Airlines had canceled about 750 flights for Thursday as of late afternoon, according to flight-tracking service FlightAware.com. That was the lowest daily tally of halted flights since airlines began cutting their U.S. flying on Sunday ahead of the storm.

Delta Air Lines (DAL.N) expected to operate about half of its roughly 260 flights at LaGuardia on Thursday. At John F. Kennedy International, Delta operations are near the normal schedule, said spokesman Morgan Durrant.

United Continental (UAL.N) expected to have a "more-or-less normal schedule" of flights at Newark, New Jersey, where it is the dominant carrier, and JFK, according to spokesman Charles Hobart. "We're looking to concentrate any cancellations required by airport conditions to the United Express regional operations," he added.

Meanwhile, American Airlines planned to build up to full schedules at LaGuardia and Newark. Spokesman Kent Powell said the AMR Corp (AAMRQ.PK) unit added extra flights into JFK to assist customers that had been stranded by cancellations earlier in the week.

New York-based JetBlue Airways (JBLU.O) said it planned to operate 80 percent of its total flights on Thursday, ramping up to a full schedule by Saturday. US Airways (LCC.N) began flights at JFK and Newark on Thursday and will resume service at LaGuardia on Friday, spokeswoman Michelle Mohr said.

U.S. carriers, which have canceled nearly 20,000 flights from Sunday through Thursday, have lost millions in revenue in Sandy's wake, airline watchers said. The New York-area airport closures had a trickle-down effect as airlines were forced to cut flights in other major cities.

John Wensveen, head of airline advisory services at Radixx International, which provides distribution systems and management consulting, said the cost to airlines from Sandy was likely $700 million to $1 billion, including lost revenue from canceled flights and expenses involved in re-starting operations.

"This is one of the most significant things that's happened to the industry in a long time," he said.

Ray Neidl, an analyst with Maxim Group, said things should get back to normal by the weekend.

"Most airlines will take a (financial) hit in the fourth quarter; we don't know the magnitude yet," Neidl said this week.

If there is any silver lining for airlines, it could be that Sandy hit during a period that is typically slow for leisure and business travel.

"If this storm in its full magnitude had come through in July, it would have been far more disruptive," said George Hamlin, a transportation consultant in Fairfax, Virginia. (Reporting by Karen Jacobs in Atlanta; Editing by David Gregorio)

• A Permanent Economic Emergency