definition - Fixed-Base Operator. Fixed-base operator. A fixed-base operator (FBO) is a commercial business granted the right by an airport to operate on the airport and provide aeronautical services such as fueling, hangaring, tie-down and parking, aircraft rental, aircraft maintenance, flight instruction, etc. [1] In common practice, an FBO is a primary provider of support services to general aviation operators at a public-use airport either located on airport leasehold property or, in rare cases, adjacent to airport leasehold property as a ...