that has nothing at all to do with VA and the pix have been done to death. Not digging at you, just stating the fact.

All else Yes, it's those pix again.

[YAWN]
Been there, already got the T-shirt.....
IT'S A HOAX!!! (Something else unpleasant happened to this engine, during MARCH ie. before VA became an issue).

Already been through this thread on 19th May. Didn't you even look at the 'properties' of the picture before wrapping it up and posting it. (I bet it had a date in it!!)

Do keep up!

There is also no such thing as a standard bird either.

The environmental encounter regulations are based on probability of encounter. The probability of encounter considers historical experience. Thats why the Feds want all bird strikes reported so as to approximate the sizes, quanities per engine and results. The encounter stuff obviously contains all possibilities of avoidance (both by the birds as well as man). Additionally it keeps track of nature changing by virtue of things like the canada goose etc.

The results of the encounter also consider the good and bad point of changing technologies in the product (high-bypass, wide chord fan blades, FADECs etc. etc.)

When it comes to volcanic ash and super cooled droplets the data to base a standard test on need to consider how often you expect to encounter any given size and density per minute as well as available technolgy within the aircraft to withstand the encounter.

The prioritization for answering the questions about designing to a known standard would also consider what level of standard provides a freedom from risk of an serious result to something ten to 100 times better than the overall risk we are flying within today.

So it seems that since the average operations today in a volcanic ash enviornment have not exceeded the risk floor of 10 to 100 times better than the average risk from all causes, that maybe we should be chasing after some bigger fish like super-cooled droplets in both avoidance and capability.

BTW, cost doesn't enter into setting min safety standards but of course does enter into everything else in how to run a business.

It does, sometimes quite centrally, depending on which jurisdiction you are in. There is a well established principle of English law called "ALARP", which is short for "as low as reasonably practicable", and in English law the providers of equipment and services which are safety-related are required to reduce risks ALARP.

The ALARP principle is also used in other jurisdictions.

Reducing risks ALARP means, roughly, that risks must be reduced until the cost of reducing them further becomes "grossly disproportionate" to the benefits.

PBL

Turbine cooling system temperature
 

On 30th May I posted that I had been trying to discover the maximum temperature of air inside turbine blades and other parts of the cooling system.

I now have an answer for one type of (high bypass) engine: the air can be 650 to 700 C degrees. This vould be relevant to any discussion about VA going through the engine core, since this is quite close to the suggested melting point of the ash and therefore the ash could at least in theory block the cooling holes in a liquid state. This is presumably more problematic than considering blockages due to solid, very small particles.

The same source suggested that there are also concerns about melted VA hitting the outside of turbine blades after going through the combustor. Some surface chemistry possibilities that do the blade no good, apparently. Again, it's all a question of how much VA......?

brooksjg

Can you provde more support, link, personal experience, etc. that suggest that the melting point of VA is "quite close" to the cooling air temperature of 650-700 C degrees in a turbine blade?

I don't recall that there is any documented cases of melted VA inside a turbine blade

I'm glad you said that....

I've seen various 'melting points' for VA mentioned, some early in this thread. However, since they were considerably lower than the figure I 've now been told for the max air temperature in the cooling ducts, I sort-of discounted most of these lower numbers as incorrect - otherwise, as you suggest, VA would have melted and evidence would surely have been produced from previous encounters. The other problem is that glassy materials with high silica content don't have a 'melting point' as such - they soften / liquefy over a range of temperatures.

But saying that such-&-such could not have happened is not the same as failing to find evidence that it ever did.....

I'm not in a position to clarify this and further speculation would not add value. But I, for one, would like to hear more from people who do know the correct answers. An information vacuum seems to have occurred!

That's the way it is sometimes when you always wished that you knew more about a subject.

The good and the bad about this vacumn of knowledge is that the really significant findindings get reported and leak out within the industry while the business as usual stuff remains burried in the logs. That was the way it has been with bird ingestions as well.

