U.S. scheduled airlines are classified by the government on the basis of the amount of revenue generated from operations. These classifications are major, national and regional.
All airlines hold two certificates from the federal government: a fitness certificate and an operating certificate. The Department of Transportation (DOT) issues fitness certificates - called certificates of public convenience and necessity - under it's statutory authority. Basically, the certificate establishes that the carrier has the financing and the management in place to provide scheduled service. The certificate typically authorizes both passenger and cargo service. Some airlines, however, obtain only cargo-service authority. Commuter airlines that use aircraft with a seating capacity of 60 or fewer seats or a maximum payload capacity of no more than 18,000 pounds can operate under the alternative authority of Part 298 of DOT's economic regulations.
Operating certificates, on the other hand, are issued by the Federal Aviation Administration (FAA) under Part 121 of the Federal Aviation Regulations (FARs), which spell out numerous requirements for operating aircraft with 10 or more seats. The requirements cover such things as the training of flight crews and aircraft maintenance programs. All majors, nationals and regionals operate with a Part 121 certificate. more >>