The board of directors at Northwest Airlines plans to meet this morning to determine whether the airline should file for bankruptcy. The carrier has passenger hubs in Minneapolis, Memphis and Detroit. Northwest says it chose not to make 42 (m) million dollars in debt payments recently -- suggesting that the carrier is conserving its cash ahead of a potential bankruptcy filing. Bankruptcy worries sliced more than half the value off Northwest shares yesterday. Meanwhile, Northwest mechanics are in their fourth week of a strike, and the airline has begun making permanent hires of some replacement workers.