U.S. travel agencies in September processed 5.5 percent fewer air transactions than they did a year earlier, according to ARC,

marking the largest year-over-year decline for any month since April 2011. Total air sales including refunds and exchanges were down 5.1 percent to $6.62 billion. Domestic transactions and airfare sales in September fell by 6.3 percent and 5.9 percent, respectively. International transactions retreated by a smaller margin, down 3.3 percent year over year, while international airfare sales declined at faster rate, down 10.1 percent, according to ARC data.