Ash clouds threaten air traffic

[captainpaddy]

Oh good lord, I said I was done here! The air in a jet engine.....oh never mind. I just can't do it anymore. A bird and an ash particle are kind of difficult to compare don't ya think? Look at some bird ingestion test and tell me if you see the bird drifting towards the outside of the intake from centrifugal force before it hits anything.......

[mm_flynn]

Originally Posted by brooksjg

Err - no. The (now very old) USGS report on Pinatubo includes several notes about aircraft damage found well AFTER flights that could have caused it! The authors commented that the reason that there's no location given for some of the tabulated incidents is that no-one knew where they happened!

Some perspective on this. The only incident where there is no indication the crew knew about the ash at the time is

Originally Posted by USGC incident 91-14

Indications that aircraft flew through volcanic ash cloud were apparent only after aircraft underwent ground inspection in Kuala Lumpur, which revealed abrasion of plexiglass landing light covers and navigation lights, which were totally opaque. Cowling intakes were abraded and rough to the touch, while compressor blades were remarkably clean. Landing gear bays were covered in ash with ash sticking to oily surfaces. No apparent damage to windshields

There is very little additional information on this flight (not even who the operator was) so unclear if this was CAVU damage, night or IMC.

USCG to make the point that for several years there were issues with window and paint degrading and sulphate build up in hot sections for aircraft effected by the gas cloud (which was across the whole of the Northern Hemisphere).

[Intruder]

We will continue to debate this til the cows come home. There will be no resolution until there is something in writing from both the manufacturer and the regulator that clearly states a policy.

Looks like the debate is over, then. Boeing tells you not to fly into volcanic ash clouds. Eurocontrol and several member nations published a clear policy that prohibited IFR flight into areas they deemed unsafe due to the volcanic ash cloud. They assessed the risk and decided it was too high for continued IFR flight. That is the basis of sound risk management when it comes to aviation safety.

There will always be second-guessers. The fact that there were no ash incidents gives clear evidence that the Eurocontrol policy was successful. There is no way to tell how many incidents or mishaps there would have been without the policy.

Airlines now want the governments to pay them for the money they think they lost. What would have been the cost of even ONE crash due to ash injestion? I think the airlines may have saved money...

[lomapaseo]

[quote] It's a law of physics. You start to give ANY MASS a rotational velocity around a point then its going to move outwards.

Sorry but even if the forces are tiny and the movement is small the effect is still there.

However i'm not in a position to state without facts or figures if there would be any difference in ash density into the non-bypass airflow. /quote]



The bigger stuff gets thrown out further,

The stuff at the fan blade roots doesn't get much acceleration, same with birds. The spinner shape is also critical to particles heavier than air.

Pretty easy to model once you've defined the particle size.

claims-counter claims are just that unless you want to take it to the technical section

[mercurydancer]

Oh windytoo..

I do agree that the experts in engineering and airframe design are the best people to assess the actual damage to aircraft there are some precedents which make your logic most uncomfortable.

Challenger space shuttle for a start. O rings which were stiff and amenable to bypass gas when cold. This knowledge was available prior to the flight but was not acted upon by political, managerial and financial pressure. Does that sound familiar? I strikes a definate chord with me in the volcanic eruption saga.

If you wish to compare flight safety in the way you do then you accept the lowest common denominator of safety. If 100,000 people died each year in the UK because of aircraft accident then no one would fly. Is flight safety paramount or something that can be degraded?

Of couse life is a risky thing since birth but risk evaluation depends on known factors or trust. In real life people evaluate risk against benefits. I am not forced to get on any aircraft but that is an absolute. If I do not get on an aircraft then me dying in an aircraft crash is minimal ( but not impossible- the aircraft may crsh into me on the ground). I choose to pay the fare and get on an aircraft because I want to go somewhere of benefit to me. Its not an absolute, its a spectrum of risk. Am I prepared to get on an aircraft not only with the risk of it crashing but me spending days or weeks at great cost not being able to get back to home?

In the past two weeks I have put a plain sheet of A4 paper on my patio table, and guess what - ash deposits. Not every day, but enough for me to wonder what is really up there. I'm no engineer and I have no idea if the accumulated dust on my little A4 amounts to a signficant engine-failing quantity but it makes me think.

The difference between "could " and "will" is easily quantified. Its Murphy's Law.

[Bruce Wayne]

Boeing tells you not to fly into volcanic ash clouds. Eurocontrol and several member nations published a clear policy that prohibited IFR flight into areas they deemed unsafe due to the volcanic ash cloud. They assessed the risk and decided it was too high for continued IFR flight. That is the basis of sound risk management when it comes to aviation safety.

