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Ash clouds threaten air traffic

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Ash clouds threaten air traffic

Old 21st Apr 2010, 08:42
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Irish Aviation Authority - Document Details
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Old 21st Apr 2010, 08:44
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LOL...

The CAA/NATS would I'm sure have preferred to say something along the lines of "there's ash out there guys'n'gals, check the VAAC as to where it is forecast to be, launch at your discretion", however I'll bet the operators took the view "we're only going if you say its safe to go and if it turns out it wasn't safe then we're coming after you"; the blood-sucking lawyers will have had a field day sorting out where the responsibility rests in the event of some poor sod turning their 747 into a lawn dart.

The whole thing was an exercise in ass covering in the event of an incident. I suspect the operators could've had unrestricted movement from the outset if they'd stated that they wished to continue operating normally, and would accept 100% responsibility for the safe operation of flights through airspace forecast to be contaminated with ash. However, it would appear that they didn't, and (some) are only too quick to start pointing fingers elsewhere. A case of wanting to have one's cake and eat it me thinks.

Wonder how WW will feel two days hence if half his fleet is grounded because of silica contamination of fan blades...
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Old 21st Apr 2010, 08:47
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DespairingTraveller:

Very well put, especially para 2c.

Interesting to see how all these 'procedural deficiencies' will be corrected (or tucked back beneath the carpet).
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Old 21st Apr 2010, 08:47
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Considering the unprecedented nature of this event, the fact that we, most certainly, had to suspend operations in the first two or three days after the ash reached the UK. I think everyone has done well to find a way through the problem and get airborne again in the time we have. The Met Office/VAAC did their job, NATS did what any ATS should have done and the operators stopped flying in the face of a known risk. There will surely be lessons to be learned and we must understand this event in detail.

It will now be interesting to see what happens should we have another ash cloud heading this way.

Despairing Traveller,

It is perhaps true that we have lessons to be learned from this event, which is by no means over in my opinion. In the history of aviation we have continually learned from our mistakes, we investigate our acccidents in detail and have developed procedures to ensure we operate as safely as we can. It is instinctive for us to stop operations when faced with risks we don't fully understand or can't avoid, such was the case in this event. And I believe most would not want it any other way. Economic pressures come second to the safety of passengers and crew- the industry and regulators have now evaluated the risk, found a way to ensure your safety- operations commence.

Last edited by no sig; 21st Apr 2010 at 09:24.
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Old 21st Apr 2010, 08:54
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Thanks for the link. It has been saved!
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Old 21st Apr 2010, 09:02
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The CAA/NATS would I'm sure have preferred to say something along the lines of "there's ash out there guys'n'gals, check the VAAC as to where it is forecast to be, launch at your discretion", however I'll bet the operators took the view "we're only going if you say its safe to go and if it turns out it wasn't safe then we're coming after you"; the blood-sucking lawyers will have had a field day sorting out where the responsibility rests in the event of some poor sod turning their 747 into a lawn dart.
The CAA have basically said that; the risk is entirely with the operators.

If you read the Guardian article, its explains that the airlines have refused to set a safe operating level precisely becuase that exposes them to liability if things go wrong.

Why airlines resisted setting safe dust level for flights ? until now | World news | The Guardian
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Old 21st Apr 2010, 09:09
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Have BA or any other airline comfirmed that none of their engines have been affected by ash yet after landing in the UK last night?

Just wondering how long it takes to check? Also curious as to why there has been silence and WW has not confirmed all was ok?
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Old 21st Apr 2010, 09:11
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From The Guardian

Last night's reopening of the skies over the UK followed intense lobbying from an airline industry that for years has resisted efforts by regulators to set a "safe" level of volcanic ash at which it is considered that flights can continue, the Guardian can reveal.

What airlines had been afraid of was the potential damage to their reputation and finances in the event of one of their planes being lost due to dust after an all-clear had been announced, with a fear of legal actions arising from the deaths of all those who had been on board.

Unwillingness to grasp this nettle hampered what had been continuing discussions on the dust issue prior to the Eyjafjallajokull volcano erupting.

