Talks aimed at ending a 9-day-old strike by pilots at Northwest Airlines Corp. that has shut down the nation's fourth-largest airline were recessed for two days without a direct meeting between the two sides. Instead, labor and management met for two days alone and with federal mediators, who shuttled between conference rooms to determine if formal negotiations could resume. About 6,200 pilots struck Northwest, which is based in St. Paul, Minn., Aug. 29 after almost two years of negotiations failed to yield a new contract. Unresolved issues include pay, job security, retirement terms and the duration of a new contract, a spokesman for the pilots' union said Sunday. Meanwhile, Northwest said it will waive many restrictions and fees for customers holding tickets on flights from now through Sept. 16 who wish to rebook their travel for later in the month or later this fall.