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ENVIRONMENT Last modified on March 7, 2012

Clear the air

Doug Johnson from the UK’s Met Office reflects on the lessons Europe has learnt from the volcanic ash cloud crisis that closed most of its airports last year.

The impact of the Eyjafjallajökull volcanic eruption in 2010, and to a certain extent the Grímsvötn eruption in 2011, caused an unparalleled crisis in European aviation. 

On April 14, 2010, volcanic eruptions from Eyjafjallajökull intensified sending a plume of ash high into the atmosphere, which was quickly blown over the North Sea and then dispersed over a very large area of central and northern Europe. 

Within three days commercial aviation movements through the airspace of 23 European countries had ceased and restrictions were in place in two others. Over 300 airports, representing 75% of the European network, closed. 

Eurocontrol estimated that more than 100,000 flights were cancelled affecting the travel plans of around 10 million passengers, many of whom would be stranded for several days having to seek other methods of travel to get to their destinations. 

The airlines estimated their losses to be in the region of €1.4 billion, the airports €250 million, groundhandlers €200 million and air navigation service providers €175 million with wider impacts on European economies beyond this.

In response, the EU and Eurocontrol established the European Aviation Crisis Co-ordination Cell (EACCC) and, through ICAO instigating the International Volcanic Ash Task Force (IVATF), there was a global rethink of the standards and recommended procedures (SARPs) that are used to guide the regulated regime used during volcanic ash events. 

It has long been known that volcanic ash can be a risk to jet engines, potentially causing all four engines on a B747 to flame out. This was famously shown to be the case in two incidents – on June 24, 1982, when BA Flight 9 flew through the ash from Mount Galunggung and on December  15, 1989, when KLM Flight 867 flew through the plume from Mount Redoubt. 

Fortunately, in both cases, the pilots were able to recover their engines after descending several thousand feet. 

As a result of this and other incidents, ICAO set up nine regulated, Volcanic Ash Advisory Centres (VAACs) around the world to give advice to the aviation community on the advection and dispersion of ash clouds when a volcano erupts. 

Since 2002, the International Airways Volcano Watch Operations Group (IAVWOPSG) has been in operation to give guidance on volcanic ash avoidance, monitoring and dispersion. It advises ICAO what SARPs need to be included in Annex 3 to the Chicago Convention, which stipulates what meteorological services (including advice about volcanic ash dispersion) should be provided for international air travel.

Once they have been informed of a volcanic eruption in their area of responsibility the main role of the VAAC is to: 

(a) Monitor observational data where possible (using satellite imagery, ground-based remote sensing, scientifically instrumented research aircraft) to detect the existence and extent of an ash cloud

(b) Forecast the movement and dispersion of the ash cloud using transport and dispersion models even when the cloud moves into another VAAC’s area of responsibility

(c) Issue advisory information on the extent and forecast movement of the ash cloud

VAACs are responsible for issuing volcanic ash advisories to state flight information centres and Meteorological Watch Offices (MWOs), which are normally run by the state’s national met service. The MWO then has the responsibility for producing volcanic ash significant meteorological information (SIGMETs) for that state’s Flight Information Regions (FIRs) and then it is up to the state’s aviation authorities to decide whether the aviation community is further informed through NOTAMs (Notice to Airmen) or ASHTAMs.

In November 2004, the European system established to follow this process was found wanting when the London VAAC provided advisories of an eruption of Grímsvötn that lasted a few days and spread a narrow plume of volcanic ash over parts of Scandinavia and Eastern Europe. 

Many of the SIGMETs and NOTAMs that should have been produced did not appear and, as a result, ICAO and Eurocontrol put together a task force to produce a European and North Atlantic Contingency Plan for Volcanic Ash. 

This was eventually implemented in 2006 and one of the components of the contingency plan was that the process should be tested by running exercises every six months – since then these have been carried out to ensure that all stakeholders are familiar with the process in the event of a real eruption.

So in April 2010, the London VAAC, ICAO and Eurocontrol were relatively content that Europe could handle anything that an Icelandic volcano could throw at them. What we were not prepared for was: 

• An eruption that would last for 39 days where the ash was emitted into a stable meteorological situation that allowed ash to stay in the atmosphere for an extended period (5 to 10 days) without being washed out over Europe and the North Atlantic - some of the highest capacity airspaces in the world. 