However, faced with losses running into hundreds of millions as the effect of Eyjafjallajokull spread and lingered into a sixth day, it was the airlines who began to call for the regulators to determine and set such a safe threshold, to avert the severe financial consequences of planes idle across Europe and passengers claiming refunds for cancelled journeys.
A source at the International Civil Aviation Organisation (ICAO) said of the history of the failure of efforts to agree a safe level: "The bottom line is that there is a huge liability issue for the industry here, so they have been super cautious on providing information. If they say it is safe, and there is an accident, they will get slaughtered."

The organisation has been trying since at least 2008 to get airlines and manufacturers to help establish a consensus on a safe concentration of volcanic ash.

In an indication of the pressure now put on air safety bodies, British Airways said hours before the UK's flights resumed that it hoped the UK's Civil Aviation Authority now had all the data necessary to lift the flight ban. Pointedly referring to the relaxation of restrictions by states such as Italy and the Netherlands, BA had said: "Despite the fact that airspace over most European countries is open, UK airspace remains effectively closed. We hope that on the basis of the data provided by the industry, the CAA will be in a position to direct National Air Traffic Services (Nats) to reopen UK airspace."

Airline sources said that a meeting this morning between the CAA, Nats, airline executives and the transport secretary, Lord Adonis, was "constructive" as safe flight corridors through the ash were discussed.
This week BA, easyJet and Virgin Atlantic have demanded a greater say in decisions on flight bans and air safety.

The perceived inconsistency of various European states' approaches to the volcano cloud has been one of the biggest complaints from airlines.
Ryanair, Europe's largest short-haul carrier, became the latest to reveal the scale of its losses, £5m a day, while the Emirates airline of Dubai warned of an "implosion" if restrictions were not lifted.

"Unless the states ... come in and bail these companies out, there won't be many carriers left," said Tim Clark, Emirates president. "You simply can't afford to shut down something the size of Europe."

Asked on BBC Newsnight about how much pressure the government had come under to lift the flight ban, Adonis said "They've obviously wanted to be able to fly their planes - of course they have - but that has not been the issue … the issue is the assessment of the safety authorities as to what is the safe way in which planes can fly when there is a presence of ash.

"The fact which has changed in the last week is we have had a volcanic eruption, and having to assess safe levels of ash within which planes can fly has been an urgent issue which the safety authorities have had to deal with. That's been what's changed over the last five days - it's not been pressure from the industry which has caused [it]."

The crucial change came when Nats announced that safety tests had shown aero engines "had increased tolerance levels in low ash density levels".

Nats spokesman Alex Bristol told Sky News: "We don't feel we have been under pressure from the government. Where the pressure has come has been to better understand the safety implications. Our first priority has been safety, and the reason we didn't simply lift the restrictions was because of our desire for safety."

According to the International Air Transport Association (Iata), the crisis had cost carriers $200m (£130m) a day – most of it for European operators. A group of those airlines, including the association of budget airlines, urged the European Union to waive consumer legislation which imposes costs, including hotels for stranded passengers, during prolonged disruption; it was turning "a crisis into an economic catastrophe".

Going back into the history of attempts to set a safe level of ash, minutes of a Paris meeting in 2008 show the industry at odds with regulators. The ICAO meeting concluded that improved measurement techniques should allow progress "with regard to the definition of the lower limit on safe ash concentrations".

The ICAO complained it had "proven difficult to get formal aviation representation" at workshops on the issue organised by the UN's World Meteorological Organisation. It suggested "input of the aviation industry to this problem may have to be sought" through its sub-group on volcanoes, which has industry representatives. It asked several groups, including the International Air Transport Association, Iata, representing 230 airlines, to prepare reports for the volcano group's next meeting at Lima in Peru last month.

Minutes for that meeting show the industry did not deliver. "Iata informed the group about the strong efforts made in order to get representation from the industry ... but unfortunately these efforts had not been successful, to the disappointment of the group."