Hey guys, there never was any vaccuum. Every profession has sufficient alpha animals amongst them to fill the void with whatever limited knowledge they have. It makes for boring reading, though. Here we have two groups: Those who got it, and those who will never get it. I am stunned that after decades of painful lessons and rules written with blood, so many still think that they, and only they, have the right answer. I've had it. Over 'n' out!

I wish it were that simple!
There are at least three groups at the Sharp End!
- the certain (but possibly wrong) sceptics who are not supported by the current (or previous) rules about VA;
- the certain and uncertain 'conformists' who may prefer to go along with whatever's thrown at them rather than appear radical, non-conformist, awkward-squad, etc.;
- the other sceptics who go along with whatever rules are current but are uneasy about the 'certainties' as presented.

Then there are other players:
- regulatory bodies, including some people who seem uncomfortable with any form of risk management. Why such people ever end up working in regulatory organisations where the main activity is essentially risk management defeats me. Elimination of risk will never be an option - if it were, aircraft would never have been developed at all!
- businessmen, accountants and shareholders wanting to make money out of the industry;
- governments who suddenly realize that whole economies will go rapidly down the pan without aviation.

Complete certainty is not an option either - I doubt there ever will be any about VA and its risks.

Regulation based on 'Zero VA' was clearly never based on observational science. It was an easy decision until some VA actually loomed into view, then its weakness became self-evident (and proved by actual experience). The current permitted VA maxima are also a line-holding exercise in the continued absence of real research. The forecasting system is also evidently prone to errors, especially over-estimation of coverage, again presumably due to lack of real data collected by direct observation of the ash clouds.

Somehow or another, the industry must pull together and spend the money, on engine research and on atmospheric observation (not forecasting / prediction, if certainty about ash location and density is the requirement).

The only element entirely beyond control is the volcanoes.

I'm sick of this. Comments slagging off about regulators are just unfounded.

Here are the documents and research details to date.

ICAO volcanic ash contingency plan, edition 2 September 2009.

Documents

ICAO manual.

http://www2.icao.int/en/anb/met-aim/...Amend.%201.pdf


ICAO taskforce:

ICAO NEWS BRIEF ICAO News Centre

Sandblast effect ...
 

From down the back the other day, noticed the painted RYANAIR logo on both my favorite airline's winglets had been significantly 'sandblasted' with the letters 30% obliterated. When I got off, I noted that the spinner spirals on the engines looked similarly beaten up.

Is this ash damage? I don't recall noticing such wear and tear previously. If so, are Europe's workhorse airlines now getting a better picture of what's it costing in extra maintenance ?

lomapaseo
Not sure but I think a photo in this article (link below) shows that very thing... or if not melted then certainly able to clog the cooling holes?

Why Can't Planes Fly Through Volcanic Ash? NASA Found Out the Hard Way | Popular Science

TyroPicard

Yes those pictures have been posted many times within this thread. They closely match the known severe events affecting engines.

The discussion just above had to do with VA melting inside the turbine blades if the cooling air is hot enough.

as always follow you FCOMs, it's easier to change those than to convince all pilots of the finer points :)

Risk management!
 

Well, you would have to be a fool or suicidal to go fly in such an ash cloud:

http://images.huffingtonpost.com/gad...2102_large.jpg

But it took a bunch of pen licking scientist and bureaucrats to stop me from flying in this kind of weather: (And that's what the weather actually looked like over Belgium during the first NO-FLY weekend!) :ugh:

http://www.thedailyparker.com/conten...light_3096.JPG

Let's hope common sense will prevail if this or another volcano starts erupting again.

Horses for courses, as they say. I reckon, however, there will be some little pink bottoms that will need levering off seat cushion buttons when one of the 2 engines goes POP mid-ocean with 120-180 minutes at MCT to nearest:)

You mean when a bird goes down the intake BOAC?! :)
Or the fuel calcs are wrong (or the wrong fuel gauge fitted!) and plane runs out of fuel?!
Or the water sed checks aren't done correctly and the donk flames out cos it's trying to burn water?!

Can't be anything to do with ash 'cos us engineer's can't find any damage from VA!

