May 1 (Bloomberg) -- Continental Airlines Inc., Delta Air Lines Inc., United Airlines and US Airways Group Inc. cut flight capacity to Mexico as concerns about swine flu reduces travel.

The service reductions to Mexico, where the flu formally known as H1N1 originated, are the first by U.S. carriers and leave American Airlines as the only airline among the nation’s biggest with international operations that hasn’t trimmed Mexico flights.

“Anecdotal reports and checks of airline-booking Web sites all indicate precipitous traffic drops to Mexico, and it’s very expensive to fly near-empty airplanes back and forth, particularly on international routes,” said Douglas Runte, a Piper Jaffray & Co. analyst in New York. He doesn’t rate Continental shares.

AirTran Holdings Inc. joined the larger carriers by trimming two weekly flights to Mexico.

Continental’s new schedule, which begins May 4, puts smaller jets on some routes and trims flight frequencies so all 29 Mexico destinations keep service, the Houston-based company said today. Continental has the most flights to Mexico of any airline.

Continental became the first major U.S. carrier to temporarily pare operations in the country hardest hit by the new strain of flu.

Delta, the world’s biggest carrier, is “making some adjustments” to flight frequencies and using smaller planes on some routes, said Betsy Talton, spokeswoman for the Atlanta- based airline. She declined to specify the amount of capacity eliminated. Delta had 350 weekly flights to Mexico before the reductions.

United

UAL Corp.’s United, which flies to four Mexican cities, said it would reduce weekly round trip flights between the two countries to 24 from 61 in May, and to 52 from 90 in June. The changes start on May 5, the Chicago-based airline said.

US Airways, based in Tempe, Arizona, is trimming flights to Mexico by 38 percent, also by switching to some smaller aircraft and reducing frequencies. The airline will retain some service to all 12 cities it serves.

US Airways, which will reduce flights during two phases in May and June, said it will re-evaluate over the next few weeks whether more cuts are needed in July and August.

AirTran said today it has cut one weekly flight to Cancun from Atlanta and Baltimore-Washington, and that passengers can change itineraries to Mexico without penalty through May 15.

Continental rose 42 cents, or 4 percent, to $10.94 at 4:02 p.m. in New York Stock Exchange composite trading, while Delta added 25 cents, or 4.1 percent, to $6.42 and AirTran increased 16 cents to $7.11.

American Airlines

Canada’s two biggest airlines and tour operators in that country and Europe suspended service this week, as did Argentina and Cuba.

AMR Corp.’s American Airlines is monitoring and evaluating demand, spokesman Tim Smith said in an e-mail today. The carrier has extended to the end of May the grace period for changing flights without penalties. Flight attendants can wear both gloves and a mask while working flights into and out of all Mexico destinations, the workers’ union said today.

‘No One’ Booking Mexico

American “does not plan to make any changes unless given a directive from the CDC,” the Association of Professional Flight Attendants told its members in a message. “At this time, all flights are scheduled to depart regardless of flight loads.”

US Airways and United Airlines extended to May 31 the time passengers can change travel plans without penalty. US Airways said it’s had a “heavy” volume of calls from travelers about Mexico flights.

“Virtually no one is looking to book a new trip to Mexico right now,” said Matthew Jacob, an analyst at New York-based Majestic Research LLC. “Clearly it may take some time for people to feel comfortable traveling back to Mexico.”

Continental said it operated an average of 450 weekly departures from the U.S. to Mexico. The flu virus originated in Mexico, where schools have been closed and restaurants shut.

Air Canada, WestJet

“We were already experiencing soft market conditions due to the economy, and now our Mexico routes in particular have extra weakness,” Continental Chief Executive Officer Larry Kellner said in a statement.

The carrier will monitor demand and “adjust our capacity and costs accordingly,” he said. Using smaller jets on some routes means that while the number of seats flown to Mexico will drop by half, flights will fall 40 percent.

Continental’s weekly flights to Cancun will decline to 48 on May 4 from 98 now. The following week, the number will fall to 40, for a 59 percent reduction, Julie King, a spokeswoman, said in an interview. Weekly flights to Mexico City will slide to 78 on May 4 from 116 now, and to 60 on May 11 for a 48 percent drop.

The U.S. Centers for Disease Control and Prevention recommended on April 27 that nonessential travel to Mexico be avoided. It stopped short of advising consumers not to visit.

Air Canada and WestJet Airlines Ltd., Canada’s largest carriers, suspended Mexico service earlier this week, as did Montreal-based tour operator Transat A.T. Inc. TUI AG and Thomas Cook Group Plc, Europe’s biggest tour companies, also canceled flights.

To contact the reporters on this story: Mary Schlangenstein in Dallas at maryc.s@bloomberg.net; Mary Jane Credeur in Atlanta at mcredeur@bloomberg.net.

Last Updated: May 1, 2009 20:44 EDT