American Airlines will join the ranks of other airlines in changing how travelers accumulate rewards miles.

On Tuesday, the airline announced a series of changes to its AAdvantage loyalty program, adjusting how travelers can earn rewards miles and what it takes to redeem them. Under the new rules, which will take effect in March, certain types of flights, such as first-class trips to Europe, will require more miles than they did before, while others, including business-class flights to the Caribbean or Central America, will require fewer rewards miles.

One of the biggest changes is that consumers will now earn rewards miles based on how much they pay for their flights and not how far they travel. In the move, American joins other major airlines including United, Delta and Southwest, which all issue rewards miles based on how much travelers spend.

AAdvantage members will now earn five miles for every dollar spent on base fare and carrier-imposed fees, excluding taxes and government-based fees. Elite-status members will earn more miles per dollar spent.

The shift might make it more difficult for travelers who find good deals on long flights to earn miles and may reward people who can afford to pay for first-class or business-class flights. “The only people who are earning more miles are the people who buy really expensive tickets,” said Scott Mackenzie, founder of Travel Codex, a travel blog that focuses on miles and loyalty programs.

Take a person who books a cross-country flight from New York City to Los Angeles for $350. Under the current system, the person would earn close to 5,000 rewards miles round-trip. But under the new program, that same flight would bring in only about 1,750 rewards miles.

The difference may not be so large on more expensive flights that cover long distances. American gives the example of a flight to London from Dallas, which is 9,502 miles round-trip and costs $1,894. Under the new system, AAdvantage members would earn 9,470 miles.

The amount of miles needed to book economy-class tickets in the United States or abroad will stay largely the same. But travelers will generally need more miles to book coveted first-class seats they might otherwise struggle to afford, Mackenzie said. Under the new award chart, U.S. travelers will need 85,000 miles to book a one-way first-class flight to Europe, up from the 62,500 miles required by the current award chart.

Travelers who want to redeem rewards miles under the current system need to book their trips by March 21. The actual travel can take place later.

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