14 CFR Part 121

14 CFR Part 121 refers to the regulations set by the Federal Aviation Administration (FAA) in the United States that govern scheduled air carriers, including airlines. These rules ensure the safety, operational standards, aircraft maintenance, crew requirements, and passenger treatment for commercial flights. Key components include stringent aircraft inspection protocols, crew training requirements, and protocols for handling emergencies. Essentially, Part 121 establishes the guidelines that commercial airlines must follow to operate safely and efficiently, ensuring passenger safety and reliable service.