The airline used lower fares and lower costs to outperform many of its larger rivals which are running at enormous losses.

Analysts expect US airlines to report operating losses of up to $3.5bn (�2.23bn) during the first three months of the year, in what will be one of the most difficult ever periods in the history of the aviation industry.

The combination of the war in Iraq and the deadly Sars virus has deterred many passengers from flying.

"Although our financial performance has been exceptional relative to the airline industry as a whole, Southwest, too, has been severely impacted by the lingering effects of the 2001 terrorist attacks and the war in Iraq," Southwest's chief executive James Parker said in a statement.

Southwest is the only major US airline to have stayed out of the red since the September 11 attacks.

New planes

The low-cost carrier boosted its profits by 14% between January and March, making $24m.

Despite the slump in air travel, Southwest continues to grow its revenues by winning passengers from its beleaguered competitors.

Revenues climbed by 7.5% during the period, while traffic rose by almost 5%.