Herbert Puempel, chief of the WMO aeronautical meteorology division, who sits on the ICAO group, said the industry's reluctance was "fully understandable". "They have found it very difficult to come back with a single answer. If they have one number then it would be very low," he said. "The moment you set a limit then the lawyers will have a field day."
Iata said: "At the end of the day we are dependent on the airframe and engine manufacturers and their experts. We have encouraged them to participate." However, an aerospace industry source told the Guardian that any attempt to blame aircraft and engine makers was "passing the buck".
Perhaps I wasn't too far off the mark then...
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Old 21st Apr 2010, 09:24
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After flight inspections

Glad to be back flying, but haven't seen much discussion of this inspection requirement.
Surprised to see nothing on this in the Engs & Techs forum.
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Old 21st Apr 2010, 09:51
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Has anyone any actual evidence of the Met Office being wrong? As in, ash turning up where it shouldn't be or no ash being where the ash was forecast?

I'm repeatedly amazed by some of the denialism on this thread, especially as people have been posting Meteosat and MODIS imagery of it since the word go. As I say, it just seems to be a sort of sub-culture of harrumphing about the Met Office (and Harriet Harman, God knows why).
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Old 21st Apr 2010, 09:55
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Perhaps I wasn't too far off the mark then..
There is a legal requirement that companies assess potential risks to their business and demonstrate that they have take steps to mitigate it. Auditors will not sign off a companies accounts if there is not contingency plan in place - its to protect shareholders.

How much credibility is there in the claim that the possibility of an Icelandic volcano shutting down EU airspace was an unforeseen event?

None. It wasn't just a possibility, it was an absolute certainty to happen eventually.
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Old 21st Apr 2010, 09:59
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How much credibility is there in the claim that the possibility of an Icelandic volcano shutting down EU airspace was an unforeseen event?
Given the existence of the EUR Region Volcanic Ash Contingency Plan (which uses Katla in its examples !) , what do you think the answer to that question is ?
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Old 21st Apr 2010, 10:04
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Originally Posted by Re-Heat
Which airline do you fly for again? I'll make a note to avoid paxing on it. I assume you also ignore the faceless bureaucrats who forecast storm cells as well, right?
Personally, I'd rather have the pilots looking where the storm cells actually are than relying on some "forecast" from a bureaucrat. Particularly if the forecast is from a computer model at the "barbeque summer" office.

I have far more trust in those actually flying the plane than those supposedly in charge who take several days to organise a meeting to talk about maybe having a european strategy.

[ I spent 24+hrs on a coach with wife and kids - not pleasant but we got back, not the end of the world. However, I would have also taken the captains decision to fly, like we always do with every MEL etc. - most of which decisions we never even hear about sat in the back. ]
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Old 21st Apr 2010, 10:12
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German airspace is opened for IFR flights / no more restrictions from 11:00 hrs


21/04/10 - Due to the current development of the weather situation, German airspace can be opened for flights according to instrument flight rules (IFR flights). The decision of DFS is based on the current information of the German meteorological service (DWD). According to this information, airspace contamination has significantly decreased and will continue to decrease owing to the weather conditions.

IFR flights can currently be conducted at the international airports of Hamburg, Bremen, Hannover, Berlin-Tegel, Berlin-Schönefeld, Cologne/Bonn, Frankfurt, Saarbrücken, Nürnberg, Stuttgart and Munich. The same applies to the regional airport Frankfurt-Hahn. At 11:00 hrs, all other airports will also be opened for IFR traffic. This means that from 11:00 hrs, there will be no more restrictions on IFR traffic in Germany.

Updated on: 21/4, 10:15 hrs
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Old 21st Apr 2010, 10:20
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re 2166 - I will be outraged if the industry is bailed out by the tax payer. The people left unfairly out of pocket will be the traveling public who have been left to fend for themselves in all of this. The industry has turned a blind eye to this possible problem bescause it suited them to do so and now they are going to try and blame everybody else when it has back fired on them.
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Old 21st Apr 2010, 10:21
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Originally Posted by steamchicken
Has anyone any actual evidence of the Met Office being wrong? As in, ash turning up where it shouldn't be or no ash being where the ash was forecast?
Increasing disagreements between model and actual sat imagery. Different affected area maps from Met Office and Eurocontrol (at least one of them has to have been wrong). More info / rumour to this effect in previous posts on this thread eg. this one: http://www.pprune.org/rumours-news/412103-ash-clouds-threaten-air-traffic-108.html#post5649483
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Old 21st Apr 2010, 10:21
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Someone was asking for mass-flow numbers earlier on. RR's Web site gives an intake mass-flow for the RB211-535E4B (I picked an engine arbitrarily) of 1,177lb/sec or 533.87kg/sec.

