Northwest Airlines

( NWAC) will lay off about 400 pilots in the coming months as it reduces mainline flights during its Chapter 11 restructuring.

Northwest informed its unit of the Air Line Pilots Association of those changes Thursday, according to the union's Web site.

The Eagan, Minn.-based airline, which along with

Delta Air Lines

(DAL) - Get Report

filed for bankruptcy protection Wednesday evening, told ALPA it will reduce mainline block flying hours by 13%. The resulting layoffs will begin Nov. 1.

A Northwest representative declined to comment on the disclosures by the pilots' union but noted the airline has already announced it would reduce its capacity in the fourth quarter by 5% to 6% from the year-earlier period. At the end of 2004, the carrier had 5,100 pilots represented by ALPA, according to company filings.

The term mainline refers to a network airline's standard routes on large passenger jets, which differ from smaller feeder flights typically contracted out to regional airlines.

The union pointed out the layoffs were the result of reduced flying levels and not contract changes.

Northwest is now seeking a total of $1.4 billion in annual savings from all its labor groups, a figure that includes $265 million in concessions ALPA made late last year. However, the airline is expected to ask pilots for more savings as it tries to use the bankruptcy process to extract new contracts from workers.

Northwest shares will likely be cancelled and rendered worthless if and when the airline emerges from bankruptcy, but they do still trade and were at 86 cents Friday.