Use Em' If You Have Em'!

United used to let frequent-flier accounts lay dormant for three years before dumping them, which was the previous industry standard, according to news reports.

Cost-cutting is the obvious objective.

US Airways says it will also close mileage accounts that have been inactive for 18 months, as of the end of this month.

Southwest Airlines cancels any freebies that fliers do not use within 24 months. Holdouts like American Airlines are expected to take similar measures, experts say.

"The glory days of the frequent-flier programs are over," said Joe Schwieterman, transportation expert and professor at DePaul University. "With low fares so pervasive, they don't generate the loyalty they used to."

"We are trying to make the program better for our most loyal customers," said United spokeswoman Robin Urbanski. "This also reduces our frequent-flier liability."

Frequent flyer miles were started 25 years ago by American Airlines.

The objective: reward faithful passengers. They have proved in the past to be very successful, say industry experts.

More than 180 million people around the world belong to these programs, estimates Inside Flyer magazine. They are entitled to nearly 10 trillion miles.

Frequent-flier programs have changed over time, with the requirements for redeeming a free ticket becoming more stringent.

But the concept remains a sacred cow among fliers and United risks provoking a customer backlash, said Britt Beemer, chairman and founder of America's Research Group, a consumer behavior and strategic marketing firm based in Charleston, S.C.