Jet engine failure modes with ash ingestion
 

Understanding why a jet engine should flame out when heavy concentrations of ash go in the front end (compressor and combustion chambers) is just common sense. We also know from experience of this that it is possible to glide down for 15 mins into some cleaner air where the engines can be restarted.

However, there is another failure mode which is much more of a problem and potentially terminal for the engine.

If very fine material that the compressor and combustion stages can happily swallow enters the engine, the risk is to the turbine which in normal operation must be cooled. This risk arises because the airflow past the turbine is sometimes several hundred degrees above the melting point of the turbine material. The cooling air exits through a myriad of small holes in the surface of the blade ensuring that the blades are encased in a cocoon of cool air.

Clearly quite small particles could affect this cooling flow but even worse, depending on the composition of the particles, the temperature can cause some of the particles to change their nature and form a glass like material that can build up in and on the blades. In the worst case such a process, when the engine is running normally, could destroy the turbine in a minute or so.

Apologies to all those who understand these matters.

Time to buy stock in engine manufacturers/re-builders methinks.:E

From the Rotorheads forum
 

BBC News

Offshore Helicopter Operations

Lord Adonis would be best advised to keep his mouth shut and seek some advice before spouting of.

Irrespective of whatever anyone on here thinks about the decision to close airspace in the UK, the glaringly obvious FACT during the whole episode is that none of the incumbent Cabinet Party were visible in the first few days. They only started coming out with opinions when it was clear that the airspace was about to re-open - and even then they didn't know the roles of NATS etc.

Looking at charts over the past 24Hrs, even if using the old criteria the majority of UK airspace would now be open.

It's very easy for politicians to say it was an over-reaction - pity they didn't have the balls to stand up at the outset...

HMG acted very poorly (well, very seldom) throughout this whole episode :=

With interesting line being: "There was no damage and no ash was found in engines."

Another interesting snippet from bbc ( BBC News - Volcano cloud as it happens: 21 April ):

A "tough decision" would have been to accept full responsibility for safe conduct of flights through contaminated airspace whatever the outcome. BA could've been flying all week long had WW simply said that he and his board of directors would do so, irrespective of CAA/Met Office advice. Guess what, they didn't.

Instead, they sat wringing their hands looking for someone else to make the decision and when that didn't come quick enough they turned up the heat on, in this case, our 'unelected' politicians.

Nothing brave about wanting to carry on doing something whilst at the same time looking to apportion blame elsewhere in the event of an incident.

If it turns out it is one of his 747s with a double IFSD I'll look forward to hearing his take on the supposed over reaction on the part of the CAA.

Why should they?! They have done EVERYTHING right and by the book, as per manufacturers reccomendations, as per ICAO guidance, and observations have backed up forecasts. Gross misconduct? I think not. Safety before money - yes.

Should the airlines have done more for their passengers? Maybe. Should the government have done more for stranded passengers of all nationalities? Yup. NATS / CAA / Eurocontrol / Met agencies have done their jobs in the face of increasing pressure and hostility from those losing money.

MOL steps up...
 

From BBC News - Ash cloud chaos: Airlines face huge task as ban ends

Here's your 50p back, good luck hitching to Calais...

Question above ..... How could XXX have issued documents ....

Be careful of using a lay persons intreprrtation of what these documents for the pilots are intended to convey.

Lets get back to the traffic light anology of red light clouds, yellow light clouds ad green light clouds.

It was postulated based on routine everyday maintenance findings that volcanic ash in clouds exists everyday someplace in the world and that some planes fly through it without impact on the flight. Thus the Green-light cloud concept.

Then there are the rash of events following a major eruption like Pinatuba where the cloud being unseen and untracked produces any symptoms described in detail in the OEM warnings that should be reacted to by the flight crews and the ground engineers This at least defines the Yellow clouds that were either not identified and tracked or that there was no intended avoidance. The OEMs thus have a duty to warn that abnormalities may occur in this situation.

And finally the Red Light cloud that represents the worst of the combinations of either not being tracked or not being avoided and at the same time producing major symptoms in combination of smell, sight, windshield effects, Pitot effects, engine symptoms and an immediate need to throttle back engine descend and turn away.

I believe that what is being dealt with today is the realization that all clouds are not bad and that traffic control and alert pilots can still lead to safe flights.

