Volcanoes don't often make it to the headlines. Considering that at any given moment perhaps 20 volcanic eruptions are taking place somewhere on the planet, this is understandable. But when Icelands Eyjafjallajökull volcano began erupting on Apr 14, apart from the fiendish challenge of getting its name right, it triggered a first-rate crisis in commercial aviation. The combination of the volcanic flare-up and an atypical weather system-high pressure and northerly winds-wafted a noxious ash cloud over the British Isles and northern Europe. And there it stayed. Air navigation service providers could see only one way to fulfil their duty "not to direct flights into a known flight hazard"-they shut down up to 80 per cent of Europe's airspace the next day. After six days of chaotic disruption which grounded more than 100,000 flights, affected 10 million passengers and caused $1.7 billion in airline losses, the flight bans were lifted. There were other limited shutdowns over the next few weeks. Apart from huge economic losses, the ash cloud over Europe caused deep inconvenience to travellers, some family tragedies, and a great deal of recrimination. It showed that surface transport options were woefully inadequate to retrieve the hundreds of thousands of passengers stranded around the globe. It also proved-if proof were necessary-just how indispensable aviation has become to travel and commerce.
For decades, airlines have successfully dealt with ash clouds by the simple expedient of avoiding them. The International Civil Aviation Organisation (ICAO) has a time-honoured "zero tolerance" policy towards volcanic ash. Nine global Volcanic Ash Advisory Centres (VAACs) at Anchorage, Montreal, Washington, Buenos Aires, London, Toulouse, Tokyo, Darwin and Wellington track the location of ash and report it so that aircraft can then steer clear of it. In some regions, ash advisories are practically as routine as weather reports. While the area immediately around an erupting volcano is generally declared a no-fly zone, flights outside that are left largely to the airlines' discretion. Weather radar is ineffective in detecting ash clouds, so pilots rely on accurate forecasts of volcanic eruptions along their navigational routes and avoid the volcanic plume normally by at least 100 nautical miles. Consequently, each year millions of air travellers safely transit through volcanically active regions such as Iceland and the North Pacific without even realising it. However, in Europe's case, the magnitude and position of the ash cloud made it impossible to route aircraft so as to avoid the contaminated area because there was simply no clear airspace to do so. Ash filled the sky over the entire continent-one with the densest air traffic in the world-and created a situation unprecedented in aviation history.
Volcanic ash can be extremely fine-each particle less than two mm in diameter. Because it is ejected by very hot air from a volcano it is often flung up into the jet stream-10 km high or more. It is then transported by the wind and dispersed at heights commonly allotted to jet aircraft for best cruise. Some particles quickly fall to earth but lightweight ones can remain in the atmosphere for two to three years before they disappear. But until now the aviation industry has never needed to research the risk of harm, particularly to aircraft engines, of flight through areas of widely dispersed volcanic ash.Â
Ironically, the prevailing technique ofÂ ash damage prevention-avoiding it at all costs-is at least partly responsible for how little is known about the effects of flying through volcanic ash. But there's no doubt that it can result in serious harm to aircraft, especially to turbine engines. Ash particles easily melt as they pass through the engine. In the turbine, the melted materials rapidly cool, then stick to the turbine vanes and disturb the flow of high-pressure combustion gases. Ash particles jam moving parts and block fuel nozzles. They also clog ventilation holes intended to let in cooling air. They can dramatically reduce available power or even completely paralyse an aircraft engine. Larger particles can also inflict physical damage on compressor blades or other vital parts, sometimes making engine replacement the only option.
Two factors compound the problem. First, the damage is not always easy to detect and such damage might be cumulative. Therefore, the fact that Lufthansa, Air France, British Airways and KLM carried out a few test flights through ash from Eyjafjallajökull and reported that their planes appeared undamaged is hardly cause for complacency. With the present level of knowledge, it is difficult to predict the extent to which jet engines can tolerate mild to moderate ash ingestion. The simple fact is that engineers just don't know enough about the long-term effects of ash on engines. At the very least, ash ingestion will need more-intense maintenance procedures. And sophisticated engines are more susceptible to volcanic ash damage-since they operate at higher temperatures the particles are more likely to melt and turn into a ceramic glaze and clog them. Even a relatively modest increase in fuel consumption over the life of an engine would be a high price to pay for a few seemingly safe transits through ash clouding. The second difficulty is that the composition of the ash, and hence its potential to do damage, differs. Development of global standards specifying safe ash levels is likely to prove complicated partly because each eruption produces different size particles with unique chemical characteristics. Safety cannot be assured by tests on the ground with the wrong ash either. When engineers recently took apart a pair of turboprop engines that had flown more than 30 hours through various concentrations of ash they reportedly found traces of sulphur contamination and detected signs of internal corrosion and damage.