Somebody mentioned sand blasting on a Ruinair flight; Atmospheric sand, grit, pollen, small parachutists, what-have-you, is constantly eroding surfaces long before Erecckkkllannnoorrookkkfffic exploded. If you pilot chaps have a close look at your pitot probes and leading edges you'll see they're all eroded to some extent.

- erm, no, unless you have records of bird strikes at FL400 mid Atlantic?:ugh: - how many turbine blades do you actually section each day?

Not an attack on your post BOAC (difficult to express intonation in text!), simply pointing out there's a lot of stuff that'll bring an airliner down before VA does.

I have seen no evidence of VA damage. I know of no other engineer that has. Friends of mine work in engine bays as well as line stations, the grapevine would quickly flash up evidence of this nature, if it didn't Sunfish would!

You're right, I have no record of birdstrikes at FL400. Nor have I any evidence of volcanic ash damage.

residual:

That's because the regulators closed the airspace before evidence accumulated.

...and my elephant scaring crystal is working too, no elephants in my garden :ok:

Sunfish: errr - what are you actually 'sick' about? Comments about inappropriate regulations? Inaction? Slow response?

I assume your ICAO reference is intended to reassure that ICAO is rushing about doing stuff and the results will be Real Soon. The meat (such as it is) of the press release says:
Looks like a bit of 'Manana, but without the same sense of urgency' to me. Decide what report to write by 1st August and then spend the next 9 months writing it. But reports of any kind do not actually DO anything. On this timetable, there'd be no prospect of even getting the VA concentrations harmonized by mid-2011.

And 'options' are quite easy to write up. Selecting and implementing the right one (starting May 2011 at earliest) might take a bit longer. Slow? Inactive? Complacent? Pretty-much as useful as a Chocolate Teapot? You choose!

'Never mistake Activity for Effective Action'.

And meanwhile, in Another Part of the Forest, Easyjet is making PR capital (even if not actually gaining useful competitive advantage) by putting IR cameras on some of its aircraft at the cost, it says, of £1m. (see other posting). Well, at least it's action, even if uncoordinated and possibly not terribly useful.

Solution?
 

Stop blaming someone else, you know damn well its was the airline industry who set the standards and therefore its those who are responsible.

Rather good perceptive posts above and in some cases sounding at odds with one another :ok:

The status quo takes a long time to change all the various opinions in our industry. Especially when it seemed to "get by" and more pressing problems du jour arise.

(attrib above to Mr Prata)

Yeah - right. You get '5 minutes' (or less) warning of 'VA Ahead' - then you have to contact ATC, request a route / height change, wait for ATC to decide based on other traffic, etc. and action whatever change is advised. Err - not in 5 minutes, if everyone on your route and its reciprocal, at several different FLs, are all going through the same process!!!! Utter chaos would result. It's all very well arguing about 'Captain's Authority' deciding where the aircraft goes but in controlled airspace it's not a realistic scenario to actually exercise it as apparently proposed.

This might be worth watching:


Volcanic Ash: The Ticking Timebomb
Tuesday 08 June
8:00pm - 9:00pm
Five

Documentary exploring the likelihood and potential global effects of the eruption of Katla, a huge volcano lurking under the Icelandic ice. Katla is five times the size of its neighbour Eyjafjallajokull, which recently caused so much travel disruption when it blew clouds of volcanic ash into the atmosphere. Historically, every Eyjafjallajokull eruption has been followed by a flare-up at Katla. If such an eruption were to happen now, it is predicted that European airspace would be closed down for 18 months.

And what superb specimen of homo sapiens predicted that? Donald Duck?

It is unusual for airflows over Iceland to track towards the UK so how come 18 months? if that last load of scaremongering like the rest of the so called scientific scares from everything from BirdFlu to ash ever came true?

Oh well maybe one day they will actually get one right who knows? But that will probably be more luck than anything else or in that case bad luck :ugh:

Pace

I note they manage to work in global warming as a factor, although in a most unconvincing way.