For an extra $15, Northwest Airlines Corp. will sell coach passengers a few more inches of legroom.

Starting Tuesday, Northwest will ask passengers on most domestic flights if they're interested in paying extra for certain prime seats in coach — exit-row seats or aisle seats near the front of the cabin.

The "Coach Choice" program will involve about 5 percent of seats on Northwest's domestic flights.

Northwest's exit-row seats can have 10 to 13 inches of extra leg room. And many air travelers prefer the convenience and extra elbow room of aisle seats to center and window seats.

Jim Cron, vice president of passenger marketing and sales, said Northwest is trying to give more flexibility to passengers who book late. They're often the travelers who pay full fare, but often find that the only seats left are middle seats in the back of the plane because leisure travelers who booked early reserved the best seats.

Northwest, the nation's fourth-largest airline, has been operating under Chapter 11 bankruptcy protection since September. Cron acknowledged the carrier is scouting ways to increase revenue but declined to estimate how much the $15 fee might generate.

UAL Corp.'s United Airlines (UAUA) and Virgin Atlantic Airways, a unit of Virgin Group Ltd., already assess a premium for certain desirable coach seats.