Flight departments handle all aspects of aircraft operation and maintenance. In the United States, flight-department aircraft operate under FAR 91 operating rules. A 2010 study by the United States National Business Aviation Association found that small and midsize companies that use private jets produce a 219% higher earnings growth rate than those that strictly use airlines. Charter companies Charter operators own or manage private jets for multiple clients. Like traditional flight departments, charter companies handle all aspects of aircraft operation and maintenance. However, they are not aligned with just one corporation. They manage aircraft for a private owner or corporation and also handle the sales of available flight time on the aircraft they own or manage. Maintenance services can also be provided. In the United States, business aircraft may be operated under either FAR 91 as private operations for the business purposes of the owner, or under FAR 135 of the Federal Aviation Regulations as commercial operations for the business purposes of a third party. One common arrangement for operational flexibility purposes is for the aircraft's owner to operate the aircraft under FAR 91 when needed for its own purposes, and to allow a third-party charter-manager to operate it under FAR 135 when the aircraft is needed for the business purposes of third parties (such as for other entities within the corporate group of the aircraft's owner). Aircraft charter brokers have entered the marketplace through the ease of setting up a website and business online. Aircraft charter operators are legally responsible for the safe operation of aircraft and charter brokers require no economic authority and are largely unregulated. The Department of Transportation requires that air charter brokers disclose to the consumer that they do not operate aircraft and cannot use terms like "our fleet of aircraft", "we operate", "our charter service" and others. Fractional ownership Since 1996 the term "fractional jet" has been used in connection with business aircraft owned by a consortium of companies. Under such arrangements, overhead costs such as flight crew, hangarage and maintenance are split among the users. Fractional ownership of aircraft involves an individual or corporation that pays an upfront equity share for the cost of an aircraft. If four parties are involved, a partner would pay one-fourth of the aircraft price (a "quarter share"). That partner is now an equity owner in that aircraft and can sell the equity position if necessary. This also