Definition
Part 125 is the section of Title 14 of the Code of Federal Regulations (14 CFR Part 125) that governs the operation of large airplanes — those with a seating capacity of 20 or more passengers or a maximum payload capacity of 6,000 pounds or more — when they are not operated under the air carrier rules of Part 121 or the on-demand rules of Part 135. It sets out certification, operating, and maintenance requirements for these aircraft, including private operators of large airplanes carrying their own personnel or property.
Plain English
Part 125 is the FAA rulebook that covers big airplanes (20+ seats or 6,000+ lb payload) when they aren't flying as scheduled airlines or charters. It tells operators how to be certified, how to operate the aircraft, and how to maintain it.
Context Anchor
Seen in FAA handbooks and procedure discussions when identifying which operating rules apply to a particular aircraft or operator.
Derivation
In FAA regulations, a “Part” is a numbered section of the aviation rules. “125” is the number assigned to this particular set of rules, so “Part 125” means the rule section labeled 125.
Why Pilots Care
Pilots and operators must follow Part 125 standards for crew qualifications, equipment, and procedures when conducting flights in large aircraft outside of scheduled commercial service.
Intuition Check
“Part” does not mean a physical piece of the airplane here. It means a numbered section of the FAA regulations.
Example Sentence 1
Because the company's corporate jet seats 24 passengers and isn't operated for hire, it falls under Part 125 rather than Part 91.
Example Sentence 2
Under Part 125 the flight crew completed the required training for the large jet they were operating.