Volcanic Ash, an awesome danger

Despite the great beauty of many things found in nature, some also present a great danger to mankinds’ activities. The unprecedented closure of so much of Europe’s airspace highlights the problems caused by volcanic ash. This is not just an issue for airlines and the travelling public, but also affects the whole economy and all those industries that rely on air transport.

I am now retired, but with many friends knowing that I worked in aviation, I have been asked over and over again what the fuss is all about. So, I have trawled a number of aviation and science websites and have put together the following layman’s guide. Back in 1982, when I was the Flight Training Manager of the British Airways 747 Fleet, one of our Boeing 747-236 aircraft flew into a volcanic ash cloud over Indonesia. The incident occurred at night, the crew couldn’t see the ash cloud either visually or on the radar, and the forecast had given virtually no information. At that time the aviation industry knew relatively little about the effects of volcanic ash on jet engines. The crew did a magnificent job after all 4 engines stopped and managed to get back on the ground at Jakarta. Wikepedia has a good account of what happened here.

Since then a lot of work has been done by the engine and airframe manufacturers, by airlines and by research organisations but the problem we still face is that no-one knows the exact density of ash which constitutes a danger, and neither can we track it accurately enough. We know that flying into a dense ash cloud causes major damage, discovered by the BA 747 over Indonesia in June 1982, and three weeks later by a Singapore Airlines 747 which lost three engines and had to make an emergency landing. We know that we can fly around the ash cloud if we can see it visually, but aircraft radars are not designed to detect ash, only water droplets in order to avoid thunderstorms. There have been other incidents since. For example, in December 1989, a KLM 747-400 flew into the ash cloud from Mt Redoubt in Alaska while descending towards Anchorage. All 4 engines flamed out, and the  crew had to work frantically to restart them, while at the same time having to cope with multiple electrical power failures as the systems changed back and forth between main generators and standby power which powers only a very limited set of essential services. There is a good description of what is involved in the North Pacific area in The US Geological Survey Fact Sheet 030-97.
Even fully equipped research aircraft can experience inadvertent encounters with Volcanic ash. A NASA DC-8, a highly instrumented research platform for conducting atmospheric science research, inadvertently flew into a diffuse volcanic ash cloud in February 2000 while on a flight from Edwards Air Force Base to Sweden. You can find details here. The encounter was in total darkness well north of Mt Hekla in Iceland. The aircraft was in the ash cloud for only 7 mins, yet considerable damage was done to all 4 engine, with the repairs to the engines alone costing $3.2 million. It was also estimated that the engines would only have been good for another 100hrs of service. I have seen reports (unverified) that the density of the ash over parts of Europe was at least 5 times as dense as the cloud penetrated by this DC-8.
When it comes to determining the density of the ash cloud over Europe it is important to realise that there are relatively few suitably equipped research aircraft that could investigate it, therefore considerable reliance has had to be placed on limited sampling, on forecasts of upper and lower level winds and on computer modelling. Clearly, following the events of the last week there is a need for more widescale research flights to find out exactly where and how dense such ash clouds really are. I know the Germans have flown some research flights but do I not know the results. Also several airlines (e.g. BA, DLH, AF, KLM and SAS) have flown a number of ‘test flights’, as has Airbus. But even if the results of these airline ‘test flights’ show no apparent adverse effects, we still do not know what longer term problems might occur, such as reduced engine life and/or reliability. By flying too soon it is just possible that a lot of expensive engine overhauls might suddenly be required which would not only cost money but stretch the available maintenance resources. On the other hand the airlines are losing vast amounts of money when they can ill afford to do so, as are the ancillary travel businesses, and as will those other industries which rely on ‘just-in-time’ delivery of components by air freight to keep their assembly lines going.

