The International Air Transport Association (Iata) says airlines may lose $9bn
( 5.7bn) this year - nearly double the estimate made in March.
Director General Giovanni Bisignani, speaking at Iata's annual meeting, said it
was "the most difficult situation the industry has faced".
The crisis in the aviation sector has been caused by a steep fall in passenger
numbers.
There has also been a big decline in demand for air freight.
Iata predicted in March that losses for the global airline industry would reach
$4.7bn in 2009.
It has also revised its estimate of the losses for 2008 to $10.4bn, up from
$8.5bn.
It said that rising oil prices were also a threat to airline profitability.
It predicted passenger numbers would fall 8% compared with last year and that
cargo demand would fall 17%.
'I don't have cash'
Iata suggested that governments could help by lifting restrictions on some
routes allowing more cooperation between airlines.
"Liberalising key routes today would create 24 million jobs and $490bn in
economic activity," Mr Bisignani said.
The organisation said that 4,000 new aircraft are scheduled for delivery in the
next three years, but there are concerns that airlines may have to defer
delivery or even cancel their orders.
The chairman of Air India said he was considering delaying orders from Boeing.
"I don't have cash - what do you expect me to do," Arvind Jadhav asked
reporters.
But the chief executive of Qatar Airways, which has $27bn of planes on order,
said he wanted delivery to be speeded up.