Apart from its lethality to engines, volcanic ash can abrade vital aerodynamic surfaces and degrade aircraft avionics and electronics. It can pit the pilots' windscreens, damage the fuselage and even coat the plane so much that its aerodynamic stability is altered.
Understandably, therefore, aircraft manufacturers like Airbus state that ash can cause costly damage to aircraft and recommend that flying through an ash cloud should be avoided by all means. At least three historical near disasters reinforce this opinion.
On June 24, 1982, a British Airways B747 entered a cloud of volcanic ash created by the eruption of Mount Galunggung, about 180Â km south-east of Jakarta, Indonesia. Ash particles sucked in through the intakes melted in the combustion chambers and stuck to the inside of the jet engines. Within minutes all four failed. The crew, however, handled the grave emergency competently and were able to glide far enough to exit the ash cloud. As the engine cooled during descent the molten ash solidified and enough probably broke off to allow air to flow smoothly through the engine, permitting a successful restart. Even so, landing the aircraft was a hair-raising experience as the pilots were virtually blindfolded by a blanket of ash which had scoured and obscured their windscreen.
Just 19 days later, on July 13, 1983, a Singapore Airlines B747 was forced to shut down three of its engines while flying through the same area. These incidents alerted the international aviation industry to the severe risk of flying through volcanic clouds, leading to a policy of avoiding ash at all costs. Yet on December 15, 1989, a KLM B747-400 inadvertently flew into a volcanic plume over Alaska. All four engines quit. Once the flight exited the ash cloud, the crew were able to restart and make a safe landing. Based on these successfully employed techniques, pilots who suffer unexpected loss of power in ash clouding are advised to throttle back and lose altitude, allowing cold air to be drawn into the engines. This, hopefully, shatters any molten glass formed by the ash so that the engines can be restarted.
The golden rule of skirting a volcanic plume by 100 nm has made safe flying possible even in regions of active eruptions. But during night-time, when pilots cannot see the plume, or if the actual winds aloft cannot be predicted, operations have sometimes been hindered. And pilots consider it just too dangerous to take off or land in ash. However, thus far the airlines have not rigorously compiled data from their experiences-the number of times and duration of transit by particular aircraft and the effect (even slight) on the airframe or engines. In April, scientists and engineers initially agreed that a concentration of ash of 0.002 g per cubic metre of air was probably safe. Then on May 18, a further "time-limited zone" was promulgated that allowed aircraft to operate through ash-contaminated airspace even at concentrations of 0.004 g per cubic metre of air. Experts feel that the vital next step will be to gather information about the effect of dispersed fine ash particles on thousands of engines. This will help build up a picture of cumulative effects, if any. It will also help airspace regulators to decide rationally if additional concessions of "safe" contamination levels are warranted.
The progress of very fine ash clouds is currently estimated by atmospheric sampling and sophisticated computer modelling. Europe's airlines strongly criticised this computer-based modelling which was used to predict ash concentrations and vociferously appealed to be allowed to decide what was safe and what was not. But can air traffic management (ATM) be divested of responsibility to keep aircraft clear of hazardous operating areas? If anything were to go wrong the aviation regulator would probably be called to account. And the airline operating such a system might find itself uninsured and definitely the target of civil and criminal lawsuits. The pilot cannot see what is around him/her; only ATM sensors can. And there's no altitude at which aircraft are guaranteed to avoid ash. Trying to descend below an ash cloud, for instance, can drastically increase the fuel burn of a jet engine and put it in the path of birds and obstructions. Why not just fly around ash? The trouble is that an ash cloud might be of very large dimensions. Besides it cannot be easily seen even in good light and not at all at night.
Satellites can track volcanic plumes fairly accurately, but are misled by moisture. They can only pick up two-dimensional patterns of dense ash without showing either altitude or thickness. The present satellite instruments-like the Seviri (Spinning Enhanced Visible and Infrared Imager) on Europe's Meteosat 8 and 9 spacecraft-were not designed for volcanic ash so they aren't particularly useful for determining ash concentrations. On the other hand, the US Calipso spacecraft has an instrument called Lidar (Light Detection and Ranging) which is more practical. By firing pulses of light towards the Earth and picking up the backscatter radiation it can show the top and bottom of the ash cloud, and thus its thickness. The ash concentration can be calculated by correlating the thickness with the two-dimensional picture of the mass loading (the mass of material entering the area per unit time). Ash concentration is what safety regulators and airlines need to know. However, on the downside, Lidar cannot distinguish ash from other particles like dust and soot. It needs to work together with infrared or other sensors operating at the necessary wavelength to make a precise determination of the presence of volcanic ash.
