If you're going to fly around volcanic ash, first you have to see it up ahead. New Scientist flies shotgun on Sicilian field trials of a new sensor system
I'M IN a helicopter, flying low over the verdant foothills of mount Etna in Sicily. To my left, a tiny light aircraft is approaching the immense volcano's sweeping flanks as an ash plume rises from it. The diminutive plane looks like a bug buzzing a tetchy grizzly but its size belies the major impact it could have: it is carrying a raft of experimental instruments that could reduce the mayhem that restless volcanoes cause to aviation.
Aircraft engines must be protected from silicate-based volcanic ash particles. That's because they melt at engine-operating temperatures, coating turbine blades with thick, glassy gunk that blocks airflow, hindering fuel combustion and causing engines to cut out. Currently, the International Civil Aviation Organisation tells pilots to avoid flying in ash if its concentration is above just 4 milligrams of ash per cubic metre. That's why in the spring of 2010, when ash began spewing from the Icelandic volcano Eyjafjallajökull, aviation in Europe was grounded for extended periods between 15 April and 17 May. It cost the aviation industry billions of dollars.
Sensors attached to planes are needed to let pilots detect ash clouds up ahead so they can still fly but just navigate around them - much like weather radar warns them of storms. But the geochemistry of volcanoes varies widely and no one knows which are the best particles and gases to detect in-flight to help guide aircraft around ash clouds.
So the scientists I'm observing at the landing strip at Calatabiano, Sicily, are using a light aircraft to do two things. First, they are performing initial low-altitude, low-speed tests on an ash sensor developed at the Norwegian Institute for Air Research (NILU) in Kjeller, funded by the UK airline Easyjet. Second, Konradin Weber at Dusseldorf University of Applied Sciences in Germany is training four different sensors on Etna's ash-and-gas plume, and exploring what other chemical markers might help predict trouble for pilots.
NILU's Fred Prata says his sensor comprises a pair of fast-sampling infrared cameras - one seeking telltale IR absorption at a wavelength of 10 micrometres and the other at 12 micrometres. Software combines these to detect silicate-containing ash particles of 2 to 40 micrometres in diameter, the size that wrecks engines. This, Prata tells me in the airstrip's tin hangar, measures the ash "dose" ahead of the plane, how far away it is and its altitude. Combining this with lower-resolution satellite data allows the crew to work out an alternate course. His tests last week were encouraging, with a very low false-positive rate, but needs testing at airliner speeds and altitudes.
Out by the runway, Weber says other volcanic emissions could provide important information too. His equipment includes a counter for micrometre-scale particles, a nanoparticle counter, an ultraviolet detector for measuring sulphur dioxide concentration - which can indicate heightened volcanic activity - plus a hydrogen sulphide/carbon dioxide meter. The sulphur dioxide sensor gave Icelandic airport authorities the confidence to reopen airports after the Grímsvötn volcano erupted in May, for example.
Konradin hopes that nanoparticles on the breeze might also give early warning of ash ahead. "It's a new approach," he says. "Nanoparticles might give us an indication of volcanic ash plumes, and may be a way to tell you the age of the plume and how it is developing."
For airlines like Easyjet, which lost £55 million in the 2010 groundings, sensors to help keep planes flying cannot come soon enough.
She's gonna blow
The imminent threat of eruption by the enormous ice-covered Icelandic volcano Katla has helped focus the minds of the airline industry - because it could pump 10 times more ash into Europe's skies than Eyjafjallajökull did in spring 2010.
Throughout history Katla has erupted every 40 to 80 years - but it has not done so since 1918 - making it 14 years overdue. And recent seismic rumblings suggest magma may once again be stirring up beneath Katla.
Ian Davies, engineering chief at UK-based airline Easyjet, says it is vital that technology be in place to keep planes airborne. "This large scale grounding of flights should not happen again," he says
