PHOENIX - After a face-to-face meeting with Mayor Nutter, US Airways chief executive Doug Parker says he is convinced that the city will be persuaded by "facts, not opinions" about the difficulties of the proposed massive expansion of Philadelphia International Airport.

And an executive of the airport's second-biggest carrier, Southwest Airlines, says he believes the expansion plan, which calls for construction of a fifth runway, "will die of its own weight" because of the costs involved.

Parker flew to Philadelphia earlier this month to meet with Nutter, amid public disagreement between the airport and its dominant airline about the need for a new runway along the Delaware River.

"The mayor called me and said, 'We should talk about this,' " Parker said in an interview. "We were obviously concerned . . . there is a difference of opinion about what things to do in what order" to alleviate airport delays and increase capacity at the city-owned airport.

In addition to the planned fifth runway, the city wants to lengthen two existing runways and add new terminal and parking facilities in an expansion that it predicts would cost $6.4 billion over 13 years. The airlines, which would bear most of the cost, say that the price would be much higher, about $10.5 billion, and that it could force them to reduce operations in Philadelphia.

After the Nutter-Parker meeting, both sides were more conciliatory, though they acknowledged that big differences remained.

Phoenix-based US Airways and other carriers argue that a new runway would not substantially reduce congestion in Philadelphia, because the big problem is the crowded airspace between New York and Washington.

Bob Montgomery, vice president of airport affairs for Southwest Airlines, said the city and the airlines should be working together as part of a national effort to redesign the airspace over the Northeastern United States, instead of wrangling over a new runway.

Montgomery predicted that the runway ultimately would not be built because of costs, which he said had not been well-established and would increase costs for airlines and passengers.

"The city doesn't have to pay for it, the airlines do," Montgomery said. "It's real easy for me to want a better house and a new car if you're going to pay for it."

Parker predicted that continuing discussions between US Airways and the city - he and Nutter have agreed to meet every three months - would settle the question of what was to blame for Philadelphia's airport congestion and how to fix it. Those facts, rather than competing opinions about the problem, will drive the solution, he said.

"I think our goals are the same: We both want Philadelphia to be one of the best airports on the East Coast," Parker said. "I give a lot of credit to the mayor. He said, 'I want to see it fixed.' "

Nutter's spokesman, Mark McDonald, said Thursday: "The administration is committed to infrastructure improvements as part of a plan to dramatically improve the environment for the traveling public."

A new runway apparently remains part of that. "The city has not changed its position with regard to what is needed at the airport," McDonald said.

The city is negotiating a contract with the engineering firm CH2MHill to lead the project management for the proposed expansion. The firm will refine cost estimates and will plan construction. In the planning process, the airlines hope to reach agreement with the city on causes of congestion and the solutions.

"When we agree, we'll know how to proceed," said Stephen L. Johnson, US Airways executive vice president for corporate and government affairs. "Once and for all, we'll get to the bottom of this. This is not some unsolvable thing."

US Airways' lease to use the airport expires in July 2013, and the airline has balked at signing a new lease until the expansion issue has been settled. City officials said earlier this year that if the airline did not sign a new lease by July 2012, they would seek an ordinance to set new rates unilaterally.

That threat is now off the table, and Nutter and Parker said in a joint statement Monday that both remained committed to getting a new 15-year lease signed.

The proposed new runway would displace the freight hauler UPS from 212 acres it owns along the Delaware and move the company to a smaller parcel on the airport's west side, next to a neighborhood in Tinicum Township.

That would require the demolition of 72 houses. The township and Delaware County are suing to halt the expansion.