Your best source is the US Govt's 'Office of Airline Information'. It states: "The OAI mission is to provide the U.S. government, DOT, and other users with uniform and comprehensive financial and market/traffic statistical economic data on individual air carrier (airline) operations and the air transportation industry."
see: http://www.bts.gov/oai/

Also, check out the main page of the "Bureau of Transportation Statistics" at: http://www.bts.gov/