ORT WORTH, Texas - With silver bells emblazoned with "American Airlines" and its logo, hundreds of employees at the airline's headquarters here cheered the closing of its merger with US Airways on Monday morning.

The combination of the nation's No. 3 and No. 5 carriers forms the world's largest airline company, with nearly 6,500 daily flights to more than 330 destinations in more than 50 countries and more than 100,000 employees worldwide.

"Our goal here is to go and restore American Airlines to its position as the greatest airline in the world," said American's new chief executive, Doug Parker.

AMR Corp., the parent company of American, and US Airways Group officially closed their merger Monday morning. Shares of the new company began trading Monday on the Nasdaq exchange under the ticker symbol AAL.

Parker rang the opening bell for the Nasdaq market remotely from a hall at American's headquarters. He was flanked by outgoing CEO Tom Horton, who will remain on the board as chairman, and former AMR CEO Robert Crandall.

During the celebration, employees were encouraged to ring their bells and cheer as loudly as possible, with a Nasdaq executive telling them the louder the cheers, the higher the stock price would go up.

Parker, Horton and Crandall also held a town hall meeting with employees at headquarters, answering questions on a variety of topics including the company's brand, its presence in New York, and whether the carrier will add more international flights.

"The biggest challenge is going to be the operational integration," Parker said. "It's not going to be easy."

Executives said they expect it to take 18 to 24 months to fully integrate the two carriers under the American banner. Consumers should not see any impact from the merger through the busy holiday travel period, and flights are expected to continue under the US Airways name for at least a year.

Horton, who led AMR as CEO through its two-year bankruptcy and merger process and will stay on as chairman until the first shareholders meeting next year, thanked employees for their hard work.

"We are putting American back on top," Horton said, who received a standing ovation from employees.

Crandall, who was CEO from 1985 to 1998, said he wishes he were young enough to come back to work at the airline.

"All of you have a chance to be part of renaissance, to go back to the day where anything but No. 1 is not acceptable," Crandall said.

Being the greatest airline, Parker told workers, means being one where customers want to fly and where people want to work. Changes have already occurred at the headquarters, where parking spaces are no longer assigned to management and a security guard stationed at the executive suite has been removed.

"Today's about celebrating and working," Parker said. "Tomorrow is all about working."