The giant plume of ash that recently erupted from an Icelandic volcano hurled the airline industry into chaos. Now parties are considering what lessons can be learned - because the next eruption is just a matter of time.
Iceland's Eyjafjallajokull has calmed, but its bigger sister Katla lies in wait
As the global travel industry slowly returns to normal, a closer look is being taken at the volcanic ash crisis and whether the threat to airplanes merited closing most of Europe's airspace, stranding or delaying a million passengers, and costing the airlines nearly 1.3 billion euros ($1.7 billion).
Many questions are being asked by politicians, the airlines and scientists about a phenomenon that could occur at any time and, according to past trends, could be even more severe.
Airlines have long been aware of the dangers posed by volcanoes. Jet engines can suck in volcanic ash, which melts in the intense heat. The turbine blades are then coated and can clog up and fail. It has the makings of a potential catastrophe.
Up to 1.2 million passengers per day were affected
So when the huge cloud of ash from Iceland's Eyjafjallajokull volcano drifted into British airspace, the UK's air industry regulator banned all commercial flights. More than a dozen other countries - including Germany and France - followed that example, closing their airspace either partially or fully.
"Volcanic ash and jet engines don't mix, so safety is our number one priority," said Bob Jones, the UK regulator's head of operations. "We won't be able to lift those restrictions until we're comfortable that it's safe to have aircraft fly with members of the travelling public again."
While the mayhem negatively affected millions, it has also thrown up a flurry of scientific research. The silver lining to the ash cloud could be a better understanding of the exact danger of volcanic ash.
The British Meteorological Office is the Volcanic Ash Advisory Centre for the northeastern Atlantic. While the region it monitors is relatively small, it covers some of the busiest airways in the world. Its forecast of where the ash cloud was headed was followed closely by aviation authorities across northern Europe.
Each day a total of more than 16,000 flights were grounded. The airlines began to grumble but the international regulations were clear: if there was any volcanic ash in the airspace - any ash at all - no planes should fly.
More than 100,000 flights were cancelled
"Where you have a small chance of that happening, it would be very wrong to say, let's give it a try. This is a matter of life and death."
But as the flight ban dragged on, it quickly became more a matter of life and death for the airlines, which were losing about 150 million euros a day. Some were in danger of going under financially and they began to complain that the authorities had overreacted.
British weather forecasters used a computer program to predict where the wind would carry the ash cloud and how quickly it would disperse. The program was first developed after the nuclear reactor accident at Chernobyl in 1986.
How do you balance economic fallout for airlines against passenger safety?
Britain's Met Office says it is tried and tested. But Giovanni Bisignani, head of the International Air Transport Association, is angry that a great swathe of northern European airspace was closed purely on the basis of computer modeling.
"I call it a European mess because we did not focus on figures and facts. Europe was using a theoretical, mathematical approach. That is not what we need," he said. "We need test flights to go into the atmosphere, assess the ashes and then take decisions."
In fact, it has emerged that the Met Office could not establish a complete picture of the cloud over Britain until almost a week into the crisis because its specialist monitoring jet was out of action. The BAe 146 was the only plane equipped with state-of-the-art measuring instruments that could map the full extent of the ash.
Yet by the fourth day of the shutdown, European airlines like Lufthansa, KLM and British Airways had flown a number of their own test flights. They all reported no damage to their jet engines. Peter Sammonds, a volcanologist at University College, London, said this underlines the fact that it is not enough to rely solely on weather simulations.
"That sort of initial monitoring of the volcano, the modeling by the Met Office, probably needs to be backed up with more intensive atmospheric sampling to try and map the distribution of the ash in the atmosphere somewhat more accurately to provide better input into what the next decision should be," he said.
Test flights by research aircraft revealed interesting data. The ash cloud contained basalt, not the more damaging substance andesite. The ash concentration was also extremely low - no more than 100 micrograms per cubic meter of air.
Jet engine manufacturers said the cloud would need to be about 20 times denser to damage turbine blades.
After six days, all European airspace was officially judged to be safe and all remaining flight restrictions were lifted. It is estimated that the airlines lost more than a billion euros due to the shutdown.
European air traffic authorities admit they have been on a steep learning curve and now have a more flexible approach to volcanic ash.
Just a preview
Just as well, according to Iceland's President Olafur Grimsson. More ash could be on the way - much more, in fact, when Iceland's giant Katla volcano erupts.
Airlines have been vocal in their criticism of the blanket airspace closure
Katla erupts roughly once every one hundred years and the last time it lost its top was in 1918.
Siim Kallas, the EU's transport commissioner, has said he will begin working this week with colleagues to lay out a road map for similar events. The list of questions he faces is daunting, ranging from determining the safety threshold for different engines, weighing potential danger against economic fallout and balancing passenger rights against the industry's health.
"We needed a fast, coordinated European response to a crisis," he told reporters. "Instead, we had a fragmented patchwork of 27 national airspaces. We need a single European regulator for a single European sky."
Kallas has said he will propose speeding up the plan to unify control over all European skyways.
Stephen Beard (jam)
Editor: Nathan Witkop
The research made headlines and national stars of its two lead scientists. Stem cells, they said, can be created from blood cells. No sooner had the papers been published than doubts began to emerge.
A Berlin court has ruled that anatomist Gunther von Hagens will be allowed to open a museum displaying preserved human bodies and body parts. The museum is set to open in January 2015.
Bankers and investors are questioning whether it's worthwhile to invest in fossil fuels, especially in light of new climate agreements that could leave the materials in the ground forever.
New findings show that beavers and Arctic ground squirrels are contributing more to climate change than previously thought. Information on wildlife's role in global warming will help inventory greenhouse gas sources.