Based on the figure of 0.3 milligrams per m3 given for Stranraer, at an air density of 1.2kg/m3 at sea level (obviously we're not interested in sea level, but at least it's wrong in a known way - the ash measurement is a sea-level one and I guess RR's figures are test-stand measurements, so it's consistent) that would be 444m3 of air a second and 0.133g of ash a second - 478g of ash per engine-hour.

(Although, the -535 is a very high bypass turbofan, so perhaps we need the core mass flow...)
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Old 21st Apr 2010, 10:24
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Let the Great Experiment begin...

Let the Great Experiment begin: Science will reign supreme against the detritus of more primitive gods, and tens of thousands of passengers will be as guinea pigs to prove as self-evident the safety of airline profitability and political power...

New London VAAC NWP Volcanic Ash Concentration Charts rely on so-called "standard threshold" - anyone know what this is?

According to CAA statement of 20 April: "Our way forward is based on international data and evidence from previous volcanic ash incidents, new data collected from test flights and additional analysis from manufacturers over the past few days."

Anyone know where materials of these data and analysis are located?
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Old 21st Apr 2010, 10:37
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The 1991 Pinatubo eruptions and their effects on aircraft operations

Found this 21pg public domain document from the USGS

There's extensive detail and information as well about aircraft incidents - just some excerpts below

The 1991 Pinatubo eruptions and their effects on aircraft operations - Documents & Publications - Professional Resources - PreventionWeb.net


The 1991 Pinatubo Eruptions and Their Effects on Aircraft Operations
By Thomas J. Casadevall,1 Perla J. Delos Reyes,2 and David J. Schneider3
1
U.S. Geological Survey.
2
Philippine Institute of Volcanology and Seismology, Quezon City, Philippines.
3
Michigan Technological University, Department of Geological Engineering, Houghton, MI 49931.


ABSTRACT
The explosive eruptions of Mount Pinatubo in June 1991 injected enormous clouds of volcanic ash and acid gases into the stratosphere to altitudes in excess of 100,000 feet. The largest ash cloud, from the June 15 eruption, was carried by upper level winds to the west and circled the globe in 22 days. The June 15 cloud spread laterally to cover a broad equatorial band from about 10°S. to 20° N. latitude and contaminated some of the world's busiest air traffic corridors. Sixteen damaging encounters were
reported between jet aircraft and the drifting ash clouds from the June 12 and 15, 1991, eruptions. Three encounters occurred within 200 kilometers from the volcano with ash clouds less than 3 hours
old. Twelve encounters occurred over Southeast Asia at distances of 720 to 1,740 kilometers west from the volcano when the ash cloud was between 12 and 24 hours old. Encounters with the Pinatubo ash cloud caused in-flight loss of power to one engine on each of two different aircraft. A total of 10 engines were damaged and replaced, including all four engines on a single jumbo jet.

Following the 1991 eruptions, longer term damage to aircraft and engines related to volcanogenic SO2 gas has been documented including crazing of acrylic airplane windows, premature fading of polyurethane paint on jetliners, and accumulation of sulfate deposits in engines. Ash fall in the Philippines damaged aircraft on the ground and caused seven airports to close.

Restoration of airport operations presented unique challenges, which were successfully met by officials at Manila International Airport and at Cubi Point Naval Air Station, Subic Bay. Lessons
learned in these clean-up operations have broad applicability worldwide.

Between April 12 and June 9, 1991, Philippine aviation authorities issued at least eight aeronautical information notices about the preeruption restless state of Mount Pinatubo. The large number of
aircraft affected by the Pinatubo ash clouds indicates that this information either did not reach appropriate officials or that the pilots, air traffic controllers, and flight dispatchers who received this information were not sufficiently educated about the volcanic ash hazard to know what to do with the information.

