Travelers know it's not necessary to board an airplane to rack up frequent-flier miles. They've long been using airline-branded cards to buy gasoline, meals, computers and clothing, which slowly add to their bank of miles.

But spending has gone to extremes. Travelers are throwing down the plastic to cover college tuition, make mortgage payments, buy vehicles and even pay for funerals.

Some are finding that cosmetic surgery will get them airborne. Gerald Slawecki of Fort Washington, Md., charged a $20,000 face-lift for his wife, Constance, on his Continental Airlines co-branded MasterCard, giving him enough miles for two round-trip business-class tickets to St. Thomas.

Thanks to airline-branded cards, paying for home improvements can lead to get-away-from-home vacations. Carol Lane, an advertising writer in Washington, D.C., recently took out a home-equity line of credit to remodel her bathroom. But instead of paying for the new bathroom fixtures with the line, she used her United Airlines credit card and received 40,000 award miles. She then used her line of credit to pay off the credit-card bill.

The rush to accumulate miles comes at a time when it is harder than ever to use them. Some airlines have raised the number of miles needed for trips while reducing the number of U.S. destinations and flying smaller planes.

Frequent-flier guru Randy Petersen, publisher of Inside Flyer magazine, said travelers often have to book from six months to 10 months ahead to get an available seat to popular destinations such as Paris. Travelers interested in going to Europe next summer on frequent-flier miles, Petersen said, should begin booking by December.

Petersen said most airlines have formed code-share alliances with other carriers. For example, if a Delta Air Lines frequent flier can't get a free trip on that airline, there may be space available on its partners, Northwest or Continental. Or if a traveler can't find one on United Airlines, he or she could try its partner, US Airways.

Travelers like using airline-sponsored credit cards to build miles, Petersen said, because it frees them from having to fly one carrier repeatedly to bolster their accounts. Some airlines, such as United, Delta and Continental, allow users to gain "elite" status through their credit-card purchases. The higher the travelers' status within the airline's program, the fewer restrictions in redeeming the miles for free trips.

Some frequent fliers said the annual credit-card fees of $60 to $85, depending on the airline and the credit card, also make the cards less attractive. Marybeth Majka of Arlington, Va., said she has no trouble getting flights to such cities as Buffalo, N.Y., and Greenville, S.C. "But trying to get seats to St. Thomas or someplace I really want to go, forget it," she said. "I'm rethinking using these cards."

Airlines have tried to address frequent fliers' ire over the difficulty of redeeming miles. Last month, United Airlines launched its Mileage Plus Choices Visa card, which is similar to Capital One's No Hassle Miles card because it claims that earned miles can be redeemed for any flight, anytime, with no blackout dates or seat limitations. Delta has a similar deal with its co-branded American Express card.

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