No, it's not like that at all. Just like with shoes, you expect engines to wear out from normal use, but no-one knows how accelerated any wear may be, if there is any increase at all, with varying levels of ash contamination. To use your analogy, it's like expecting a normal pair of shoes to stand up to walking across a rough lava field - they just won't last as long, but you can't predict how quickly they'll wear out.

What is certain is that the ash will build deposits that do more than just cause wear - they will cause hot spots and thermal stresses or melting of components as well as affect the internal thermodynamics of the engines. How rapidly these deposits form is unknown. What level of deposit is safe is unknown. How big these deposits can grow before detaching is unknown. the level of damage caused by deposits breaking off is unknown... Therein lies the problem; there are too many unknowns to determine if flying through this amount of predicted contamination is safe.

I thought this might be interesting. The previously grounded BAe146-301 from FAAM is currently airborne over Scotland at FL260. Let's hope it provides more answers.

http://www.faam.ac.uk/index.php/position

Someone posted that it was measured at over 2000ppm. The NASA aircraft that was damaged, flew through 600ppm I believe.

Correct me if I'm wrong, but if a an engine is producing 10,000lb of thrust, it would be consuming 0.01lb of dust per second ppm. Or 36lb per hour (16.36Kg).

600ppm would mean 9816kg per hour passing - and melting - through the engine.

That is correct. (If the aircraft is already cruising at its best level)

theoretical mathematical model
 

For everyone who is disgusted that the Met Office are using "theoretical mathematical models" to FORECAST the ash movement... wtf do you think they use for all their other FORECASTS? Little pixies? Oracles? You've got to start from something, and microscopic radioactive particles seams like a good enough starting point for me - seeing as it's only been running for a week.

Theoretical methemtatical models
 

Dusty B - Agree. But that is also why we need the physical empirical evidence to go with it. Now (and for the last 5 days) we've had the chance. May be too late to enact a solution based on the 2 observations - theory vs actual. But, it will bode well for the future if this scenario arises again. Sorry to bang on, but we need the evidence eventually and the level of 'test flights' thus far and how they've been executed does not appear to show the needed due diligence.

Funnily enough, the model is being verified by observed data...

And of course aircraft are transitting UK airspace - its open above FL200!

BoughtTheFarm, you're right - test flights need to be instrumented and done properly, covering the whole range of flight levels across all areas, rather than just a jolly around the eastern Atlantic at FL whatever which proves nothing. Even then, If you go fishing (test flight) you might not catch a fish (ash) , but it does not mean there are no fish (ash) in the sea. (air)

With the greatest respect guys, and I know it's not really 'any of my business' but the mods have repeatedly asked for the 'spotteresque' posts to be kept out of here. Can see their point, it clutters up interesting debate and they are working overtime keeping the thread tidy.

I'll shut up myself now.

BA planes ...
 

Just heard that the BA longhaul planes on the way to LHR have been told they are not landing there today ...

Unfortunately, it just seems that there is a sort of subculture of (usually) right-wing people in the UK who are obsessed with the idea that the Met Office is plotting against them. This thread has now reached the point where the same people who were yelling that Gordon Brown was at fault for closing the airspace and it wasn't really a problem - no link or citation has yet been produced to support the idea that it was Brown's decision rather than CAA, NATS, or VAAC - are now yelling that Brown should really intervene and have it reopened rather than "hiding behind NATS".

And, apparently, a volcano going off in Iceland is Harriet Harman's fault. Frankly, you could cry.

Also, with regard to the link to The Register: when I was a tech journalist (like Andrew Orlowski) we had a saying that if it was on the BBC it was probably out of date, if it was on ZDNet it might be right, if it was in Wired it was probably right but overhyped, and if it was in the Reg there was no way of telling whether it was right, wrong, or pure pub drivel. I am not aware that the former fanzine editor has any competence to say anything at all intelligent about modelling ash dispersal, and it would vastly improve his product if he were to shut up more often.

Dusty B:

Fair enough to use mathematical models for forecasting weather patterns and cloud movements. This is quite scientific and has years of proven ground.....BUT to use theoretical mathematical formulas that have never been tested to predict the levels of concentration of the volcanic ash that is dangerous to aircraft would appear to me to be verging on irresponsability.

On the other hand, one has to say in their favour, that if they are not provided with electric screwdrivers, then they are doing a very good job using a hammer for the screws......

