Part 121 (Operating Requirements: Domestic, Flag, and Supplemental Operations)

Part 121 is a set of regulations by the FAA that governs the operation of commercial air carriers in the U.S., including domestic, international, and supplemental (cargo-only) flights. It establishes safety standards for airline management, crew training, aircraft maintenance, passenger safety, and operational procedures. These rules ensure airlines operate reliably, maintain safety standards, and protect passengers and crew. In essence, Part 121 provides a comprehensive framework to promote consistent, safe airline practices across different types of commercial flights.