INTRODUCTION
Jet aircraft are damaged when they fly through clouds containing finely fragmented rock debris and acid gases produced by explosive volcanic eruptions (Casadevall, 1992). Clouds of volcanic ash and corrosive gases cannot be detected by weather radar currently carried aboard airplanes, and such clouds are difficult to distinguish visually from meteorological clouds. In the past 15 years, there have been more than 80 in-flight encounters between volcanic ash clouds and commercial jet aircraft.

The explosive eruptions of Mount Pinatubo volcano in the Philippines in June 1991 injected enormous clouds of volcanic ash and gases into the stratosphere to altitudes in excess of 100,000 ft. Within several days of the June eruptions, at least 16 commercial jet airplanes had been damaged by in-flight encounters with the drifting ash clouds from Pinatubo. Closer to the volcano, ash fall in the Philippines damaged about two dozen aircraft on the ground and affected seven airports. This report describes the effects of the 1991 Pinatubo eruptions on aircraft and airports, seeks to understand why so many encounters occurred, and reviews the solutions to the ash-cloud hazard reached by Philippine
authorities.

Incident number Date Time (G.m.t.)1 Location Latitude Longitude Altitude (feet) Aircraft type Comments
91-01 6/12/91 0420 170 km from volcano; 60 nautical miles from LUBANG along air route B460.
14°00' 119°30' 37,000 747-300


During a 3-min encounter with volcanic ash, crew experienced thin haze inside aircraft that smelled like a burning electrical wire. Aircraft landed safely at Manila Airport. Aircraft and engines were inspected and serviced at Manila in accordance with recommended procedures. When aircraft attempted to depart, its four engines had a strong vibration, and aircraft was grounded at Manila for detailed maintenance and replacement of all four engines.


91-02 6/12/91 uk 720 km west of volcano on route from Singapore to Tokyo.
13°50' 113°50' 37,000 747-400


No significant damage to aircraft when inspected
on ground in Tokyo.


91-03 6/12/91 1630 Approx. 1,000 km from volcano; between way points
ADPIM and 11°10' 112°10' 33,000 DC-10
series 40 Flight from Kuala Lumpur to Tokyo;


observed a discharge phenomena on windshield for 20 min. Ground inspection at
Narita revealed no LAVEN. damage. Encounters 3 and 11 involved same aircraft.


91-04 6/15/91 1740 Approx. 1,150 km from volcano; between way points
SUKAR and CAVOI. 13°10' 110°50' 29,000 747-400


Aircraft encountered ash cloud at 29,000 ft at approximately 600 nm west of volcano. Crew observed St. Elmo's fire on the windshield and a scent similar to an
electrical fire in the cockpit for 6 to 8 min as they went through the ash. There was no abnormal indication in the cockpit. The crew observed a green echo, which seemed to be ash on weather radar, but it disappeared when they
were clear of the ash. Flight attendants reported thin (whitish) fog in the cabin, most dense in the upper deck compartment, followed by the forward cabin. The flight was continued to Tokyo, where engine inspection revealed that all four
engines were damaged and were replaced. First- stage nozzle guide vane cooling air holes were 70-80% blocked. Other damage occurred to the cockpit windows, cabin windows, Pitot static probes, landing light covers, navigation lights,
and all leading edge areas.


91-05 6/15/91 1547 Over Vietnam on route from Hong Kong
to Singapore; in Bangkok FIR.
13°00' 108°00' uk 747-SP

Ash and sulfur odor, electrostatic discharge, blue-green light over
Vietnam. Ground inspection revealed no significant damage, and
aircraft continued in service.



91-06 6/15/91 uk uk uk uk uk 747-200

freighter Aircraft flew through "heavy volcanic ash." Cockpit and cabin areas
were contaminated with volcanic ash. No additional information
available.