Another problem with most satellites is that since they circle the Earth they do not have a permanent view of an area of interest. This is sought to be remedied by the European Space Agency (ESA) which in 2018 is scheduled to launch a pair of geostationary Meteosat Third Generation (MTG) satellites on behalf of the meteorological organisation EUMETSAT. The satellites will carry infrared sensors that can track ash clouds and their concentrations, and transmit readings back to earth every 15 min, day and night. This should dramatically improve the tracking of future volcanic ash. ESA also plans to launch two space-based Lidar satellites in 2014.
Another device under active investigation is an aircraft-mounted ash detector system called Avoid (Airborne Volcanic Object Identifier and Detector), being tested by EasyJet and Airbus. The technology, based on passive infrared radiation, is designed to work like weather-detection systems already employed for spotting thunderstorms. It is being developed at the Norwegian Institute for Air Research, one of Europe's leading environmental and air-pollution research laboratories. Since volcanic ash is not distributed uniformly, it is important to be able to "see" it so as to avoid it or choose a transit where it is least concentrated. Even at present airlines make quite large and costly diversions to evade ash clouds. Avoid could help pilots spot ash clouds up to 100 kilometres away at altitudes of between 1.5 and 15 km, thus enabling shorter diversions and more direct routes.
During the recent European ash crisis there were complaints that engine manufacturers were not providing enough support and that warranties and insurance for engines were still being removed from aircraft flying close to ash. Ultimately, aircraft and engine manufacturers will need to incorporate more robust measures for ingesting ash at the design stage itself. They will also have to take a call on how much ash is safe for engines to ingest.
A Single Safe Sky
It is a truism that the only way to be 100 per cent safe in aviation is to remain on the ground. Flight operations, especially where the lives of thousands of passengers are involved, are a matter of careful risk assessment and risk management. And commercial considerations might sometimes cloud judgement of safety issues. Was it a coincidence that during the recent ash shutdown the airline industry was in the forefront of demanding a complete lifting of restrictions? The world's largest aerospace manufacturers were more cautious, stating that without reliable onboard ash-detection systems pilots should focus on avoidance of visible ash. Pilots were not so sure they wanted the ball in their court and warned against "rash" decisions to allow flights through the volcanic ash cloud. Governments acted circumspectly primarily out of safety concerns but also because they were anxious about liability. The political and legal fallout of just one major ash-related accident could be enormous. Questions would inevitably be raised about the wisdom of permitting flight operations in a less-than-safe environment.
The International Air Transport Association (IATA) was perhaps right to criticise decision making (that too after considerable delay) based only on computer simulations and theoretical modelling of the ash cloud. However, in the absence of published scientific data regarding what levels of ash concentration are safe for aircraft to operate, what else could the decision makers do? Is it OK to permit flying through ash and hope for the best?
But Europe's response to the crisis could certainly have been better coordinated. Its nationally fragmented airspace is partly to blame. The silver lining to the latest volcanic ash cloud is that European ATM is at last on course for a makeover. European Union transport ministers met in May and agreed that they would give "the highest priority to the acceleration and anticipation of the full implementation of the Single European Sky" (SES). SES is an ambitious initiative, launched by the European Commission in 1999, to reform the ATM architecture and provide a uniform and high level of safety over Europe's skies, while at the same time accommodating growing air traffic demands. It puts forward a legislative approach to meet future capacity and safety needs at a European rather than at local level. It is expected to bring enormous day-to-day performance improvements in flight operations; the benefits in emergency situations are only a small part of them.
Right now Eyjafjallajökull slumbers peacefully, the mayhem it recently unleashed practically forgotten. When it last erupted in December 1821, it continued intermittently spewing out ash for over a year, off and on. But then there were no airlines or aircraft to worry about. Someday, volcanic activity could resume or spread east to Katla-a much larger volcano, which lies below the adjacent ice cap-though there is no sign of that at present. If eruptions do recur volcanic ash could spread across Europe each time there is a sustained north or west wind. Hopefully the continent will be better prepared next time around.