Part 91 is the section of the Federal Aviation Regulations that provides general operating and flight rules for civil aircraft not receiving any compensation, or even reimbursement paid for carriage of passengers or cargo.
The U.S. Federal Aviation Administration (FAA) in the CFR Title 14 part 91 defines a Part 91 Operator. These are the regulations that define the operation of small non-commercial aircraft within the US, however, many other countries defer to these rules. These rules set conditions, such as weather, under which the aircraft may operate.