That assetertion is disingenuous.

The issue was not flight into volcanic ash cloud, the issue was flight in an airspace that could have had VA particlates.

There will always be second-guessers. The fact that there were no ash incidents gives clear evidence that the Eurocontrol policy was successful.

argumentum ad ignorantiam.

There is no way to tell how many incidents or mishaps there would have been without the policy

So no burden of proof. Ergo, argumentum ad ignorantiam.

Airlines now want the governments to pay them for the money they think they lost. What would have been the cost of even ONE crash due to ash injestion? I think the airlines may have saved money...

The airlines were financially damaged do to mis-management of a situation, as such yes they should be. They were damaged by the actions of another party out of their control, as such, they have scope for recompense of damages.

[mercurydancer]

Brucewayne

If you can tell me the difference between a volcanic ash cloud and airspace that "could" have ash particulates in it then that would solve the huge multimillion quid probelm that airlines in Europe face.

I dont want to get hard-nosed on logic but you cannot use burden of proof on the fact that accidents have not occurred. Burden of proof can only be validly applied on an event that has actually happened. My Latin is a bit rusty but reductio ab absurdum is the term which fits. In this context it means that you would accept any risk because you do not recognise it as a problem.

[NutLoose]

I have to give Thompson Kudos for this approach...

Thomson Airways ... Personal Update! - Key Publishing Ltd Aviation Forums


Good on them

[brooksjg]

Some perspective on this. The only incident where there is no indication the crew knew about the ash at the time is

...

Can't believe we're quoting from the same document!!!

The one I'm looking at is
The 1991 Pinatubo Eruptions and Their Effects on Aircraft Operations by Thomas J. Casadevall,1 Perla J. Delos Reyes,2 and David J. Schneider3

In that report incident 91-09 is perhaps the best example of an undetected encounter with NO external evidence on the aircraft yet still severely trashed turbines. There are several others where no primary incident location is recorded, for several possible reasons. As the original authors state:

The detail of information was variable, especially concerning the locations of encounters and damage. In some cases, carriers were reluctant to discuss encounters, owing to concerns over possible future liability. In other cases, pilots may have been unaware that their aircraft had flown through an ash cloud, and damage to the aircraft might not have been noticed until the aircraft was later inspected on the ground. This partly explains why there are position data for only 11 of the incidents (fig. 1; table 1).

At this date, I doubt that anyone could say with any confidence which reason accounted for which piece of missing data in incidents in 1991!

BUT the key feature that is common to this AND the later NASA DC-8 incident north of Iceland AND probably some aspects of the Finnish F-16 Hornet ash incident two weeks ago is that there ARE many well-documented cases of significant turbine damage when the pilots were completely unaware of any ash encounter. You may not like these facts but unfortunately they are there in black and white, from multiple independent sources.

[Sunfish]

Concord:

It's a law of physics. You start to give ANY MASS a rotational velocity around a point then its going to move outwards.

Sorry but even if the forces are tiny and the movement is small the effect is still there.

However i'm not in a position to state without facts or figures if there would be any difference in ash density into the non-bypass airflow.

You are forgetting that between each row of blades in both Compressor and turbine there are stator blades whose job is to ensure that precisely what you think will happen (rotational motion) does NOT happen.

To put it another way, rotational motion in both Compressor and Turbine gas streams is wasted (rotational) energy.

[brooksjg]

Hmmm - I wish I'd never mentioned centripetal forces acting on ash particles in the first place!

Suffice it that an ash particle entering a high-bypass engine near the cicumference of the fan will DEFINITELY go down the bypass duct and cause no problem, a particle near the hub will DEFINITELY go into the core and might not emerge at the other end! Other particles at other points between hub and circumference will have varying chances of going 'through' or 'round' the hot section.

The point that even with a high bypass ratio, the core must still eat tons of air to get enough power to turn the fan is well taken.

Bottom line: only engine manufacturers can offer definitive numbers for the max ash particle density per cubic metre of intake air, taking account of everything that might happen to the air and the particles going through their turbine.

[infrequentflyer789]

Originally Posted by Intruder

There will always be second-guessers. The fact that there were no ash incidents gives clear evidence that the Eurocontrol policy was successful. There is no way to tell how many incidents or mishaps there would have been without the policy.

Yes there is, because the policy was changed from "no fly" to "fly" while the ash cloud was still there. Apparently even on the previous "zero tolerance" measures the asirspace would be open now, but there were, depending on who you believe, two, three or several days of flying through it. Say it was two days of flying through it, and six days of not:

• Total commercial jets (or any jets actually) that fell out of the sky in the six days not flying through the ash: none.
• Total commercial jets that fell out of the sky in the two days flying through the ash: none.
• Calculate total commercial jets that would have fallen out of the sky if same threshold had been applied across the six days: six * zero / two = none.