Caution is still necessary as there is so much more to learn. After the volcanic ash encounters in the 1980s, ICAO got all the experts together and agreed a number of precautions:- (1) the procedures to be adopted by the pilots if they encountered ash; (2) the maintenance inspections required to put the aircraft back into service; and (3), crucially, a worldwide International Airways Volcano Watch system with 9 Volcanic Ash Advisory Centres (VAACs) of which the London VAAC is one. The London VAAC is run by the UK Met Office which provides the necessary advisories to aviation. And I understand that in some recent ICAO meetings on the subject the experts and the airlines still cannot agree on a safe density level of ash.
From what I have read in the geology books there are various types of magma. Those with a low silicon content (silicon dioxide) produce lava with a low viscosity which flows relatively gently as seen in the volcanoes in the Hawaiian islands. And those with a higher silicon content which have a higher viscosity and tend to go bang like Mt St Helens. The Icelandic volcano would therefore seem to be a high silicon magma with the explosions intensified by coming into contact with the melted ice from the glacier. It also seems, by the same process to have produced a very high proportion of very fine particles which is why it is spreading so far and remaining suspended in the atmosphere, although of course this is not at all unusual.
Unfortunately for aviation these fine particles melt at around 1200degC and when they get into the combustion chambers of a jet engine they fuse onto the stators and turbine blades in the hot end of the engine. This alters the aerodynamic shape of the turbine blades causing the airflow to stall, the engine then surges and stops. Next, the dust is very fine and penetrates all the cooling ducts of the engine causing parts to overheat, especially the turbine blades. It also gets into the aircraft’s air conditioning system and all the electronics and ‘sand blasts’ the exterior, particularly the windscreen such that the pilots can’t see out. In the British Airways Flight 9 incident, they descended to around 13,000ft before they could get the engines to start again, and the captain had to land the aircraft looking out of the bottom left hand corner of his windscreen.
Turbine blades look like this, and they are very, very expensive! They are made of exotic alloys and have very small cooling ducts (around 0.25mm in diameter) to stop the blades melting in the hot gases coming from the combustion chambers. The ash blocks these ducts causing the blades to over-temperature, which in turn causes the blades to fail or need to be replaced.
The crew procedures, if the aircraft inadvertently flies into a volcanic ash cloud, consist basically of immediately reducing power to reduce the temperatures in the engines so as to avoid damage to the turbine blades and at the same time to reverse course to get out of the ash as quickly as possible. In airspace with a low density of air traffic this is not so a great problem, provided one has enough altitude and there are no mountains below. Airbus published a very good description of what is required and you can find it here. In busy European airspace, with so many routes closely spaced together, and with lots of aircraft at different altitudes, one can imagine the chaos that would ensue if a number of aircraft had to do this at the same time.
The engineering procedures before putting the aircraft back into service are also very onerous. All the engine manufacturer’s advice is explicit and similar:-
The following actions are recommended for engines that have been exposed but have been parked (not operated on the ground or in-flight) in a volcanic ash environment prior to the next engine start:
A. Remove volcanic ash from the area in front of engine inlet and around the exhaust.
B. Dry motor the engine at maximum motoring speed for 90 seconds to blow volcanic ash out of the engine.
C. Boroscope inspect the High Pressure Compressors (HPC) and High Pressure Turbines (HPT) at the 6:00 o’clock position to look for foreign material. If loose material is observed, dry motor the engine again for 90 seconds and re-inspect.
D. Change the engine oil filters.
E. Drain the oil system and refill with fresh oil.
The following actions are recommended for engines that have been exposed to volcanic ash and operated (on the ground or in-flight) in a volcanic ash environment (or if exposure is suspected or unknown) prior to the next engine start:
A. Inspect the engine inlet and exhaust areas for damage or erosion
B. Boroscope inspect the Booster, HPC, combustor, HPT, and LPT for evidence of erosion, foreign object damage, ash deposits, and cooling hole plugging.
C. Change engine oil filters.
D. Drain oil system and refill with fresh oil.
E. Schedule a repeat HPT boroscope inspection at the next aircraft A check or within 400-800 hours.
F. Perform a ground power assurance run.
G. Continue to use the engine and vigilantly review the engine trend monitoring data to look for possible negative engine performance.
Thus it is obvious why the aviation industry is being so cautious. Not only are there immediate complications concerning flight crew actions, the ATC response and the subsequent engineering actions, there is likely to be a longer term reduction of engine life, with a consequential requirement for more frequent overhauls.
The next problem with volcanic ash is that it is very difficult to detect, and, as has been explained, no one is sure as to exactly what concentration is safe. Research aircraft fitted with special sensors can be flown, but there are very few of them. LIDARs, a laser based radar, can detect the ash cloud, but again there are few of these equipments available and probably even fewer on any ships that could be sent to detect the clouds that have been coming our way. Satellite imagery can track the ash but only when the cloud is fairly dense. Aircraft radars are not designed to detect it as they operate in another wave band designed to pick up water droplets for thunderstorm avoidance.
Maps like this, for example, show the spread of ash over Europe as it was on the 17th April. They give a good indication of the general spread, but no indication of what is or is not safe:-

Based on this type of information the London VAAC issues advisories that look like this (the red lines show the spread of ash from the surface up to 20,000ft, and the green lines from 20,000 to 35,000ft):-