Here we go: Finnish AF has now inspected the engines of the F-18 Hornet, which were allegedly damaged in flying into the volcanic ash. You know, the ones of which fine pictures were shown on tabloids and even reputable papers.
Finding: NO DAMAGE FOUND!!!! Ok, traces of ash, but: NO DAMAGE!!!!

Why am I not surprised....

No, there is a body of normal, rational people of many political persuasions who want to know who made the decision to close all airspace. It is a reasonable question to ask. And in the absence of any hands going up, it is natural to go to the top and ask what role the government played in all this.

And even if the government was not directly involved, they have still instituted and encouraged the recent social atmosphere where no risk-taking is allowed - which precipitated the closure of airspace in the first place. Had this been the 1950s (even with jets, satellites and computers etc,), we would have carried on flying, as you well know.


And BTW, I have flown for two days across all Europe, and not seen a speck of vitrious deposits on my turbines. Ergo, at whatever concentrations we have now, everything is fine. Are you listening, CAA, NATS, Eurocontrol and governments??



Oh, and as an aside, why were all those who were against the closure of airspace deleted from this site? Especially as we turned out to be correct, and the closure was excessive. If that is not political/judgmental, I don't know what is.


.

Some people tend to forget the fact that during this NATS has been losing heaps of money as well. Not the sums the larger airlines have, because NATS profit is miniscule to the likes of BA. Taken as a percentage of earnings though, NATS have lost as much profit as any other organisation - not far from a months worth of profit down the drain.

And, the way these things are written, often pilots can't figure out what they are trying to say. The human interface on our NOTAMs and other flight papers is primitive to say the least. Obscure abbreviations and lack of graphics with coded number and letter groups mean it's so easy to overlook something important. Everything is in caps since 1930's teletypes couldn't do lower case.

We will therefore be standing by for Lord Adonis' resignation. He is at the top of the whole tree of bureaucrats.
Indeed. Well done WW for actually pushing it through and launching all those flights from overseas (was it really 26 ?) into London to arrive the minute it was planned to open. I may have had harsh words about his commercial and managerial decisions in the past, but am right behind him on this one. Bear in mind, all those going on about the commercial aspects, the principal beneficiaries of this were the PASSENGERS who were returned home. Sometimes they get forgotten along the way.

Notably the Bearded Wonder didn't do the same at his carrier.

whilst I agree completely that lessons need to be learnt from this whole incident. I am not sure I have seen it stated anywhere that Nats as a company has also lost millions of pounds in revenue during the crisis. Nats has been portrayed as somewhat like a police service of the air. Personally if I had been in charge of Nats (god forbid some may say ! ) i would have said that the airspace was open and it was up to the caa , government and the airlines to make the decision to fly or not. I would put forward that Nats overstepped its remit and to listen to junior people being allowed to appear on TV and advise passengers what to do or not do was a total farce. I have not seen the new ceo at any time on tv or senior board members! I think the airlines were well placed to make their own judgements , obviously with government and met office guidance. If , as seems likely it was a case of possible long term engine damage as opposed to aircraft having in flight shutdowns then That is a commercial decision for the operators.

I'll try to give a link, but it is in Finnish...

Puolustusvoimat: Ilmavoimat raportoi tuhkapölyn vaikutuksista Hornetin moottoriin

Hooray, well said.

I have been asking for a map of NOTAM sites at the beginning of all NOTAMS for over 20 years. (especially for PPLs, where route NOTAMS are not always available). Yes, graphics for taxiway closures would be nice too, instead of everyone in the pilot community spending hours trying to find exactly where W1 and F6 are.

And little things like grass-cutting, bird scaring and firework displays being the top lines and waaaayy down the bottom you find that the ILS and radar are out of action.

The guys and gals who make NOTAMS should be tasked with reading all the NOTAMS within 4 minutes (all we are allowed) and if they fail, they should be put out to grass.

.

And where, one might ask, was the BIG Mouth of Aviation himself during all this?? Normally willing to push every operational and safety parameter to its absolute limit, suddenly the Big Mouth of Aviation goes quiet?

Is he turning over a new leaf - or suddenly aware that safety considerations need considered discussion rather than a bullying Big Mouth?


.

Translation of the Finnish AF report on F-18 ash ingestion
 

Via Google translation:

So not quite no damage, but perhaps better characterized as limited or minimal damage.

