Luckily for him, John Eichelberger has a finely developed sense of humour and an appreciation of irony. Both came in handy this week when the co-ordinator of the US Geological Survey's Volcano Hazards Programme found himself marooned in Paris, one of tens of thousands of people whose travel plans were disrupted by an Icelandic volcano whose name most are still struggling to pronounce.
Eichelberger, a member of an international committee of experts invited by the Institut de Physique du Globe de Paris to review France's volcano monitoring programme, touched down in the French capital a week ago on Tuesday. His trip, due to last five days, was now into its second week. "It was kind of amusing," Mr Eichelberger said on Wednesday. "I came here on volcano business. I was planning to go home on Sunday. I was supposed to address members of Congress today on the US volcano-monitoring programme. Instead, I'm at Unesco, talking about ash hazard to aircraft."
On the plus side, there are worse places in which to be stuck and Eichelberger found time for a spot of sightseeing. On Saturday he took a trip up the Eiffel Tower, but even this turned into a work outing. His photograph of the hazy, ash-dimmed skies over Paris - "the yellow tinge to the sunlight seemed volcanic to me" - was posted the same day on the website of the US Volcano Hazards Programme. And he has been in good company. Trapped with him has been Freysteinn Sigmundsson, Iceland's leading expert on the Eyjafjallajökull, the volcano that has brought European aviation to its knees. "He taught me how to pronounce it," said Mr Eichelberger, "but I've forgotten." Thankfully, the party came up with an easier name. "My wife, who is Russian, says the Russians have a new name for it: Mount Youwontbeabletogohome."
"Ash hazard to aircraft" is an esoteric subject that has made a few headlines in the past, but never before has it been responsible for such widespread disruption to so much airspace. Although commercial jet aircraft have been flying since the British De Havilland Comet took to the skies in 1949, the true nature of the threat did not register until May 1980, when several aircraft were damaged flying through the ash clouds thrown up by the eruption of Mount St Helens in Washington state in the US.
A paper published in the May 1993 edition of Flight Safety Digest, the journal of the Flight Safety Foundation, revealed that between 1983 and 1993 there had been about 10 volcanic eruptions each year sufficiently explosive to have sent clouds of corrosive gas and ash into the upper troposphere and lower stratosphere - the cruising altitude for modern aircraft. In the past 12 years, wrote Thomas J Casadevall, then project leader of the US Geological Survey's Volcanic Hazards and Aviation Safety team, no fewer than 60 aircraft - mostly Jumbo jets - had been damaged by encounters with ash clouds. Worse, seven had lost power, endangering the lives of 2,000 passengers.
More recent studies show that since the late 1970s more than a dozen commercial aircraft have lost engine power in ash clouds. Then, as now, according to a standing US Federal Aviation Authority briefing to pilots on potential flight hazards: "Volcanic ash clouds are not displayed on airborne or ATC [Air Traffic Control] radar … Most important is to avoid any encounter with volcanic ash." After Mount St Helens, Mr Casadevall said, "interest in the aviation safety issue grew rapidly in the early 1980s after several jumbo jets encountered ash clouds that had travelled several hundred miles from their sources" - sources that included the eruptions of Galunggung Volcano in Indonesia in 1982, Redoubt Volcano in Alaska in 1989 and 1990 and Mount Pinatubo in the Philippines in 1991. In a postscript more awestruck than scientific in tone Mr Casadevall concluded: "Nature remains the ultimate force."
One of the biggest wake-up calls came on December 15, 1989, when a KLM 747 en route to Tokyo from Amsterdam began its approach to Anchorage, Alaska, and descended through a cloud of volcanic ash thrown up by Mount Redoubt. The Boeing lost all four engines and descended 14,000 feet before they could be restarted; the bill for four new ones was about US$80 million (DH294m). "With less than a minute to impact, the pilot was able to start two engines and made it to the airport," Mr Eichelberger said. "That was a huge lesson."
