The change in policy marks an increased preparedness for ash emergencies, but the awareness of ash risk to planes is still under investigation. Some argue the strategy is creating more chaos than needed.
"At the moment, here in Europe, the ‘no fly' zones are too big and much too cautious," wrote atmospheric scientist Fred Prata of the Norwegian Institute for Air Research in an email to Discovery News. "Helicopters in northern Norway have been grounded because of a plume in the stratosphere that is composed entirely of SO2 [sulfur dioxide] gas."
Following last year's Eyjafjallajökull eruption, EasyJet airlines agreed to test on-board air sensors meant to warn pilots of approaching ash clouds. But the technology, which Prata created, is not yet in place.
In December 2010, the International Civil Aviation Organization (ICAO) identified the low (teal), medium (gray), and high (red) concentration rates used to map plume levels. As part of the end to the Eyjafjallajökull crisis last year, on April 21, 2010, flying through an atmosphere that contained less than 2,000 micrograms of ash per cubic meter of air was deemed safe.
Following Saturday's eruption of Grímsvötn, the UK Civil Aviation Authority announced Monday that "any UK airline wishing to operate in areas of medium or high density ash, will need to have a safety case accepted by the CAA. Many airlines already have such safety cases in place and agreed for medium density. None has so far submitted a safety case to operate in high density ash."
Ash clouds are not soft powdery particles of burnt cinder floating in the atmosphere, but rather hard, sharp, and abrasive rock and mineral particles. At some point between no risk and some risk, a plane incurs damage that may require repairs or potentially lead to an earlier retirement of the plane down the road. Though it is difficult to judge as no engine has been built yet with a certified maximum ash tolerance level. The European Aviation Safety Agency is expected to formally request manufactures begin providing such data in 2012.
Currently, all airlines still consider flying through more than 4,000 micrograms of pulverized particles of stone and glass per cubic meter enough of a liability to require diverting or canceling flights.
But as EASA acknowledged in its April 12, 2011, proposal to place the burden of proof on the jet engine manufactures, establishing a one-size-fits-all threshold for atmospheric ash is unlikely anytime soon:
The European Aviation Safety Agency has been working on the issue of determining a threshold for volcanic ash since it was mandated to do so by the Transport Council conclusions in May 2010. The work to establish a single ash threshold is proving to be extremely challenging. It has become increasingly clear that in reality, every volcanic ash crisis may be different and the nature of the ash will be different. So establishing a "one size fits all" threshold is not viable in the short term. EASA will keep working on this issue, but it will certainly not be resolved in the short term. To note, this kind of threshold does not exist anywhere else in the world – even in areas like America, or Southeast Asia where there is a longer experience dealing with these issues – so it is not possible to adapt something from elsewhere in the world.
But while the safety threshold is still under debate, the danger threshold has long been known. In 1989 the amount of ash over Alaska's Redoubt volcano was 2 grams (2 million micrograms) per cubic meter, Marianne Guffanti of the U.S. Geological Survey, told Discovery News. Considering that planes can travel about 15 km (8 nautical miles) per minute, that much atmospheric debris can quickly accumulate to dangerous levels inside an engine. Just 10 hours after the eruption, the Redoubt ash plume caused all four engines of a brand new 747 jetliner to flare out. After a five minute drop from 27,900 feet to 13,300 feet, the pilots managed to restart the engines and land in Anchorage. The cost of repairs came to $80 million, including the replacement of all four engines.