The eruption of Iceland's most active volcano has rekindled memories of last year's ash crisis which shut European airspace and sent disruption rippling worldwide.
Aviation officials say this week's development poses less danger and up to half the cancellations seen last year would no longer be necessary, as understanding of the risks improves.
But the pattern of previous disruption serves as a rough guide to potential pressure points from future ash clouds.
Here is last year's volcanic crisis in facts and figures.
* Most European airspace closed progressively, April 15-21
* 100,000 flights cancelled in total, peaking at 19,000/day
* Over 10 million people stranded or unable to board flights
* Airlines lost $1.7 billion in missed revenues
* Airports lost 250 million euros
* Markets worst affected: Finland, Ireland, UK (90 percent of flights cancelled)
* Biggest markets affected by value: UK, Germany, France
* Biggest revenue impact: UK/US transatlantic market
* Low-cost carriers were worse hit than long-distance carriers, cancelling some 61 percent of their flights
* Travel by business jets was the least affected
* 30 percent of total worldwide airline capacity was cut
* European capacity was cut by 75 percent, Africa by 30 percent, Middle East by 20 percent, others 15 percent
* Airline kerosene demand fell by 1.2 million barrels a day, compared with 4.3 million barrels consumed on a normal day.
* Emerging market currencies tied to tourism such as the Kenyan shilling and Turkisjh lira fell
* OECD said ash week cost the European economy $5 billion
* Travel and tourism, including transport, lodgings and related investment, comprise about 4 percent of West European GDP, according to the World Travel and Tourism Council.
* PricewaterhouseCoopers estimated each week of disruption destroyed around 0.025-0.05 percent of annual British GDP; the same would probably be true of other European countries.
* While hotels received fewer incoming tourists, some were able to raise prices to take advantage of stranded tourists.
* While one volcano wreaked havoc, the economy of the volcanic islands of the Azores, governed by Portugal, got an unexpected lift: traffic boomed due to flight diversions.
(Source: IATA, Eurocontrol, European Commission, Reuters)