• The impact of the IAVWOPSG’s lack of success over the previous 

10 years in establishing from the engine and airframe manufacturers a quantitative ash mass concentration that was safe for commercial jet engines to fly through. The official guidance to this day from ICAO is that the VAACs should give advice about where ‘any volcanic ash’ is in the atmosphere and what pilots should do if they encounter ‘visible’ ash.

Thus, on several occasions during the eruption large areas of Europe and the North Atlantic were affected by ash, albeit in some places of relatively low concentration. 

The UK’s Civil Aviation Authority (CAA), which regulates the London VAAC on behalf of ICAO, wisely took the decision early on during the eruption that the only way to minimise the area that would be closed to flights by European regulators was to get a recommendation from the engine manufacturers about what was a safe level of ash mass concentration for commercial aircraft to fly through.

Over the period of 10 days several international teleconferences were convened with representatives from all the engine manufacturers and eventually two ash mass concentration thresholds were agreed upon. 

The CAA then asked the Met Office London VAAC to provide a range of supplementary products to the standard ICAO ash products that depicted where these thresholds were forecast to be up to 24 hours in advance. 

This was a major challenge to the London VAAC. Not only was the Met Office being asked to provide forecasts of ash mass concentrations, it was being asked to do so within a matter of days. 

It also led to a change in the European and North Atlantic Contingency Plan which introduced low, medium and high risk areas based on the new ash mass concentration thresholds. 

The changes also resulted in airlines being asked to produce safety risk assessment cases for flying in areas that potentially contain different intensities of ash. The aviation authorities, if they thought appropriate, could then identify danger areas rather than closing air space. This would allow the airlines to make informed decisions about where they should and should not fly.

The London VAAC was in a fortunate position that it had a tried and tested atmospheric dispersion model called NAME. 

NAME has been used and developed since 1986 and has enabled the Met Office to provide reliable advice to government and emergency services about chemical pollution and nuclear contamination, and to take a leading role in the VAAC community from its inception. 

It has been benchmarked on many occasions with other dispersion models and has been audited and peer reviewed by the scientific community over the years and always been found “fit for purpose” and world leading in many aspects. 

However, a major challenge is that all volcanoes are different and the size spectra of ash particles ejected and the ash mass ejection rate, are very difficult to estimate and change relatively rapidly. 

These parameters are fundamental to being able to provide accurate predictions of where ash will be in the atmosphere several hours or even days in advance. 

The Icelandic Meteorological Office did a fantastic job in providing the London VAAC with quantitative observations of the volcano source strength which enabled the London VAAC to ensure the accuracy of our predictions. We were able to verify the predictions using scientifically instrumented aircraft flying within the newly defined low risk ash areas. 

Every time these aircraft flew on scientific-based missions they were able to verify that ash of appropriate concentrations were found in the areas that the London VAAC were providing warnings for and that the predictions were accurate to within a factor of 2 to 5.

Not surprisingly though, it proved difficult to convince the aviation community that, used with the right observations, we had a tool that could give good advice to the aviation authorities and airlines about where ash of certain concentrations would be dispersed to in the atmosphere. 

It took some time for everyone to be aware that the ash areas being predicted by the London VAAC were not necessarily full of ash – in fact, the further away from the volcano the more likely it was that the ash would be present in thin layers and the VAAC was trying to predict what the peak ash mass concentrations were likely to be within these layers. 

A significant amount of resource and time has had to be committed by the London VAAC in informing and engaging with the aviation community on this subject and this is continuing today. 

The are a large number of lessons to be learnt by the global aviation and VAAC community from the European experience of the impact of volcanic ash in a crowded, high capacity airspace. 

We await, with some expectation, the results of the ICAO International Volcanic Ash Task Force on volcanic ash and whether a more globally harmonised approach to volcanic ash plans can be achieved. 

Recent experiences of how the ash from the Chilean volcano was observed and predicted to have advected around much of the southern hemisphere this autumn by the various VAAC’s dispersion models indicate that change is required to the existing global ICAO guidance. 

One thing that can be said with some certainty, is that whether the regulatory regime closes airspace or requires a safety risk assessment case for flying in different levels of ash, the VAACs will have to give predictive guidance of where certain levels of ash concentration are going to be up to 18 hours in advance and will have to give more hard evidence of the observational data indicating where ash is at the start of the prediction time period.

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