But this week in Europe, it was a lesson that, ultimately, proved too expensive to remember. Since the 1980s, monitoring systems have been installed worldwide on many of the world's active volcanoes, aircraft manufacturers have developed procedures for pilots and the International Civil Aviation Organisation, an arm of the UN, has helped to establish a system of weather stations dedicated to the ash problem.
But, says Eichelberger, "The weak link in all this is we don't really know how much ash modern jet engines will tolerate, so the policy has been zero tolerance. Also, we don't have a well-established procedure for measuring the ash concentration in clouds." For now, then, avoiding the clouds is the only safe solution. The extensive monitoring system now in place means plenty of warning andlong-haul aircraft are often routed around or even over ash clouds.
This last week, however, although the ash cloud was relatively low and flights were able to pass high overhead, all aircraft taking off or landing in Europe would have had to pass through it - and with current knowledge that was deemed too risky. According to Sigurlaug Hjaltadóttir at the Icelandic Meteorological Office, which monitors Eyjafjallajökull, the mountain had given about a year's warning of its intentions. What no one could have predicted was the unusual convergence of factors that caused a week of air-traffic chaos.
"The activity under Eyjafjallajökull volcano has been monitored closely ... and we can't say we were surprised by the actual eruption," said Sigrun Hreinsdottir, of the Nordic Volcanological Centre at the University of Iceland. "As an eruption goes, it is actually not that big. However, the disruption it caused was a combined effect of many things; first it erupted under a glacier, second the ash is very, very fine, thirdly the wind direction caused the ash to move over Europe."
It began at a little after 1300 GMT on Wednesday, April 14. Iceland Review Online reported that because of the latest eruption, instrument flights below 30,000ft had been banned to the north and east of the area and all domestic flights to Egilsstaðir and Hornafjördur cancelled. The crisis wasn't to remain domestic for very long. The first hint of the problems ahead surfaced on PPRuNe, the Professional Pilots Rumour Network, at 2015 the same day. A mail flight from Bodø in northern Norway had reported ash clouds and the airport had been closed. It was to be the first of many.
"According to current wind and wind predictions, Norway airspace may close totally tomorrow as well as part of the Russian airspace," wrote one pilot, based in Iceland. "Lots of unhappy flyers tomorrow then." At 2125, National Air Traffic Services (Nats), Britain's air-navigation organisation, activated its Air Traffic Co-ordination and Communication Cell, an emergency alert system. The message read: "Due to extensive ash cloud from Icelandic volcanic eruption it is predicted that UK airspace will be affected from April 15. NOTAMS [Notices to Airmen] are being issued."
At 0950 the next day, Thursday, April 15, airlines had been notified by Nats that "from midday today until at least 6pm, there will be no flights permitted in UK-controlled airspace other than emergency situations". Throughout the following days, as most European airspace followed suit, trapping passengers in faraway places and, according to the International Air Transport Association, costing airlines an estimated $1.7 billion, Nats followed international protocol and stuck to its guns.
On Friday, April 16, Britain's Civil Aviation Authority stepped in to justify the closure in plain terms. The ash cloud, it said, was "an unprecedented event in Europe. While appreciating the severe inconvenience that the suspension of flights has caused, safety must remain our first priority. The procedures adopted in the UK comply with international aviation recommendations laid down by the International Civil Aviation Organisation."
Nats continued to issue regular bulletins, estimates of when skies might reopen, but hopes raised one day were dashed the next. By 1500 on Sunday, under growing pressure from the media and the air industry lobby, a note of defensive desperation had crept in to the announcements. Nats was "maintaining close dialogue with the Met Office and with Britain's safety regulator, the CAA, in respect of the international civil aviation policy we follow in applying restrictions to use of airspace. We are currently awaiting CAA guidance.
"We are working closely with government, airports and airlines, and airframe and aero engine manufacturers to get a better understanding of the effects of the ash cloud and to seek solutions." On Sunday evening, British Airways sent up a 747 from Heathrow on a three-hour test flight. On board was Willie Walsh, the airline's combative chief executive. "The conditions were perfect and the aircraft encountered no difficulties," BA reported.