The jet streams on the North Atlantic are normally at around 30,000 to 35,000ft and travel from west to east at around 100kts plus – sometimes up to 150kts. They are highly variable both in speed and position, fluctuating from day to day as they snake around the world, the current one unfortunately has been tracking straight from Iceland towards the UK and Scandinavia. There has also been a large high pressure region out over the Atlantic, but this of course is a surface feature. The current jet stream at altitude has been fairly weak and was orientated from Iceland towards Scotland, staying that way for several days.
The problem has not only been confined to Europe. Transatlantic flights have been disrupted as well. There is an organised track structure between Europe and N. America that varies from day to day according to the position of the jet streams – the westbound tracks avoid the jet stream as much as possible because aircraft use more fuel and take longer when flying into the headwinds, the eastbound tracks are positioned as close as is possible to the jet stream to take advantage of the tailwind. There are several parallel tracks in each direction, set 60nms apart, with aircraft at 1000ft vertical intervals, and following 10mins behind each other.
As mentioned earlier, it is not easy to determine the exact position and density of the ash without sending research aircraft out to investigate, which in itself could be hazardous if far from land. Normally the track structure is much further north than shown below. This shows how the track structure has been modified for flights to the Iberian peninsula:-

And this next map shows where the normal track structure would be. I don’t know what the status of the more northerly ones is at the moment.

When Mt St Helens erupted in May 1980, the aviation world did not know so much about the ash problem then and was not so cautious. There was very little experience of the affects of ash (it was several years before the BA incident). Also the ash plume lay over populated areas where it was reasonably simple to keep track of its position. We all continued flying, but avoided the ash cloud. This is easy to do by day in visual conditions, but it is impossible to see it at night or when in cloud, so very circuitous routes had to be planned. During the Mt St Helens eruptions, we were still able to fly by night and in cloud because the position of the ash was well known, the density of traffic in that part of the US and Canada was relatively low, and there was a very good airways structure which could be used to avoid the ash. But it did mean going the long way round.
I have to say in Europe, I think the authorities have leant towards great caution (I hesitate to say they have been overcautious because I do not have the facts). For example on Thursday 15th April I would have thought it would have been possible to fly south out of London at a lowish level (say around 15,000ft) until well clear and then to climb to normal cruising altitudes. But no doubt this would have required a lot of re-planning by ATC, with a consequential reduction of capacity. However, I would have been very cautious about flying out over the Atlantic because of the difficulty of determining the exact position and nature of the ash cloud.
Over the weekend the ash in the UK descended to surface level and was found on cars. This photo was taken of the ash on his car by a pilot who lives about 15 miles east of Oxford. He said he had washed the car only a few days before and woke up to find this:-

And on Sunday, where I am currently living in the south of France, I could taste ash in the air.
In my trawl through the various websites I have picked out the following items. The first has some details of the BA ‘test flight’ on Sunday 18th April. The second is a report from Air Transport Intelligence of two Airbus test flights. The third is a report from the Finnish Air Force. The fourth is a press report about an air ambulance flight in Scotland. The fifth is a press report from an Icelandic professor of geophysics.
(1) British Airways flew a 747 yesterday (18th April) from London to Cardiff with only a test flight crew consisting of the two pilots, the Head of Flight Operations, the Head of Engineering, and the CEO on board. They started at 10,000ft and climbed in steps to 40,000ft, spending 5mins of level flight at each 5000ft step. The total flight time was 2hrs 46mins and after the flight the aircraft was examined at the Cardiff engineering base. The whole aircraft was inspected and the engines boroscoped before and after the flight, there were no immediate problems. Other airlines in Europe have done similar flights. However, the fact that someone can make a “test flight” and return the aircraft safely after exposure to some level of volcanic ash proves relatively little. Only a detailed examination of the hot section of the engine, probably right down to the microscopic level and including sectioning of first stage turbine blades and nozzle guide vanes to check the cooling passages for contamination, will prove that there is no long term damage.
(2) Airbus have used two previously-scheduled development test flights to fly into the ash cloud to monitor engine performance and to assess any potential damage caused by ash particles. “The post-flight inspection showed no irregularities. We have passed the information to the engine manufacturers and the airworthiness authorities and it will be the role of the authorities to make a decision based on that,” says an Airbus spokesman.
A380 MSN004, powered by Engine Alliance GP7200 engines, landed back in Toulouse at 18:00 local time yesterday after a 3hr 55min flight. A340-600 MSN360, powered by Rolls-Royce Trent 500s, landed at 19.40 after flying for five hours. The A380 operated within French airspace, while the A340-600 operated in French and German airspace. The Airbus spokesman says that during the test flight the two aircraft “would have visited altitudes that airlines would normally visit”.
(3) Next, here is a report from the Finnish Air Force. Some of their fighter aircraft when on a training flight training flight entered the area where there was only a very little ash. I understand the engines have been taken for thorough examination:-
16.04.2010 13:03
Ash particles a significant threat to aviation safety in Finnish Airspace.
The Air Force has investigated during Thursday and Friday the Lappland Wing F-18 Hornet fighters which were executing training flights during Thursday morning in Northern-Finnish airspace. At that time the airspace was still in general use.
After the planes landed they were inspected, and the engine intakes were found to be covered with “potato-flour” – like volcanic ash dust. One engine of one of the Hornets has been inspected with a boroscope. Based on the pictures it was established that even a short period flight in volcanic ash may cause significant damage to the engine.
The photos indicate that the ingested ash had melted in the heat of the combustion chamber at the temperature of around 1000 degrees C. The effect of melting ash blocking cooling channels in the engine will lead to overheating of engine parts and deterioration of material strength, and in the worst case, disintegration of components and destruction of the engine.
The Hornets subjected to volcanic ash will be checked substantially. At least some of the engines must be taken out and subjected to further investigation at Patria engine maintenance facility. Those engines which demonstrate signs of ash ingestion effects will be dismantled to determine the full effect of damages. At the same time the ash effects to the engine cooling passages will be determined.
The operative flights will be carried out routinely (i.e. identification flights etc.)
Despite the ash cloud the Finnish Air Force continues to keep one Hawk jet-trainer with air-sampling equipment in full preparedness. The plane will fly when the appropriate civilian authorities determine that the flight is necessary.
Based on the information gathered by the aircraft the amount of ash in the atmosphere can be inferred. The results are forwarded to the civilian officials, who determine the availability to the Finnish air space through different other sources.
The sampling plane will fly at varying altitudes and collect particle samples in the container. After landing the samples will be forwarded to the Defence Forces Technical Research Center at Lakiala. The results will be available in about two hours, after which they will be made available to Finavia. If necessary, the aircrew will report visual observations in real time. The atmospheric sampling aircraft is operated by the staff at Kauhala air base.
Pictures of the interior of the engines of the Finish F-18 Hornet:-


