AIRLINES

Airline Reservation Centers Flooded With Calls: The centers were swamped as major carriers expanded the scope of a summer air fare sale. American Airlines and other carriers, which had initially matched a 30% fare cut by Northwest Airlines only on competing routes, expanded the sale to all domestic destinations. The lower fares also were extended to June 30. Demand for the discount tickets--which can be used for travel any time through Sept. 30--sparked a 60% increase in customer calls to United Airlines.