UAL Corporation, the parent company of United Airlines, has reported a net loss of US$152 million for the first quarter ending March 31, the second consecutive period the airline has been in the red.

But UAL's pre-tax loss of $236 million was an improvement of $70 million year-over-year, excluding re-organisation items, a company statement said.

Despite a 0.6 per cent increase in consolidated capacity and a 1.4 per cent increase in consolidated revenue passenger miles from the first quarter of 2006, total operating expense, excluding special items, declined year-over-year by $149 million, or 3.2 per cent.

"We continue to generate significant cash flow by tightly controlling costs and improving ticket revenue growth in a seasonally weaker quarter, at the same time investing strategically in the customer and the enterprise," said Glenn Tilton, United's president, chairman and CEO.

"We are focused on our performance agenda, improving our product, our processes and, most importantly, our relationship with our customers," he said.

Operating earnings improved by $22 million from special items resulting from the reduction in the estimated liability with respect to litigation related to United's leaseholds at San Francisco and Los Angeles International Airports.