(4) And here is a press report from the coastguards in Scotland after an ambulance helicopter flight on Thursday 15th or Friday 16th (I am not sure which day it was):-
The helicopter was tasked to fly a seriously ill woman from the Out Skerries to the Gilbert Bain Hospital, in Lerwick. A coastguard spokesman said that after the hour long mission the helicopter was covered in a fine layer of dust which had been extremely difficult to wash off.
The crew only went out after ambulance services told them that the woman would probably not survive if they had to wait for the ferry which takes 90 minutes to reach the island. “What we did first was put it to the crew to see if they were prepared to fly or not. They were aware that another, quite large cloud of ash was on its way to Shetland.”
“You can’t physically see the cloud but the ash was starting to collect on the windscreen. They only really noticed that the helicopter was covered in ash when they got back to base.”
(5) Next, here is a report from Iceland:-
Published in Iceland Review Online16/04/2010 | 17:00
Geophysicist: Hard to Predict How Eruption Will Develop
Professor in Geophysics Páll Einarsson said it is hard to predict how the volcanic eruption in Eyjafjallajökull will develop. Geophysicists usually base their predictions on experience and little is known about previous eruptions in Eyjafjallajökull.
The only eruption on which they have some information occurred in 1821. “And it is limited what we can learn from one eruption. […] Volcanoes change during eruptions so the next eruption will occur in a changed volcano,” Einarsson told visir.is.
The 1821 eruption lasted for more than one year and resulted in significant ash fall. It stopped once in a while but then resumed. Einarsson said it is likely that the current eruption will carry on for some time—yesterday morning it grew in strength.
However, it has also happened that eruptions come to a sudden end. “But this is part of a longer course of events which began last summer. If the eruption stops suddenly in this location it is likely that it will resume in another location.”
Einarsson said the eruption in the Eyjafjallajökull volcano moved from the best possible location on the Fimmvörduháls mountain pass, the only place in the area that is ice free, to the worse possible place, where the icecap is thickest and where there is most risk for glacier bursts and ash fall.
So what do we need to do next? After all the recriminations have died down, and rather than everyone blaming each other it seems to me that there are two basic questions that must be answered. The first is for the UK Met Office which is charged with providing the forecasts for the London VAAC:-
1) Exactly what are the actual and forecast concentrations of ash at different locations and altitudes (g/m3) and other data such as particle size distribution and composition, and what can be done to improve the forecasts?
The second question is for the aviation industry and regulators:-
2) Exactly what is a safe concentration?
There is no doubt that there is a concentration which is damaging but equally there will be a level where the risk of damage is statistically insignificant (not zero). It is vital to find the answers to these two questions if we are to avoid repeating the problems of the last week.