If you think that is over-simplistic, you might want to consider that allegedly (since it's the daily mail - although it appears a well written and researched article from what I do know) the measured ash concentration over the UK never got higher than 1/20 of the current "safe limit". See The ash cloud that never was: How volcanic plume over UK was only a twentieth of safe-flying limit and blunders led to lock-down | Mail Online


We live in an imperfect random world that is inherently not perfectly mesurable - zero tolerance policies are inherently dumb. Find any VA ? - have to close airspace. That's the easy part.

Now how do you reopen it ? How do you prove there is zero VA ? How many test flights over how many days (remembering you've just grounded your test aircraft for repainting, after the eruption started...) have to come up clean ? What if you didn't cover the whole area and missed some ash, what if your instruments aren't sensitive enough, how do you prove there is zero VA so you can re-open airspace ?

Answers on a postcard to the relevant authorities, they need your help because their previous plan looked like:

1. IF find VA THEN close airspace
2. Hope (1) never happens

[lomapaseo]

You are forgetting that between each row of blades in both Compressor and turbine there are stator blades whose job is to ensure that precisely what you think will happen (rotational motion) does NOT happen.

To put it another way, rotational motion in both Compressor and Turbine gas streams is wasted (rotational) energy.

Partly correct.

The rotational motion only lasts between the aft side of the spinning blade and the entrance to a stator row. However it is within that distance that the heavier particles will deflect outward. Very significant between the back of a fan blade and the inlet to the core.

I believe that there are some patents filed on this very basis (GE, Boeing, etc.)

[Intruder]

We live in an imperfect random world that is inherently not perfectly mesurable - zero tolerance policies are inherently dumb. Find any VA ? - have to close airspace. That's the easy part.

Now how do you reopen it ? How do you prove there is zero VA ? How many test flights over how many days (remembering you've just grounded your test aircraft for repainting, after the eruption started...) have to come up clean ? What if you didn't cover the whole area and missed some ash, what if your instruments aren't sensitive enough, how do you prove there is zero VA so you can re-open airspace ?

Since our world is so imperfect and random, we sometimes have to resort to the best information available when making decisions, even knowing that information is imperfect. The best information the government authorities had were the cloud models, which predicted significant ash over a wide area. When the lives of so many people and the reliability of so many engines is at stake, there is no sane choice but to be conservative IF, as is proclaimed by all the regulators AND the airlines, "Safety is Paramount" is indeed the truth. Personally, I applaud those regulators for deciding it is time to do more than pay lip service to safety concerns that happen to have significant cost and corporate and personal inconvenience.

How many of those airlines would have accepted strict liability for any damage and/or injury caused by ash ingestion? I suspect not one.

[Pace]

Intruder

I am glad you have the complete confidence in the "experts" The trouble with that is that everyone has their own interests their own backs to watch their own agenda.

Zero ash tolerance was abandoned in a matter of days for plucked out of the sky percentage ash? More like sock it and see?

Even the new limits are riddled and based on a fairly constant level of ash over a large distance. Where are those samples taken and what happens in the areas not taken? You may get a suitable level in one area which fits within the limits but half a mile away a much denser area which has been completely missed.

In the Alaskan eruption Ash circulated the globe three times before completely dissipating. 1000s of aircraft probably penetrated low density ash ridden air without even knowing about it. Maybe what the eye doesnt see the heart doesnt grieve?

The pilot as in any situation is best placed to determine whether a flight is safe or not. Not some politician or Quango leader who has no aviation experience whatsover and is more intent on watching his/ her back or lining his or her colleagues hands in gold.

As in any other atmosphere threat whether thunderstorms, bird strikes, strong winds, fog etc the pilot has the data but makes the decisions.
More aircraft have been downed by thunderstorms, More aircraft downed by fog, more aircraft downed by in flight turbulence and windshear, more aircraft downed by bird strikes, more downed by strong crosswinds, more by ice than ever in diffused ash.

Yes those pilots fly within minima and regulations but they fly.
Why is ash any different?
If we never flew because of a potentail threat albeit how small the skies would have been empty a long time ago.

Pace

[peter we]

The pilot as in any situation is best placed to determine whether a flight is safe or not. Not some politician or Quango leader who has no aviation experience whatsover and is more intent on watching his/ her back or lining his or her colleagues hands in gold.

