14 CFR § 121.480

Certificate holders conducting operations with aircraft having a passenger seat configuration of 30 seats or fewer, excluding each crewmember seat, and a payload capacity of 7,500 pounds or less, may comply with the applicable requirements of §§ 135.261 through 135.273 of this chapter.

A certificate holder may apply the flightcrew member flight time and duty limitations and requirements of part 117 of this chapter. A certificate holder may choose to apply part 117 to its—

All-cargo operations conducted under contract to a U.S. government agency.

All-cargo operations not conducted under contract to a U.S. Government agency,

A certificate holder may elect to treat operations in paragraphs (b)(1) and (b) (2) of this section differently but, once having decided to conduct those operations under part 117, may not segregate those operations between this subpart and part 117.