Directors of US Airways Group Inc. and AMR Corp's American Airlines late Wednesday approved a merger valued at $11 billion to create the world's largest airline by passenger traffic.

Philadelphia and eight other cities will be hubs for the combined carrier, to be called American and based in Fort Worth, Texas.

The two airlines were planning to announce the merger formally early Thursday.

The deal, which comes as American exits bankruptcy restructuring, also must be approved by the bankruptcy court and antitrust regulators in the U.S. Justice Department. Antitrust approval could take four to six months. Integrating the airlines' technology, reservation systems and labor contracts is expected to take at least 12 to 18 months.

Until then, each airline will operate its own flights and sell its own tickets. But the US Airways brand that transports nearly 70 percent of Philadelphia travelers will eventually disappear.

US Airways chief executive officer Doug Parker will lead the new company, and American CEO Tom Horton will be nonexecutive chairman until the first shareholder meeting next year.

AMR creditors will own 72 percent, and US Airways shareholders 28 percent in an all-stock transaction.

The new company will have a combined 98,000 employees, 1,500 planes, 6,500 daily flights, nine major hubs and revenue of nearly $39 billion.

It will be the market leader in two-thirds of the country - the East Coast and the Midwest - and the dominant U.S. airline in Latin America, but will still be weak in Asia, where United and Delta are stronger.

The merged company's passenger traffic - US Airways is fifth-largest U.S. carrier and American third - will lift it past United Continental and Delta as the world's largest.

The combination also would give American a stronger footprint on the East Coast where US Airways has hubs in Charlotte and Philadelphia, and allow US Airways to expand its reach across the Atlantic and into Latin America.

US Airways began with the name All American Aviation and grew from the mergers of Piedmont, Allegheny, PSA, America West and US Air passenger carriers.

Parker and his team spent the last year convincing American's union leaders, bondholders, creditors and anyone who would listen that the merger made sense to create a carrier that could compete with United and Delta. American had lost market share over the last five years, and Parker argued American's revenue shortfall would not be fixed by remaining independent.

Industry observers say the combination is the last big merger, after Delta and Northwest combined in 2008, United and Continental in 2010, and Southwest merged with AirTran in 2011.

The combining of these two carriers will "ultimately provide new air service opportunities to markets not currently served directly from PHL, especially international markets in Asia, South America and other important destinations," said Philadelphia airport CEO Mark Gale. "This merger should also strengthen the airport's position as an economic engine, serving as one of the new airline's major hubs, continuing to create jobs and help in growing our region's economy."

Whether airline mergers are good for consumers is a matter of debate. They can lead to service cuts in smaller cities and higher fares in some markets and routes. But mergers have also created a healthier and more profitable industry. Analysts expect regulators to approve the deal because there's very little overlap in the two carriers' networks. Only 12 city pairs are identical.

Parker has said Philadelphia will remain key to the new, bigger airline because of strong local origin-and-destination traffic and the region's large population.

He said all hubs will remain: Philadelphia, Charlotte, Phoenix and Washington, D.C., for US Airways. American's hubs are Dallas-Fort Worth, Miami, Chicago, New York, and Los Angeles.

Industry observers say Phoenix and Los Angeles are vulnerable to be downsized.

"The prospective merger will provide the traveling public with a larger more integrated air carrier capable of delivering expanded service to more markets," said Steven Carvell, dean of academic affairs at Cornell University's School of Hotel Administration.

US Airways will leave the Star Alliance with 27 partner airlines to join American's oneworld global alliance, with 11 partners, including British Airways.

"People in Philadelphia will be able to redeem their flights on British Airways, which has really good award ability through London," said Brian Kelly, founder of a blog and website, which offers tips for passengers to maximize airline frequent flier miles and credit-card points.

In previous airline mergers, frequent flier members of each carrier's programs were able to link their accounts, Kelly said.

"The biggest thing I like about American miles is they allow you to redeem for one-way awards at half the price of a round trip," he said. "US Airways, even if you only need to go one way, charges you the full round-trip in miles no matter what."

American's awards redemption begins at 12,500 miles, compared to 25,000 at US Airways, he said.

"I think that's something they will keep. I think the new frequent flier program will be based more on American's than US Airways' program. With the United and Delta mergers, they took the best aspects of both frequent flier programs."

The deal is a coup for Parker, who began pursuing a merger with the bigger rival soon after American filed for bankruptcy in November 2011. His argument was that American could succeed against bigger airlines only if it combined with US Airways.

American had losses of $12 billion in the last decade. US Airways has been profitable the last three years.

The two airlines discussed a deal for months, but were still hashing out the value of the merged carrier and who would run it. Horton wanted American to emerge from bankruptcy an independent company before considering any mergers.

The carriers were working to finalize a deal before Feb. 15, when confidentiality agreements with AMR bondholders were to expire.

Parker and his top lieutenant Scott Kirby, who ran America West and bought US Airways in bankruptcy in 2005, gained ground last April by winning the support of American's three major labor unions.

Recently, pilots and flight attendants from both airlines agreed on terms of how they would work together in a merger. The success of the labor discussions helped persuade American's creditors to follow Parker's lead.