NATS operate with a licence from HMG, and all other European ANSPs operate similarly with a licence from the state. NATS must operate within the terms of it's licence and all of the other rules, regulations and laws applicable to an ANSP. The 'law' governing flights in ash conditions is the ICAO document referenced in previous posts. Who exactly could be sued and for what reason? Who has done something wrong or likely to bring harm to others?

BD

Wippersnapper

So let me get this right. There is absolutely no danger in the BA aircraft approaching LHR in this lovely weather, but they are being refused permission because NATS is concerned about the long term damage to their engines. Is this correct?

Very wrong. You need to calculate the air flow through the engine. Nothing to do with thrust.

An example. Which I based upon figures from the Canadian VAAC, which seems to use a distinctly better model than the British one, with results divided in low, medium and high concentrations. Low goes from 10 to 100 micrograms per cubic meter of air. If you consider a plane flying at 180 m/s, an engine with a capture area of 3 square m, and a concentration corresponding to the upper limit of the "low" concentration, over ten minutes (an estimate of the time to cross a lower level cloud, after takeoff or before landing), you absorb roughly 0.3 grams of ash per engine.

@DjerbaDevil

There are a couple of points where you misunderstand:

1. The VAACS model is not predicting concentration. It explicitly stated in the earlier graphs (although appears to have stopped doing so) that density of the "cloud" is unknown. This is not to excuse the process, but merely to state a fact. Maybe the ICAO should alter their process to not consider such models where concentration is unknown, but the VAACS model is officially approved by the ICAO.

2. The VAACS model does not try to suggest at which concentration of ash engines might be damaged. That is for the engine manufacturers to decide. Since they do not know, they recommend concentrations of zero.

It looks like common sence is about to prevail. The Met Office model is about to be given the heave ho.

I don't know if the link was posted yet, I've not been following the thread assiduously, but here is the NASA technical report. I hope it is helpful. It seems to me to conclude that flying through a diffuse cloud can cause hard to see damage that nonetheless has a major impact on engine lifetime and hence safety.

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

SUMMARY

In the early morning hours of February 28, 2000, the National Aeronautics and Space Administration (NASA) DC-8 Airborne Sciences research airplane inadvertently flew through a diffuse plume of volcanic ash from the Mt. Hekla volcano. There were no indications to the flight crew, but sensitive onboard instruments detected the 35-hr-old ash plume. Upon landing there was no visible damage to the airplane or engine first-stage fan blades; later borescope inspection of the engines revealed clogged turbine cooling air passages. The engines were removed and overhauled at a cost of $3.2 million. Satellite data analysis of the volcanic ash plume trajectory indicated the ash plume had been transported further north than predicted by atmospheric effects. Analysis of the ash particles collected in cabin air heat exchanger filters showed strong evidence of volcanic ash, most of which may have been ice-coated (and therefore less damaging to the airplane) at the time of the encounter. Engine operating temperatures at the time of the encounter were sufficiently high to cause melting and fusing of ash on and inside high-pressure turbine blade cooling passages. There was no evidence of engine damage in the engine trending results, but some of the turbine blades had been operating partially uncooled and may have had a remaining lifetime of as little as 100 hr. There are currently no fully reliable methods available to flight crews to detect the presence of a diffuse, yet potentially damaging volcanic ash cloud.

Ok.

So (180m/s x 3m) *10microgram=5400microgram/second.

5400microgram * 10*60= 3.24grams in 10 minutes.

At a higher concentration (still low) of 100 micrograms per cubic meter of air it would be 32.4g per engine per transit through the layer.

This is assuming 10 minutes transit, I believe the cloud is now down to FL10 and below isn't it?

"It looks like common sence is about to prevail. The Met Office model is about to be given the heave ho."

So we are going to use common sense for future weather predictions as well are we?

200 years of science, some of the most powerful computers in the world and all we needed was common sense instead.

peter we
 

I have just been giving the NASA DC8 report a once over. There is no statement of the ash cloud's particulate parts per million during the 7 minute encounter but there are two graphs, 7a and 7b, of what happened. 7a shows the sulphur dioxide concentration against time which peaks at about 800,000 parts per trillion by volume. 7b shows the aerosol number density against time which peaks at about 28,000 per cubic centimeter. Can anybody explain how these figures translate to the concentration of particulates in parts per million (physics a bit rusty!).

One bit of good news for the brave souls flying the test flights is the following quote from page 13 of the NASA DC8 report:


Sounds like an on-the-wing de-coke!:)