No one was seriously hurt.
About 600 Southwest flights across the country were canceled over the weekend, and another 70 were grounded yesterday.
Southwest Airlines inspected 79 jets, representing 90 percent of its Boeing 737-300 models, and found cracks in three of them.
Poppy Bass, who returned from Key West yesterday, checked her itinerary online after seeing that the same flight to Philadelphia on Sunday, which left at the same time as hers, had been canceled.
"We just checked online and all the information was all there," Bass said as she waited in the baggage-claim area. "We were worried we were going to have problems, but nothing happened."
Federal aviation officials readied an order yesterday for emergency inspections on 80 U.S.-registered Boeing 737 jetliners like the one on which the fuselage tore open more than 30,000 feet above Arizona.
The inspections are aimed at finding weaknesses in the metal in the fuselage, but virtually all of the affected aircraft will have been inspected by the time the order takes effect.
The order is "certainly a step in the right direction," said National Transportation Safety Board member Robert Sumwalt, who is in Yuma with the board's accident-investigation team.
Friday's incident raised questions about the impact that frequent takeoffs and landings by short-haul carriers like Southwest put on their aluminum-skinned aircraft and the adequacy of the inspections.
Cracks can develop from the constant cycle of pressurizing the cabin for flight, then releasing the pressure upon landing.
Since there had been no previous accidents or major incidents involving metal fatigue in the middle part of the fuselage, Boeing maintenance procedures called for airlines to perform only a visual inspection.
But airlines, manufacturers and federal regulators have known since at least 1988 that planes can suffer microscopic fractures. That year, an 18-foot section of the upper cabin of an Aloha Airlines 737-200 peeled away in flight, sucking out a flight attendant.
Inspections of the fleet didn't pose much of a problem yesterday at Philadelphia International Airport.
"We did not have any stranded passengers in Philadelphia," Lupica said.
Daily News wire services contributed to this report