- GY

OK, the figures are in the public domain. NATS income is circa £2.1 million per day and running costs circa £1.86 million per day, you can do the math :)
Not our job.
Nope, NATS operates on a licence from CAA (the goverment) and as a part of the conditions of it's licence must abide by rules, regulations and laws, including the ICAO guidance etc. which the government signed up to. Every ANSP in Europe operates similarly and, as you seem to have missed it, a lot of european ANSPs closed their airspace. Indeed some countries went further and banned all flying, but HM Government didn't take that step (and NATS don't have that remit).
Hhhmm, you must have missed NewsNight when Jeremy Paxman interviewed the new CEO. All the spokesmen on the TV etc were ATC facing senior managers (Alex Bristol Head of Strategy & Investment, Jonathan Astill Head of ATC Prestwick Centre, David Harrison formerly GM ATC Manchester now Head of Safety and so on) I think a member of the board wouldn't have quite the same street cred as a senior ATC manager.
No it's not a commercial decision, it's a safety decision. Pilots may only fly aircraft with a relevant air safety certificate, pilots may only fly aircraft for which they have a valid licence. This is done for many safety reasons but a big one is public safety. I wouldn't want some gung ho flyer leaping into the skies when it had been deemed potentially unsafe to do so and have the wreckage landing on my head thank you very much.

BD

I am amazed at the amount of people looking for heads to roll when all those heads did was follow the rules. Nobody can say any different .. Yes you may feel that the rules were over the top and that may well be , but herd ( or CEO opinion ) in itself should never be responsible for the convenient ignoring or sidestepping/ bulldozing of those rules. Neither should a 6th form physics experiment. I am sure there was a tremendous amount of work for the engine manufacturers to do in order to change their position and explicit rules in regards to volcanic ash.

I am relieved that things seem to be settling down now as my own company has been suffered some serious economic damage in the six days and the medium term damage we are unable to quantify at this time, still though at least we can now operate again.

Just to show what we are talking about here is an actual volcanic ash advisory from pilot departure documents:

Which references this message that may or may not be included in the paperwork:

You can actually figure out what it says if you guess a little - e.g. PSN must be positon since it is followed by a lat long but why are we still using decoder rings in this era of high speed internet and laser printers? A few more vowels, a little punctuation, graphics and some formatting sure would make this easier to read. I realize there are much better versions of this advisory available on web pages but often the terse teletype text is all that makes it to our paperwork. Of course, if something goes wrong, they'll have the full color graphics at the hearing.

Apologies for talking a little shop with this operational pilot stuff on the ash advisories.

Looks to be getting pretty active again in the past few hours, this morning it was only a very small amount of cloud around it. Third picture down

Link: Mulakot - myndavelar

Let the Great Experiment begin...
 

How can this be when the CAA's Revised Airspace Guidance last night requires airlines to:

· conduct their own risk assessment and develop operational procedures to address any remaining risks;
· put in place an intensive maintenance ash damage inspection before and after each flight; and
· report any ash related incidents to a reporting scheme run by the CAA?

Depends on the viewpoint; turbine bucket with ash sticking to it does not affect engine performance much. Replacing or scrubbing it might prove costly and time consuming.

Yes I did my "test" flight, thank you for asking.

Ever helpful ATC confirmed that my penetration of VA alert area was solely upon my discretion. I would have appreciated that even more, if they choose some earlier moment to tell me that than post-landing taxiing.

No, the engines did not flameout, stall, show glowing around intakes or props, spout fire from exhausts or increased their respective ITTs erratically & rapidly. There was no st Elmo's fire visible on the screen, it was noon anyway, and no strong sulfuric odour was present.

As I have made the post-flight written confirmation of the above mentioned facts, the maintenance stated that just flying through suspected VA contaminated area does not warrant complete post VA penetration maint procedure and cleared the machine for further flights.

At least now I won't get the bill if the overhaul comes before planned time.

Regarding see and avoid: in severe CAVOK one can discern layers of dirt in the atmosphere. Now I know what I've seen yesterday over mid Italy - it looked exactly as photo on the page 3 of German Falcon flight report. There was no practical way of going around this one, it stretched from the horizon to horizon. And I can tell that regarding my routing, Met office's prediction of VA spread was frighteningly correct.

are you saying they are not following the CAA guidelines ?

doesn't it say if an aircraft flies into a low ash density area that damage inspection has to occur after the flight ?

