ATLANTA (AP) Delta Air Lines said on Thursday it will adopt a popular feature of Northwest Airlines' frequent-flier program, as it aims to merge the two reward systems by the end of 2009.

Delta will allow its travelers to qualify for elite status by flying a certain number of segments, in addition to flying enough miles. The segment rule comes from Northwest, which flies many short routes around the Midwest that connect through its hubs. So, a single flight from, say, Minot, N.D., to New York with a stop in Minneapolis would be two segments.

Delta said the new rule will begin Jan. 1. Delta acquired Northwest in a deal that closed Oct. 29 and is working to integrate the two carriers over the next year to two.

Delta said it will add a third tier to Northwest WorldPerks awards. Northwest currently has two tiers for domestic travel, with tickets generally available for 25,000 miles and 50,000 miles. Delta's tiers for domestic travel are 25,000, 40,000, and 60,000 miles.

Delta also said all its frequent fliers will continue to earn at least 500 miles per flight, even when their flight is shorter. Some airlines have begun awarding the actual miles for short flights.

Delta travelers who have both its SkyMiles accounts and Northwest's WorldPerks accounts will be able to transfer miles between them beginning early next year. The carrier expects to merge the two programs entirely late next year.

Delta shares rose 14 cents, or 1.6 percent, to $8.88 Thursday.

(Copyright 2008 by The Associated Press. All Rights Reserved.)