The International Air Transport Association said Tuesday passenger demand in March plunged 11.1 percent from a year earlier, as the slowing global economy continued to quell consumers' appetite for air travel.
The trade group also acknowledged air travel demand will likely slow further as people fear the spreading swine flu.
Excluding the impact of a later Easter holiday, demand fell by about 9 percent.
North American carriers saw a 13.4 percent decline in international passenger demand. Carriers in the Asia Pacific region reported a 14.5 percent drop in passenger demand, while European carriers saw their international demand fall by 11.6 percent.
The trade group said airlines cut international passenger capacity by 4.4 percent, resulting in an average occupancy rate of 72.1 percent.
Rising concerns over swine flu could have a significant impact on traffic, the IATA said.
"It is still too early to judge what the impact of swine flu will have on the bottom line," said IATA Director General and Chief Executive Giovanni Bisignani. "But it is sure that anything that shakes the confidence of passengers has a negative impact on the business. And the timing could not be worse given all of the other economic problems airlines are facing."