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.


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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?


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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