Northwest Air offers frequent flier deal MINNEAPOLIS, March 18 (Reuters) - Northwest Airlines Corp. (NWAC), the No. 4 U.S. carrier, said it is allowing members of its frequent flier program to combine miles and cash for tickets. Northwest's "Cash & Miles" promotion lets U.S. members of its WorldPerks program combine as little as 5,000 miles and $159 cash, or 10,000 miles and $109 cash for round-trip travel within the United States or to Canada. Tickets through the program are available for purchase immediately through April 30, for travel from April 1 through June 6. A spokesman for Northwest said such offers typically crop up several times a year. They allow travelers who do not have enough miles in their account for a free round-trip ticket, generally 25,000 miles, to use some of their miles for travel. Nortwhest Air shares rose 16 cents to $19.84 on Nasdaq Monday.