On Monday afternoon, BA said inspection of the engines had revealed no deterioration while the engine oil and fuel filters had been sent for checks by Rolls-Royce. Analysis of flight data recorders "indicated that all four engines performed without fault for the duration of the flight". Across Europe, others, including Air France, KLM and even Airbus, carried out similar flights. And then, on Tuesday, the CAA unveiled its "new guidance" and, almost as suddenly as it had begun, it was over.
While acknowledging that: "Current international procedures recommend avoiding volcano ash at all times," the CAA had "drawn together many of the world's top aviation engineers and experts to find a way to tackle this immense challenge, unknown in the UK and Europe in living memory". So what had they done? "Manufacturers have now agreed increased tolerance levels in low ash density areas". They had, in other words, simply reduced the safety threshold.
BA's Mr Walsh told TV cameras early on Wednesday: "I took the view at the beginning of this that a blanket closure of airspace was not necessary," though he conceded that throughout the week there had been "occasions when the decision to close airspace could have been justified". Ash could be a threat to aircraft, he said, but he claimed that the levels of volcanic ash encountered by aircraft that had lost power in the past "were by a massive scale, significantly greater than the levels of volcanic dust, tiny particles, that we have experienced in the skies over the UK." Gordon Brown, out on the campaign trail with a little over two weeks to go before a general election, defended the closure, saying the government would "never be forgiven" if it hadn't put passengers' safety first.
As Mr Walsh became a media hero for having "recaptured" the skies, on Tuesday evening, Lord Adonis, the Britain's transport secretary, insisted that: "At every stage, decisions were based on the decisions of safety regulators … They have not been based on pressure from the airlines, and that is what the public would expect." Nats said it was "delighted … This brings to an end a period of disruption and uncertainty for air passengers. Our operation is fully staffed and already responding to the backlog of flights entering UK airspace."
Not everyone was quite so thrilled. At 1328 on Wednesday the British Met Office, responsible for monitoring eruptions as part of the global network of nine Volcanic Ash Advisory Centres, issued a terse response. It "acknowledges the decision by the CAA and the aviation industry to change the engine tolerance levels for the safe levels of ash ingestion into aircraft engines". Nevertheless, it added: "Eruptions from Eyjafjallajökull have continued through today with debris being emitted to around 13,000ft. Weather patterns continue to blow new areas of ash towards north-western parts of the UK."
At about 2200 on Tuesday, a BA flight from Vancouver had been one of the first to arrive at Heathrow. Getting hold of the boarding pass, said one jubilant Canadian passenger, had been like "winning a golden ticket for Willy Wonka's chocolate factory". It was, of course, sweet news for the airlines and marooned passengers everywhere, including Mr Eichelberger in Paris. But his message to Unesco had been "safety first", and he had watched the mounting by airlines revolt through the week with some apprehension. "Normally they are extremely conservative about ash because their planes are valuable and losing passengers to death is not a good corporate policy, but now there are horrendous financial pressures, as we've seen," he said.
"We have two problems; knowing exactly how much ash is there and how much ash you can safely fly through. The reason why they haven't been solved, I think, is that it would be very expensive - $10 million a pop to find out how much ash will destroy an engine, and to measure the ash you have to send an airplane through it, and there's been a kind of a reluctance to do that. "I'm sure that reluctance will go away now. Well, I hope so." Back in the PPRuNe chatroom, which by Wednesday afternoon had attracted more than 2,000 postings, there was concern among those who would be piloting passenger aircraft through the ash.
"It wasn't just the UK," claimed one, from Glasgow. "Exactly the same thing obviously happened the previous day when Eurocontrol's ash map magically changed after pressure from the EU." The unease was summed up by a pilot from Manchester. "Let the great experiment begin," he wrote. "The simple fact is that a 20-year-old, worldwide safety regime was overthrown at a two-hour meeting packed with British politicians and airline executives … tens of thousands of passengers will be used as guinea pigs to prove as self-evident the safety of airline profitability and political power …"