International air travel suffered its largest ever post-war decline in 2009, IATA has reported.

New figures released today show that passenger numbers on scheduled air traffic dropped by 3.5% with an average load factor of 75.6%, while freight fell by 10.1% with an average load factor of 49.1%.

This year will not provide much respite either. Airlines are being warned they can expect to lose as much as $5.6 billion over the year.

IATA director general and chief executive Giovanni Bisignani said: “In terms of demand, 2009 goes into the history books as the worst year the industry has ever seen.

“We have permanently lost two and a half years of growth in passenger markets, and three and a half years of growth in the freight business,”

The bad news was only marginally alleviated by IATA’s figures for December 2009, which revealed a year-on-year decline of just 0.7% in international passenger capacity, while freight capacity actually grew by 0.6%.

Yields have also started to improve, thanks to tighter supply-and-demand conditions in recent months, although they remain about 5%-10% down on the previous year.

Passenger numbers in December also represented an improvement on November figures, with a 1.6% increase in traffic.

Bisignani said: “Revenue improvements will be at a much slower pace than the demand growth that we are starting to see. Profitability will be even slower to recover and airlines will lose an expected $5.6 billion in 2010.”

Carriers in Asia-Pacific, Europe and North America were badly hit by the decline, recording year-on-year declines in passenger numbers of 5.6%, 5% and 5.6% respectively, while African carriers were worst hit with a drop of 6.8%.

Middle Eastern carriers fared the best with an 11.2% growth in 2009 crowned by a peak in December of a 19.1% increase in passenger numbers. Latin American carriers saw a 7.1% increase in December. However, full-year traffic growth was constrained to 0.3% due to concerns about swine flu.