In the Gulf of Mexico, there are two major operating aviation users: low altitude offshore and high altitude. The low altitude offshore operators are primarily helicopter fleets supporting the oil and gas exploration efforts; their traffic typically consists of 5,000 to 6,000 flights per day, most less than one hour in duration. In the high altitude regime, over 300 oceanic flights pass through the Gulf of Mexico. Offshore surveillance coverage in the Gulf of Mexico is currently limited due to remote, over-water operations. Implementation of primary or secondary radar to support surveillance coverage in the Gulf of Mexico is technically and economically difficult. Air traffic between the United States and destinations in the Caribbean, Mexico, and Central America has grown at a rate of over 8% per year over the last 12 years. Currently, flights that transit the Central Gulf of Mexico are subjected to oceanic separation standards in part because of a lack of direct pilot-controller communications, standardized aircraft navigation requirements, and limitations to radar surveillance. Air traffic traversing the Gulf of Mexico often must choose between accepting a ground delay, a reroute, or a less fuel-efficient altitude. An estimated 40% of the traffic in the non-radar airspace may not receive their requested altitude or route. However, if seamless surveillance and communication coverage were implemented in the Gulf of Mexico, aircraft separation standards may be reduced from the current oceanic standards to domestic enroute standards, thus reducing delays and improving aircraft safety. To improve surveillance coverage in the Gulf of Mexico for both the low altitude and high altitude users, the National Aeronautics and Space Administration (NASA) has initiated activities leading to deployment of alternative surveillance technology in the offshore area of the Gulf of Mexico. These technologies, multilateration and ADS-B, has significant potential to fill the lack of surveillance in the Gulf of Mexico. NASA conducted previous evaluations of multilateration and ADS-B for the low altitude offshore users recently. These evaluations demonstrated the feasibility of ADS-B and multilateration. NASA, along with the Federal Aviation Administration's (FAA) Safe Flight 21 Program Office are conducting evaluations to determine ADS-B, as well as wide area multilateration, performance over US controlled high altitude airspace in the Gulf of Mexico. To support this evaluation, a network of eight ground stations (Mode S extended squitter) has been installed from Texas to Florida with the Central Processing System located at the Houston ARTCC in Houston, TX. As part of this network, three ground stations have been installed approximately 200 NMI offshore in the Gulf of Mexico. This network provides almost entire coverage of US oceanic airspace in the Gulf of Mexico. Also as part of this evaluation, the network of ground stations provides wide area multilateration coverage as well (where 3 or more ground stations receive an aircraft's transponder reply). The multilateration coverage area provides surveillance for aircraft at FL240 and above. Three flight tests, using the FAA Tech Center's B727 and the NASA Gulfstream III aircraft, were conducted from January to March 2004. The results from these flight tests are presented in this paper, assessing the performance of ADS-B and wide area multilateration in the Gulf of Mexico.
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