New York - Delta Air Lines Inc, the world's largest carrier, and United Airlines parent UAL Corp on Tuesday posted first-quarter net losses totalling more than 1 billion dollars despite a drop in fuel prices, because of a deepening travel slump.

Delta reported net losses of 794 million dollars for the quarter. The airline said it would add a 50-dollar-fee for international travellers who check in a second bag - a move that will enable Delta to earn more than 100 million dollars a year.

Delta said it would ground 14 Boeing 747-200 freighters that it acquired when it bought Northwest Airlines in October because the jets were old and revenues from cargo had dwindled.

"We remain focused on making disciplined decisions about capacity, costs and capital, achieving merger synergies and finding new sources of revenue," Delta chief executive Richard Anderson said in a statement.

UAL reported net losses of 382 million dollars and said sales dropped 22 per cent to 3.69 billion dollars. United's passenger traffic tumbled 15 per cent; the decline in first and business class was 30 per cent.

"Our first-quarter results were particularly impacted by lower premium and business travel demand as the effects of the recession were felt worldwide and corporate clients cut their travel budgets," Bloomberg news quoted chief financial officer Kathryn Mikells as saying.

United plans to cut its capacity in its main jet operations by about 10 per cent in 2009 - this includes reducing domestic seats by 12.5 per cent and international seats by 6 per cent.