US-FAA14 CFR 119.21

Commercial operators engaged in intrastate common carriage and direct air carriers

This regulation establishes which operating rules apply to commercial operators and direct air carriers based on their type of operation. If you're conducting commercial flights for hire, you must obtain certification and operations specifications under Part 119, Subpart C, then follow specific operating rules:

Domestic operations (within the continental U.S.): Part 121 rules apply, with a special exception allowing certain Alaska island routes to use flag operation rules instead
Flag operations (international or certain long-distance): Part 121 rules
Supplemental operations (charter flights): Part 121 rules, though the FAA may require domestic or flag rules instead
Commuter operations: Part 135 rules
On-demand operations: Part 135 rules

The regulation also permits operators to "upgrade" to more stringent rules with FAA authorization—commuter operators may use Part 121 domestic/flag rules, and on-demand operators may use supplemental rules. This matters because it determines your aircraft requirements, crew qualifications, maintenance standards, and operational procedures.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*

This is an original plain-English explanation for training and reference, not legal advice and not for navigation. Always rely on the current official rule linked above. Last reviewed June 20, 2026.