Applicability

Who Must Follow Part 121

Part 121 contains the operating rules for scheduled airlines and certain commercial operators. It applies to anyone holding (or required to hold) an Air Carrier Certificate or Operating Certificate under Part 119, covering their domestic, flag, and supplemental operations.

The regulation extends beyond just the airline itself—it also governs all employees and contractors working for these certificate holders, including maintenance personnel. Anyone on board an aircraft operating under Part 121 must comply with these rules, as must applicants conducting proving tests for new certificates.

A specific provision addresses nonstop commercial air tours, requiring them to follow Part 121's drug and alcohol testing requirements. There's a limited exception allowing tour operators without certificates to use non-drug-tested maintenance personnel for repairs when the nearest qualified facility is more than 50 nautical miles beyond the closest repair point, or for emergency repairs when the aircraft can't safely reach proper facilities.

*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.*