The International Air Transport Association estimates that aircraft grounded due to volcanic ash affected 1.2 million passengers per day for six days and resulted in total lost revenue of more than $1.7 billion. For the three-day period that covers April 17-19, when the disruptions were most widespread, losses totaled roughly $400 million per day for airlines. On April 18, the number of flights fell by as much as 79 percent from the same day the previous week (from 24,965 to 5,204), according to EUROCONTROL. A commercial aviation consulting analyst for Frost & Sullivan said the event "has affected up to 8 percent of global trade." He added that "it may take up to three years for the industry to recover fully" (a sentiment echoed by the IATA) and weaker carriers "may not make it without government help." In the shadow of that financial possibility, the safety actions have stirred controversy.
The UK's Civil Air Authority "led the way" in establishing the groundings, according to CAA CEO Andrew Haines. UK Transport Secretary Lord Adonis called the CAA's actions "overcautious." Haines is, so far, standing by the CAA's decisions. The Icelandic volcano Eyjafjallajokull's ash cloud "created an unprecedented situation for aviation and in particular the UK," according to Haines, who said they acted based on scientific evidence. "Without establishing what was safe and what wasn't, based on robust scientific data from the current ash cloud," the agency was not willing to reopen the skies regardless of pressure from the airlines, said Haines. The IATA, which represents about 230 airlines that comprise roughly 93% of scheduled international air traffic, believes earlier testing could have opened some airspace, sooner.
NASA's Unintended Volcanic Ash Encounter Flight (podcast)