Definition
Commercial aviation companies that operate under either Part 135 or Part 121 of the Federal Aviation Regulations. Part 135 governs commuter and on-demand operations, such as charter flights, air taxi services, and smaller scheduled commuter airlines. Part 121 governs scheduled air carriers operating larger aircraft, which includes the major and regional airlines. Both sets of rules impose stricter operational, training, maintenance, and crew qualification standards than those required of private pilots flying under Part 91.
Plain English
Companies that fly people or cargo for hire under specific FAA rulebooks. Part 135 covers charter and small commuter operations. Part 121 covers the airlines. Both have tougher rules than private flying.
Context Anchor
Seen in discussions of flight simulation training devices, especially when describing training programs used by airlines, charter companies, and other commercial operators.
Derivation
The numbers refer to the part numbers in Title 14 of the Code of Federal Regulations, where the FAA's rules are organized. Part 91 covers general flying, Part 135 covers charter and commuter work, and Part 121 covers scheduled airlines. Higher complexity of operation generally means a different rulebook.
Why Pilots Care
Determines the approved training programs, simulator credits, and qualification standards their pilots must follow.
Intuition Check
Do not read “part” as an aircraft component here. In this term, “part” means a numbered section of FAA rules, and “operator” usually means the company running the flights, not just the pilot flying the airplane.
Example Sentence 1
After earning her commercial certificate, she took a job with a Part 135 charter operator flying business clients in a light twin.
Example Sentence 2
The handbook explains how simulation devices satisfy qualification standards for Part 135/121 operators.