Airline Safety - Ashy Disruption

For decades, airlines have successfully dealt with ash clouds by the simple expedient of avoiding them

Volcanoes don’t often make headlines. This is understandable, considering that at any moment perhaps as many as 20 volcanic eruptions may be occurring somewhere on the planet. But when Iceland’s Eyjafjallajökull volcano began spewing ash on April 14 this year, 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 1,00,000 flights, affected 10 million passengers and caused $1.7 billion (`7,650 crore) in airline losses, the ban on flights was lifted. There were other limited shutdowns over the next few weeks. Apart from the huge financial loss, the ash cloud over Europe caused deep inconvenience to travellers, some minor 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—as if proof were necessary—just how indispensable aviation has become to travel and commerce.

Stay Clear

For decades, airlines have successfully dealt with ash clouds by the simple expedient of avoiding them. The International Civil Aviattion 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 and report the location of ash clouds to enable airliners to steer clear of them. In some regions, ash advisories are almost as routine as weather reports. While the area immediately around an erupting volcano is generally declared a no-fly zone, flights outside it 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, every 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 that has the most dense air traffic environment in the world. This created a situation unprecedented in aviation history.

Volcanic ash is extremely fine with each particle being less than two millimetres in diameter. As it is ejected by very hot air from a volcano, it is often flung up into the jet stream about 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 the earth but lighter ones can remain suspended in the atmosphere for two to three years before they finally disappear. But until now, the aviation industry never needed to research the possibility of damage to the aircraft and particularly to the engines during flight through areas of widely dispersed volcanic ash.

Dreadful Damage

Ironically, the prevailing technique of 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 is 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 highpressure combustion gases. Ash particles jam moving parts and block fuel nozzles. They also clog ventilation holes designed 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 do not know enough about the long-term effects of ash on engines. At the very least, ash ingestion will need more-intense maintenance procedures. Sophisticated engines are more susceptible to volcanic ash damage as they operate at higher temperatures and 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 heavy 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 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.