Much has been done to ensure that if volcanic ash were to drift over Europe as it did in April 2010, aviation would not be immobilised again.
When atmospheric volcanic ash paralysed aviation to, from and within Europe for a week in April 2010, the cost to the world's economy was estimated at €1.1 trillion ($1.45 trillion). Yet Icelandic volcanologist Dr Haraldur Sigurdsson warns: "The Eyjafjallajökull eruption was minuscule on a historic scale, and more powerful events are just a matter of time."
Since then, new information-gathering and decision-making coordination systems have been put in place and several "ash event" pan-European exercises have been staged to test the region's ability to cope with another eruption. The only question that remains is whether they will be effective in a real event. An extensive review of the system's weaknesses - so embarrassingly and expensively visible in 2010 - has been the policy change aimed at improving performance in Europe's aviation resource management systems.
Ash from Iceland's Eyjafjallajökull led to the closure of European airspace for a week in 2010
The airlines alone incurred €1.7 billion in revenue losses and costs, says the European Commission's then-director of air transport Daniel Calleja-Crespo. It has since become clear that flying in most of Europe's airspace that week could have continued safely. The aviation system's paralysis was the result of a total lack of preparation for such an event, which in turn meant there was no system for decisions on how to react, especially on a pan-European basis.
The most basic change of all - affecting everything else at a global level - has been a change to the relevant International Civil Aviation Organisation advice on how to react to atmospheric volcanic ash. The ICAO guidance at the time of the Eyjafjallajökull event was "avoid, avoid, avoid" without clarifying whether the advice should apply even if the ash density was known to be low. The ICAO's advice has been replaced with a requirement for airlines to refer to frequently updated ash-intensity information from the national or regional aviation authority and the Volcanic Ash Advisory Centre (VAAC) responsible for the region where the ash cloud is located.
One of the most surprising facts the 2010 ash cloud revealed was how the European Union had no executive system to coordinate operational decisions and actions in the event of an emergency that affected aviation in multiple EU states. The individual national aviation authorities made local decisions without reference to each other or a central authority.
The European Aviation Safety Agency remained silent when the ash arrived, with a layer of irony added by the fact that national aviation authority decision-makers and high-ranking politicians were unable to fly to work out their differences, having to rely on teleconferencing instead. To ensure no repeat, the EU has set up a European Aviation Crisis Coordination Cell (EACCC) to co-ordinate tactical policy. Chaired by Eurocontrol, the EACCC acts as a "conference bridge" to aid decision-making. An existing Eurocontrol tool for aiding air traffic flow control and management, EVITA (European crisis visualisation interactive tool for ATFCM), integrates ash pattern data supplied by the London and Toulouse VAACs to provide a zoning chart for atmospheric ash concentration, accessible via the Eurocontrol network operations portal, which also contains details on all other factors that affect flow management.
Globally, a new ICAO body, the International Volcanic Ash Task Force, will coordinate gathering and sharing worldwide scientific knowledge on atmospheric volcanic ash to advance understanding on its behaviour and effects.
Experts say that only enough is known about the subject to make it clear how much more knowledge is required. More detailed understanding of the damage ash does to turbine engines and airframes is an essential part of this, because real data gathered so far only comes from examining equipment inadvertently exposed to actual ash events, meaning the amount of data is limited and knowledge of precise conditions insufficient. Engines are required to be tested for resistance to airborne sand and dust, which is reckoned to be a good proxy for ash but is still not the real thing.
A fact that emerged from Eyjafjallajökull was that although there is considerable expertise covering operations in the vicinity of volcanic activity, practical experience of using this knowledge is localised within an area that is frequently affected by ash and its airlines - for example, Alaska Airlines. And volcanologists make it clear that ash varies with every eruption, so specific local knowledge cannot be transferred directly to other regions, although generic lessons can. If, as sometimes happens in Iceland, eruptions take place beneath glacial ice, the mix of melted water and ash creates a very fine dust which travels further than the coarse particles, and is just as harmful at similar densities.
In other areas of Europe, such operational experience was limited or non-existent at aviation authority level, although intercontinental airlines such as Lufthansa and British Airways had their own standard operating procedures for reacting to ash in other parts of the world.
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Meanwhile, Europe has been reviewing its ash-monitoring resources. The UK has set up a Volcanic Ash Advisory Group to review measuring methodology. Many systems used for monitoring other meteorological phenomena such as cloud can also be used to locate ash. Satellite surveillance is the most useful single large-area system for tracking ash, and the EUMetSat is geostationary over the equator constantly surveying Europe. When there is no cloud, it can monitor ash density.
Other means include radar, lidar (also used for cloud), weather balloons, and laser cloudbase recorders. In 2010, EasyJet's head of engineering Ian Davies, frustrated by what he thought was unnecessary grounding, contacted Dr Fred Prata, of the Norwegian Institute of Air Research (NILU).
Prata had been working on systems to track volcanic ash by satellite for years, in turn becoming probably the world's foremost expert. He was also working to develop an aircraft-mounted infra-red ash sensor (AVOID) that could provide pilots with a display resembling a weather radar to reveal the worst concentrations of ash. At FL200 it can see ash about 100km (54nm) ahead, providing there is no cloud.
Last December, EasyJet and Prata's NILU offshoot Nicarnica Aviation, using a piston-engined ultralight aircraft operated by the University of Dusseldorf, carried out a two-week trial in the shadow of Mt Etna, Sicily, which is always active, although sometimes it is only emitting sulphur dioxide rather than ash. The Flight Design CT ultralight is fitted with an AVOID pod and other atmospheric sensors.
The AVOID pod is expensive, making it unlikely airlines will choose to fit it, but EasyJet says it will fit the pod to 20 of its Airbus A320-series fleet, and hopes other European carriers will fit about 80 more.
If they do, this exercise will achieve much more than just providing tactical avoidance capability. When the next ash event happens, the crews of these aeroplanes can send reports to air traffic controllers, pinpointing the exact location of the ash. This will enable comparisons with the predicted location of ash densities so the algorithms used in the computer modelling can be refined and the accuracy and completeness of the surveillance picture provided by satellite sensors and ground-based lidar stations can be checked.
The whole exercise, Prata explains, is about building confidence in the total system and continually adding to the knowledge base.
Padhraic Kelleher, head of airworthiness at the UK Civil Aviation Authority, says: "The way forward begins with recognition that each airline is responsible for assessing risk before operating, and the regulator's responsibility is to make sure that they are competent and capable of doing so."
Therefore, the future entails better ash tracking, identification and measurement; more research on precisely how much ash it takes to damage engines and airframes; better coordination among all air navigation service providers and authorities during the event; and, finally, a transfer of risk management from the regulator to the operator.
The authorities will provide the information and a set of guidelines for making decisions, then the go/no-go decisions will be made by the airlines. Will this work? Certainly better than in April 2010, because it could not possibly be worse.