### Question
How does the law define mainline carrier?


### Answer
Under *39 U.S.C. § 5402*, **mainline carrier** is defined as:

> a carrier operating aircraft under part 121 and certificated within the payload capacity requirements of subsection (g)(1)(D)(ii) on a given city pair route

#### Citation:
  - *39 U.S.C. § 5402*
  - Heading: **PART V-TRANSPORTATION OF MAIL > CHAPTER 54-TRANSPORTATION OF MAIL BY AIR**

