ATLANTA (Reuters) - Delta Air Lines Inc, the world's biggest air carrier, posted a second-quarter profit compared with a year-earlier loss, but its shares fell as much as 11.3 percent yesterday as revenue missed expectations and its outlook for the current quarter disappointed.

The company's third-quarter view raised concerns about the strength of the recovery for airlines, which are widely expected to post better results this earnings season as travel demand improves from recession weakness.

Delta closed down 3 percent on the day, paring its losses late in the session.

"People are just very concerned about the economy, and if you don't hear that life is going to be fabulous, the market is taking the stocks down," said Helane Becker, an analyst with Dahlman Rose & Co.

She said Delta's expected operating margin of 10 to 12 percent for the current quarter suggested a profit that was roughly flat with the second-quarter level, a disappointment as some analysts had called for earnings of more than $1.00 a share for the period.

Analysts on average expected a profit of 94 cents for the third quarter, according to Thomson Reuters I/B/E/S.

"People definitely wanted to hear an acceleration on the revenue line, an acceleration on bookings," Becker said.

Delta said the overall revenue environment was solid and advance bookings remained strong. Still, it said comparisons would become more difficult in July as it starts to lap a recovery that started last year, and added it was cautious in its outlook.

"The revenue environment is improving," Delta Chief Executive Richard Anderson said on a conference call. "I would characterize it as good, but not yet great." He said Delta expects to be "solidly profitable" for the full year.

Net income at Delta was $467 million, or 55 cents a diluted share for the second quarter, compared with a net loss of $257 million, or 31 cents a share, a year earlier.

Excluding items such as $90 million in profit-sharing expenses and merger-related costs, profit was 76 cents a share, compared with 63 cents expected by analysts, according to Thomson Reuters I/B/E/S.

Delta turned in an operating margin of 11.4 percent for the second quarter, the best it has seen in a decade, as profit sharing and higher fuel costs were partly offset by savings from the 2008 acquisition of Northwest Airlines.

Passenger revenue per available seat mile, an important measure, rose 19 percent as Delta operated fuller planes. Delta said it expected double-digit gains in unit revenue for the current quarter.

"I would have liked to have seen more volume growth," said Morningstar analyst Basili Alukos. He said traffic in terms of revenue passenger miles flown rose 1.7 percent in the quarter, suggesting there was still room to gain more passengers.

"It just shows you kind of a tepid recovery from the volume side," Alukos said.