The head of the airline industry body IATA said on Friday that the tough conditions suffered by carriers hit by the global economic crisis were improving.

"The worst is over but the recovery will be a long story," Giovanni Bisignani, head of the International Air Transport Association (IATA), told reporters in New Delhi.

He said the aviation industry had forecast a worldwide drop in revenues of 80 billion dollars, from 535 billion dollars in 2008 to 455 billions dollars in 2009.

"A drop of this dimension will not be easy to address. It will take three or four years to return to the old levels," he said.

Bisignani said a similar crisis faced by the sector after the September 11 attacks had been tempered by relatively positive market conditions.

"Now we have an economy that is having a difficult moment," he said.