Definition
Part 121 is the section of Title 14 of the Code of Federal Regulations (14 CFR Part 121) that governs the operation of scheduled and supplemental air carriers, primarily large airlines flying passengers and cargo for hire. It sets the certification, training, equipment, maintenance, and operational standards that these carriers must meet, including crew qualifications, flight and duty time limits, and the use of approved training programs and flight simulators.
Plain English
Part 121 is the set of FAA rules that the major airlines fly under. It covers how they train their pilots, maintain their aircraft, and run their day-to-day operations.
Context Anchor
Seen when FAA material discusses airline training programs, pilot checks, and the approved use of simulators or flight training devices.
Derivation
The name simply refers to the numbered part of the federal regulations: Part 121 of Title 14 CFR. The FAA organizes its rules by numbered parts, with each part covering a specific area of aviation. Knowing the number lets pilots quickly find or cite the right rules.
Why Pilots Care
Airline pilots and instructors must meet Part 121 training standards, which directly determine what simulators can be used for and how much credit they receive toward certification.
Analogy
Think of part 121 like a chapter number in a large rulebook. Saying “part 121” points you to the airline-operations chapter, not to a single rule by itself.
Intuition Check
Do not read “part” as an aircraft component here. In this context, “part 121” means a numbered section of federal aviation regulations.
Example Sentence 1
After earning her ATP, she was hired by a regional airline operating under Part 121.
Example Sentence 2
Instructors checked the Part 121 requirements before logging simulator time toward a captain upgrade.