Met office report Northern Ireland 1400 BST — ash layer around 8500 ft, at least 500 ft thick - visibility greatly reduced with a strong sulphur smell.

Unconfirmed: Source BBC.

BBC reporting that pax from QF32 ( Heathrow - Singapore ) are contacting them. Flight is boarded but holding pax on the ground pending an improvement in the "air quality ". The skipper is telling pax that the ash concentration is above the levels in which Qantas are happy to fly.

No - we're not regulated by the UK CAA anyway and they did they homework; risk was assessed , procedures put in place after liaising with local CAA. Leading edges, props, engine intakes and transparencies were checked for abrasion damage or dust accumulation. None was found and acft was returned to service. Legal - yes, sufficient - couldn't say.

Clandestino - thanks for the clarification - makes sense.

btw I'm glad flight wasn't eventful for you.

A Tough Decision?
 

Rab-K - Your earlier post is twaddle. BA would not have just kept flying from day 1. After 5 days on FIR closure a DECISION needed to be made. Keep up the same position or open airspace. It's far easier to close it on safety grounds than open it on the same. But at some point a decision needed to be made. If WW helped get that one way or the other then good.

Inaction and hesitation are no more the friends of safety than knee-jerk, just do-it are. After 5 days and most EU FIR's starting to operate the UK was in danger of being the 'first ones in and the last ones out'.

And anyone who thinks that commercials are not heavily in play on all of this are much mistaken. No Buck, no Buck Rogers as they used to say in Flight Test.

As I said, I'd sooner have people who step up to the plate and make a decision than keep examining their naval fluff until someone else makes the decision for them.

We didn't go to the moon by waiting for the all clear from every quarter let alone getting to and from JFK. 'Decision height'. Captain Walsh called it.

HIAL update at 19:00 - airports closed until Thursday morning.

Volvo_Aero about Ash
 

Volvo-Aero has a short piece about ash in their jet engines, see the following url:
Actual - Actual : Volvo Aero
In princople they state that their engines can stand rain, ice and some birds, but not ash.

One can simply divide by the by-pass ratio of 4.3.

But there is the issue, under which conditions is the mass flow rate 1177 lb/s? We probably should consider a density figure at pressure and temperature corresponding to a typical cloud level. You can take standard atmosphere data etc.

However there is another estimate, based upon speed and diameter. Take the fan diameter, 74.1 in. Calculate the area. Divide my the by-pass ratio. If I do that, assume a speed of 180 m/s, for 0.3 g/m3, I end up with actually a very similar figure, 126 g/hour (assuming no algebraic error...) Of course one would hope crossing an ash zone would take less than an hour.

BTW, indeed the new threshold figure of 2 g/m3 comes across as not very conservative. I would have expected them to pick a figure more like 0.5?

A Danish perspective on detection ...
 

tolerance levels
 

In the UK MET charts posted by kyloe (#2186) the black area according to the label is the zone "that exeeds accepted manufacturer tolerance levels"

I´ll appreciate if somebody can give me the figure for that level.
¿some ash concentration? ¿An envelope for all turbines?

Here´s a link to new hi-res pictures of the Hornet engine published by the Finnish Air Force today:

Puolustusvoimat - Frsvarsmakten - The Finnish Defence Forces

Like has already been said, no significant damage was found, only "concentrations of foreign materials", partly melted, but it´s plain to see that these spots do not even come close to blocking any of the cooling holes in the turbine blades. On the other hand, the occurrence took place in the morning of the 15th, before any restrictions even had been put in place.

paidworker
 

I almost wrote, "Surely not the Nuremburg defence", but decided against. Instead may I refer you to the following quote:


Actually I think it was Douglas Bader!

As others have pointed out, there was obviously a problem with the rules. There is never zero volcanic ash in the atmosphere. We have always coped around the world until an invisible plume hit the UK. Thank heavens we have leaders like Captain Willie Walsh to sort things out.

Regards

S:)

Forecast models and charts fairly consistent on a gradual change to southerly winds, at least over the UK, overnight Friday/Saturday,

UKMO surface charts to T+120
Metbrief - Met Office Analysis and Synoptic Weather Forecast Charts via Wetterzentrale

300mb forecast charts to T+120 (rh side of page)
CRWS Jet Stream Forecast Map Menu

Here's hoping those lows approaching from the SW are more vigorous than forecast.