BOSTON — Want a free plane ticket?
Pack yourself into a winged aluminum sardine can for 25,000 miles first.
That was the theory behind frequent-flier programs.
But recently airlines have greatly expanded the ways travelers can earn frequent-flier miles. At the same time, they've clamped down on people's ability to spend them, by increasing the miles needed to earn a ticket, imposing expiration dates on miles, and limiting free seats on popular flights.
All the new rules have created a mass of confusion for frequent fliers.
To figure out the best frequent-flier programs, "you have to become a scientist, a CPA, or a brain surgeon," says Tom Parsons, president of Best Fares Online, who has amassed more than 3.5 million frequent-flier miles.
Like Mr. Parsons, 33 million Americans count themselves frequent fliers, and most join several mileage programs.
But are they worth it?
That depends on how you accumulate the miles and how you spend them.
"Often when you look back at all the tickets you've paid full price for to get that free ticket, it can be astonishing," says James Ashurst, spokesman for the American Society of Travel Agents.
Frequent-flier programs were originally developed to promote customer loyalty.
But they've developed into something quite different: another big revenue stream for the airlines, and a free-for-all among passengers vying for free seats.
One of the biggest problems is that airlines don't offer enough free seats to popular destinations to accommodate all the customers earning miles, says Mr. Parsons.
Mr. Ashurst agrees. He calls it "disingenuous for airlines to promote programs, when there aren't enough seats to go around."
On average, airlines give away 8 percent of their seats to frequent fliers.
But that average doesn't tell much. They could be 1 percent of seats between Los Angeles and Honolulu at Christmas and 25 percent from Dallas to Pittsburgh in February, Parsons says.
So if you're going to Hawaii for Christmas, you may have to call for reservations at 12:01 a.m. December 26th the year before. But even that may not work.
"Some people call a year in advance and [still] can't get seats," Parsons says. Tickets can't be reserved more than a year ahead.
Airlines don't have to say how many seats they set aside, and Parsons believes Congress should make them. Then passengers could choose the frequent-flier program that reserves the most seats on the route they fly most often.
When former Transportation Secretary Federico Pea promised an investigation into frequent-flier programs, "every airline out there, other than Southwest, was knocking at the knees," Parsons says.
"If there's anything that's becoming a travel scam, it's frequent-flier miles," he says.
The biggest problem with frequent-flier programs is how often airlines change the rules.
It's what keeps businesses like Best Fares Online and its rival Inside Flyer going, says Inside Flyer president Randy Petersen.
These two magazines, at least one book, and several computer programs have emerged to help sort through the confusion.
The main complaint Mr. Petersen hears is that airlines change the rules in mid-stream, such as when United Airlines recently began terminating miles more than three years old. Passengers saving up miles lost ground.
Northwest and American also terminate miles after three years. So if you're looking for a free 25,000-mile ticket, you'd better rack up those miles fast.
Other programs keep old miles active as long as you fly at least once every 18 months or three years.
The programs used to appeal primarily to business travelers, since leisure travelers couldn't build up miles fast enough to earn free tickets.
But some business travelers are having a harder time getting frequent-flier awards, because many of the small businesses springing up today make employees that travel on business turn over miles to the company.
Most large companies, though, see frequent-flier miles as incentives for employees to travel to offset the hassle of being away from home.
In the end, frequent-flier programs designed to inspire loyalty can entice customers to pay more for regular tickets on an airline they can build miles on.
So what's the best way to go? "Always buy the cheapest tickets and join all the programs," says Petersen.
Two years ago, he advised consumers to stick to two or three, because it was too hard to build up miles in any more programs.
But with all the new, nonflight ways to earn miles, there's no excuse not to be a member of several programs, he says.
If you fly only two or three times a year, join a program with miles that don't expire.
Consumer Reports magazine recommends using frequent-flier rewards only for cross-country or longer flights; they don't pay for themselves on short ones.
Other good values are discount companion tickets, usually $99, or upgrades to first or business class, although American Airlines recently increased the cost of these upgrades beyond the cost of free tickets.
Judge frequent-flier programs by how many free seats they reserve. Frequent fliers can earn miles by charging bills on their credit cards staying in certain hotels, parking, buying gas, flowers, or even homes.
But watch out for extra costs on these items, such as big annual credit-card fees, to pay for the frequent-flier miles.
Pick mileage-building programs, such as credit cards, by how many miles they give you per dollar spent, and how much they cost you.
Several airlines let you share frequent-flier miles. So you can build up miles on several carriers or with their credit cards, and pool them for one free ticket.