What type of operations are regulated under 14 CFR Part 121?

Scheduled air carriers are regulated under 14 CFR Part 121 because this part specifically governs the operation of commercial air carriers that conduct scheduled passenger and cargo flights. Part 121 outlines the requirements for operating commercial air transportation services, including the necessary operational protocols, maintenance standards, and safety regulations that these carriers must adhere to in order to ensure the safety of their operations and the public.

In contrast, air charter or air taxi operations typically fall under different regulations, such as Part 135, which is designed for on-demand operations rather than scheduled flights. General aviation flights and private pilot operations likewise fall outside the scope of Part 121, as these types of flying do not involve the same level of regulatory oversight required for scheduled air carriers. Parts 91 and 135, for instance, govern general aviation activities and commercial operations that do not operate scheduled services, respectively. Thus, the focus of Part 121 is specifically on measures that maintain safety in a structured and predictable flight schedule.