I'd be interested in your attitude to the effects of VA on the medium term safety of the aircraft. That is, in a few weeks time when you are not aboard but the effect of your decision is going to affect the reliability of the aircraft.

Or the affect on profitability over the longer term that results in UK/European aircraft not being economical to run due to VA damage?

(Not that any of this seems to have surfaced so far and it's academic as we have taken the decision to run the experiment).

[foxfire42]

In the Alaskan eruption Ash circulated the globe three times before completely dissipating.

I'm pretty sure that was the St Helens volcano that did that. I'm also fairly sure that much of the ash that circled the globe was at altitudes >65,000 ft (see section on Plinian Column), which should have kept it out of reach of most planes.

[captainpaddy]

Pace, you really do have a point. If the end of the world was nigh and volcanoes were active all over the place, you can be very sure we would all be flying around in whatever came out of them because that would be the only way an acceptable level of operations could continue. Regulations would be tightened up and the risk mitigated as much as possible. All the phenomena you mention are just like that - too widespread and frequent for simple avoidance to be a realistic option. Personally I don't think ash falls into this category but:

If I thought that what we had just done was exactly that - carefully worked out the real risk and the likely result of an increase in exposure both in the shorter and longer term, then I feel none of us could really take issue with it. That is just what has happened with so many other threats. But the difference here is through a misjudgement by the industry we never bothered to look into it in any great detail. Suddenly we were caught out and the pressure was on for a quick decision.

My only question to you would be how can you be happy with the way the new procedures were created? 2 days is an absolutely incredibly short time for so many sections of the industry to come up with an answer. And in particular how can you be happy with it in the light of the fact that test flights, military flights and civilian flights, have appeared to have continued to suffer problems that the new regulations said would not occur?

Genuinely, I would like to know what you think. Maybe you have some other nugget that might make me see this whole thing differently....

[Pace]

If I thought that what we had just done was exactly that - carefully worked out the real risk and the likely result of an increase in exposure both in the shorter and longer term, then I feel none of us could really take issue with it. That is just what has happened with so many other threats. But the difference here is through a misjudgement by the industry we never bothered to look into it in any great detail. Suddenly we were caught out and the pressure was on for a quick decision.

My only question to you would be how can you be happy with the way the new procedures were created? 2 days is an absolutely incredibly short time for so many sections of the industry to come up with an answer. And in particular how can you be happy with it in the light of the fact that test flights, military flights and civilian flights, have appeared to have continued to suffer problems that the new regulations said would not occur?

Genuinely, I would like to know what you think. Maybe you have some other nugget that might make me see this whole thing differently....

CaptainPaddy

On this part I cannot disagree with you. In areas of known ash I would limit operations to daylight only where pilots will have a better chance of seeing denser areas of ash and avoid.

My instincts (and that is all they are) is that if you can see it the ash clouds, mist etc MAY do harm. If you cannot see the ash clouds mist in daylight VMC in all probability there will be no harm.

It is important to differentiate between two types of harm. Harm that could down an aircraft and cause loss of life and harm that would shorten engine life.

The very diffused ash in all probability MAY shorten engine life but that becomes the bill payers problem.

I totally agree that it is more than likely that the new limits were picked out of a hat but apart from having a long and detailed analysis the new limits are a starting point.

Even with a long detailed analysis and testing we never really know what is what until tested in the field. I know car manufacturers can drive thousands of miles in testing conditions and only discover problems when the cars are on the road in daily use.

There are threats in the air that we live with and accept every day which have and do bring down aircraft. To date even dense ash has not killed anyone (unless your a smoker Is the ash threat bigger or mainly a media driven hype?
NO!!! in low density ash its more likely to cost in the pocket rather than lives.
I am afraid till something happens to prove otherwise.

Pace

[captainpaddy]

Well, seeing as the decision has already been made there is probably little point in me occupying the dark side anymore. I gues ultimately your right. Engine monitoring programs will have to carefully watched over the next few months. They should be enough to prevent any catastrophic issues.

Isn't a shame and in my mind very damning of this industry, that we need to rely on a previously instated and successful safety measure to protect us from the potential ill effects of brand new "safety" measure?

But there lies the truth about the world we work in. The there have been many cases over the years of regulators bending to the demands of the industry. September 11th infuriated me as a light aircraft pilot in the US. Commercial airliners knocked down two buildings. Every single aircraft is grounded. Two days later commercial traffic is flying again and it takes two full weeks before light aircraft are allowed up. Many small businesses collapse as a result. How could light aircraft be a greater threat than an airliner? Wel,, they're not. The just can't lobby as effectively. I think we have just witnessed something similar again....

Thanks for the reply Pace.