entitles the new owner to a certain number of hours of flight time on that aircraft, or any comparable aircraft in the fleet. Additional fees include monthly management fees and incidentals such as catering and ground transportation. In the United States, fractional-ownership operations may be regulated by either FAA part 91 or part 135. Other Operation Models Other operation models used by private jet hire companies include buying blocks of time in predetermined increments, pay as you fly and paying a flat rate for unlimited usage and access. Buying blocks of time in predetermined increments involves buying blocks of time in hours. This model usually depends on how many flight hours a client will be needing. Pay as you fly resembles the business model used by commercial airlines where a client only pays for a flight they use. The downside to this model is that clients find it difficult to secure flights because most private flights are usually booked in advance. Paying a flat rate for unlimited usage as the name implies, uses a business model where clients pay a flat rate, and then the jet is made available to them for the duration that payment lasts. This model makes it possible for a client to pay a certain amount for unlimited access and usage to a jet, or a fleet of jets for the duration. This model has been discontinued by most private jet hire companies because clients have exploited the usage in the past. This model now employs a fair usage policy. Surveillance With smaller equipment, long-range business aircraft can be modified as surveillance aircraft to perform specialized missions cost-effectively, from ground surveillance to maritime patrol: the , 6,000 nmi Bombardier Global 6000 is the platform for the USAF Northrop Grumman E-11A Battlefield Airborne Communications Node, the radar-carrying ground-surveillance Raytheon Sentinel for the UK Royal Air Force, and Saab's GlobalEye AEW&C carrying its Erieye AESA radar as UK's Marshall ADG basis for Elint/Sigint for the United Arab Emirates; it is also the base for the proposed Saab AB Swordfish MPA and the USAF Lockheed Martin J-Stars Recap battlefield-surveillance program, while IAI's ELI-3360 MPA is based on the Global 5000; The , 6,750 nmi Gulfstream G550 was selected for the IAI EL/W-2085 Conformal Airborne Early Warning AESA radar for Italy, Singapore and Israel (which also has IAI Sigint G550s) while L3 Technologies transfers the U.S. Compass Call electronic-attack system