FORT WORTH, Texas — American Airlines wants to emphasize the "frequent" in frequent flier. Beginning Dec. 15, travelers who have not used their American Airlines frequent-flier accounts for the preceding 18 months will lose their accumulated miles.

With this change, the Fort Worth-based airline is essentially shortening its expiration time rules for inactive accounts. Previously, members of American's AAdvantage program had to generate some type of activity — typically by redeeming awards or earning new miles by flying American — every 36 months to prevent their accounts from expiring. With the change, that drops to just 18 months.

"From a consumer standpoint, this is really disappointing," said Tim Winship, publisher of the Web site www.FrequentFlier.com.

American follows several other carriers, including United Airlines and US Airways, that announced similar moves this year.

American spokesman Bill Sanez pointed out that customers don't necessarily need to book flights to earn more miles and keep their accounts active. American has a variety of partners, including credit cards, hotel chains, and even mortgage companies, that offer miles for using their services.