91-07 6/15/91 uk Route between Tokyo and Singapore.
uk uk 35,000 747-251


Flight from Narita to Singapore was rerouted to Manila due to weather
in Singapore area. En route to Manila, encountered volcanic ash
cloud at 35,000 ft for approximately 12 min and was then diverted to
Taipei. Engines set at cruise. Sparks were noted coming from windows
and Crew reported hearing ash hit the aircraft. EGT for all four engines rose 40-50°C and started to fluctuate. One hour later all EGTs were
back to normal. Ground inspection in Taipei revealed no significant
damage to exterior or to engines. Aircraft continued in service.


91-08 6/15/91 uk <200 km from volcano; on
approach to Manila from south.
uk uk uk DC-10
series 30

Flight from Sydney to Manila encountered ash on approach to Manila from south. Engines set at low power but found to contain "lots of ash" when inspected after landing. Exterior abrasion visible, including engine cowls.


91-09 6/15/91 uk Route between Singapore
and Osaka. uk uk uk 747-300


Aircraft was in ash cloud for 29 min while en route from Singapore to Osaka. Date of encounter uncertain, probably 6/15; one report indicates 6/19.
Inspection of aircraft exterior showed no significant damage.
Engines #1 and #4 were replaced; "90% of the first-stage turbine blades
have bullseyes on the airfoil's mid-span pressure side and some first-stage vane leading edge ash buildup at 3 o'clock position."


91-11 6/15/91 1730 Approx. 1,050
km from 15°15' 110°30' 29,000 DC-10 series 40


Flight from Kuala Lumpur to Tokyo; volcano; between way points SUKAR
and CAVOI, 120 nautical miles from CAVOI. observed a discharge
phenomena on windshield for 25 min. Ground inspection at Narita revealed no damage. Encounters 3 and 11 involved same aircraft.


91-12 6/15/91 1910 Approx. 1,050
km from volcano; between way points SUKAR and CAVOI,
120 nautical miles from CAVOI.
15°15' 110°30' 29,000 DC-10
series 40


Flight from Singapore to Osaka; crew
observed a discharge phenomena on
windshield for 30 min. Ground inspection at
Narita revealed no damage.


91-13 6/15/91 0910 Approx. 100
km from volcano; flight from Manila to
Hong Kong. uk uk uk 747-428

After takeoff from Manila, airplane skirted a volcanic ash cloud.
On the ground in Hong Kong, black marks were noted on the exterior of the left wing. Engines were borescoped and no discrepancies were found. Airplane continued to Delhi. Preparing to leave Delhi, unable to start engine #1. Fuel pump was replaced and additional inspections of airplane revealed no damage. Airplane continued to Paris.



91-14 6/16/91 uk Route between Kuala Lumpur and Kota Kinabalu.
uk uk uk 737-200


freighter 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.


91-15 6/17/91
(?) uk Flight likely on Tokyo to
Singapore uk uk uk DC-10


Airplane reportedly encountered ash from
Pinatubo on June 17. #3 route. engine was reported to have been shut down in flight; ash encounter may have caused in- flight shutdown. Inspection of engines revealed "heavy deposits" of what was presumed to be volcanic ash. No information about flight route, encounter duration, and such.


91-16 6/17/91 0412 930 km from volcano; 50 nautical miles
east of way point IDOSI on route A901.
19°30' 112°40' 37,000 747-200B


Flight from Johannesburg to Taipei via Mauritius.
Encounter occurred at 37,000 ft 50 nm east of way point IDOSI on
route A901; entered a cloud at 0412 G.m.t.; temperature increased
from -48°C to -37°C in 2 min; aircraft descended to 29,000 ft and landed at 0540 G.m.t.; engine #1 surged and was shut down; engine #4 lost power; descended to 29,000 ft to restart #1. Aircraft landed safely at Taipei. Service
terminated. Engine #1 replaced and aircraft returned to South Africa on 6/21 for further inspection.



91-17 6/15/91 na Aircraft on ground at
Manila International Airport. 14°30' 121°00'

On ground L-1011 Maintenance crew attempted to remove
volcanic ash from window by using wiper blades. Resulted in abrasion of windows, which required replacement.




