Part 91

Part 91 of the US Federal Aviation Regulations covers general operating and flight rules — how private, non-commercial flights are conducted, including most owner-flown and corporate flight-department operations. It is less prescriptive than the commercial rules because the operator isn't holding out transport for hire to the public.

Why it matters: Part 91 is the operating framework for private, non-commercial flying in the United States, and its equivalents exist worldwide. It offers the owner maximum flexibility — no commercial certificate, fewer prescriptive limits — with the trade-off that the owner carries responsibility for the standards a commercial operator would be forced to meet.

The boundary that matters is compensation: carrying paying passengers generally moves the operation out of Part 91 into commercial rules, and regulators police disguised charter seriously. Owners who let their aircraft earn money must do it through a properly certificated operator rather than informally.