Air traffic in Europe slumped by 11.7% in April because of flight cancellations caused by the volcanic ash cloud.
Figures released today (May 27) by the International Air Transport Association (IATA) showed the continent was the worst hit region by the Icelandic volcano.
Most other areas showed a growth in traffic.
IATA said traffic carried by North American carriers fell by 1.9% but airlines in Asia-Pacific (3.5%), the Middle East (13%), Africa (8.6%) and Latin America (1.2%) all reported a rise.
The Association said that globally traffic figures fell by 2.4% which had "interrupted" the industry's recovery from the recession.
The 11.7% fall in Europe compared to a 6.2% increase in March.
IATA said: "Uncertainty of service reliability in the aftermath of the ash cancellations and major unrest in Greece as a result of the currency crisis added to the weaker European demand during the month.
"Limited GDP growth expectations of 0.9% continue to dampen demand across the continent."
Giovanni Bisignani, IATA's director general and ceo, said: "The ash crisis knocked back the global recovery - impacting carriers in all regions.
"Last month, we were within 1% of pre-crisis traffic levels in 2008. In April, that was pushed back to 7%."
He said the fall in traffic could not have come at a worst time for Europe.
"Europe's slow recovery from the global financial crisis and its currency crisis are already a huge burden on the profitability of its airlines.
"The uncoordinated and excessive cancellations and unfairly onerous passenger care requirements rubbed salt into the European industry's wounds," Bisignani said.
He called on Europe to reform its air traffic management.
"We need leadership to deliver the Single European Sky, fair passenger rights legislation and continent-wide coordination," he said.
Tony Berry, HRG's industry and airfare distribution director, said the April drop in demand in Europe reversed two quarters of steady growth.
But he said: "With many airlines remodeling their service offering and stabilisation of the global economy we are optimistic for a continued increase in passenger demand.
"We are already seeing the first signs of easing market conditions, with clients in Asia Pacific beginning to relax travel policies.
"As the global economy continues to recover, there are early tentative signs that this trend is evident in Europe and North America, too."
www.iata.org