DAMAGE
When a jetliner flying in excess of 400 knots (740 km/h) enters a cloud of finely fragmented rock particles, the principal damage will be abrasion of the exterior, forward-facing surfaces and
accumulation of ash into surface openings (Casadevall, 1992). An example of the exterior damage to one jumbo jet after an encounter with a Pinatubo ash cloud is shown schematically in figure 7. Ingestion of ash into the engines will cause abrasion damage, especially to compressor fan blades. Because jet engines operate at temperatures in excess of 700°C, melting of ash and accumulation of this ash in the turbine section is an important problem as well (Przedpelski and Casadevall, 1994).
Remelted ash may block the passage of air through the engines and cause the engine to stop. In an least
one airplane (incident 91-04 in table 1), first-stage nozzle guide vane cooling holes were 70 to 80 percent blocked.
Figure 7. Damage to exterior surfaces of a 747-400 jumbo jet following an encounter with the June 15,
1991, ash cloud from Mount Pinatubo.

The majority of the Pinatubo encounters occurred at distances of up to 2,000 km from the volcano with an ash cloud that was at least 12 h old. The aging of the ash cloud allowed the coarser ash to settle from the cloud and prevented some of the more severe damage such as that which occurred to jumbo-
jet aircraft from earlier encounters with volcanic ash (Smith, 1983; Tootell, 1985; and Casadevall,
1994). In the Pinatubo case, there were few reports of abrasion of forward-facing cabin windows, so it is suggested that particles larger than about 30 m in diameter had already settled from the cloud. Particles smaller than this diameter are efficiently swept over the window surface by the slipstream and do not impact the window surface (Pieri and Oeding, 1991).

Longer term damage related primarily to the SO2 gas and sulfuric acid aerosols produced by the eruption (Self and others, this volume) did not become apparent until months after the eruption. Some Asian-based carriers noted that jet engines on their airplanes have accumulated deposits of sulfate minerals such as anhydrite and gypsum in the turbine. This material blocked cooling holes in the first- stage nozzle guide vane at the inlet to the turbine section of the engine and thereby interfered with the cooling of the turbine. As a result, engines overheated. The sulfate deposits found in the turbine section appear to be related to ingestion and oxidation of SO2 and sulfuric acid aerosols that originated
in the Pinatubo eruption clouds of June 15 (Casadevall and Rye, 1994).

Additional problems related to the acidic aerosols include the increased incidence of crazing of acrylic windows (Berner, 1993) and fading of polyurethane paint on jetliners (T.M. Murray, Boeing, written commun., 1993). Unlike the circumstances involving in-flight encounters with the ash clouds, which
were largely restricted to the region west of the volcano, the gas cloud from Pinatubo has been widely dispersed throughout the Northern Hemisphere and has thereby affected aircraft that fly in this airspace. A similar increase in the incidence of window crazing was observed for several years following the
eruptions of El Chichón Volcano in 1982 (Rogers, 1984; 1985; Bernard and Rose, 1990). Pinatubo erupted nearly 3 times more SO2 than did El Chichón (Bluth and others, 1992). Thus, the types of problems related to volcanogenic sulfur gas and sulfuric acid aerosols may be expected to persist longer following the Pinatubo activity than after El Chichón.


LONG-TERM DAMAGE
In addition to the aircraft damage that was immediately evident in the days following the June 15 eruption, damage related primarily to SO2 gas has been reported by some airline companies and
manufacturers. One year after the eruption, in June 1992, there was an incident involving loss of engine power on a jumbo jet owing to accumulation of sulfate deposits in jet engines. Isotopic studies of these deposits suggest that the sulfate is derived from the ingestion and oxidation of SO2 and
sulfuric acid aerosols that originated in the Pinatubo eruption cloud of June 15 (Casadevall and Rye, 1994). Related problems recognized in 1992 such as the increased incidence of crazing of acrylic windows (Berner, 1993) and fading of polyurethane paint on jetliners are also due to volcanogenic sulfuric acid droplets in the atmosphere. Frequent inspections of aircraft should reveal any corrosion problems due to volcanogenic sulfur gases.

Last edited by STC-8; 21st Apr 2010 at 12:43. Reason: improve spacing/readability/additional aircraft incidents
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