The average price to fly one mile increased 6 percent year over year in December, according to Air Transport Association data on the largest U.S.-based airlines

. Passenger revenue last month grew 9 percent year over year, making December the 12th consecutive month of such revenue growth and 2010 the first year since 2006 to witness such growth every month. ATA reported particular strength in international passenger business, with revenue up 16 percent year over year in December, while domestic revenue increased 6 percent.