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Friday, January 1, 2010

The ABCs of ADS-B

By Chris Baur

Several recent events involving air traffic control surveillance come to mind. They involved aircraft not in radio contact with ATC. During the episode involving Northwest Airlines 188 (NW188), air traffic controllers surveilled an aircraft they could not communicate with for 90 minutes. Aside from the lack of communication and its unpredictable flight path when it overflew its destination by 150 miles, airspace was protected around this aircraft. Even though controllers could not communicate with the aircraft, they were able to avert tragedy.

The other event involved a mid-air collision between a sightseeing helicopter and a small single engine airplane operating in VFR conditions inside the Hudson River exclusion zone in New York City. It would appear ADS-B implementation for helicopter operations in New York City (and elsewhere) may receive a renewed sense of urgency. Another mid-air collision occurred recently between a Coast Guard C-130 and a Marine Corps helicopter near San Diego, Calif. Would ADS-B have made a difference?

ADS-B Out or automatic dependent surveillance–broadcast is one of the cornerstones in the FAA’s plans for NextGen. The cornerstones are known as CNS or communications, navigation and surveillance. It is the surveillance portion that involves ADS and radar. Terrestrial-based radar has been around since the 1930s. Depending on the ATC facility you are working with, radar has approximate 6–12 second latency, with 12 seconds on average for enroute radar, and six seconds for a terminal facility. Aircraft are often managed by where they were, not where they are. Radar is also dependant on line-of-site between the transmitter and the aircraft, creating expanses of airspace that are under-utilized. Until recently, this had been true for Alaska and the Gulf of Mexico. ADS-B can update as quickly as one second, providing superior surveillance for a variety of aircraft operations such as closely spaced simultaneous instrument approaches or WAAS LPV approaches to heliports. ADS-B Out uses GPS to determine the aircraft’s position, which is communicated to the transponder and broadcast to nearby aircraft as well as to the FAA via a network of ground stations.

ADS-B In provides a host of services, such as TIS-B and FIS-B. Traffic information service–broadcast (TIS-B) will provide participating aircraft traffic information from a variety of ADS-B and radar sources during the transition to ADS-B. Eventually TIS-B will be decommissioned when all aircraft are ADS-B compliant.

Flight information service–broadcast (FIS-B) will provide pilots with in-flight weather services such as atmospheric information and graphics such as NEXRAD images, PIREPS, and NOTAM service.

The first successful domestic ADS-B project was Alaska’s Capstone Project beginning in 1999 to address the needs of flight operators in Alaska. Capstone was so successful that in January 2007, it was folded into the Surveillance and Broadcast Services (SBS) program. According to Jim Cieplak, former Capstone program principal system engineer, Capstone can be attributed with reducing accidents by 47 percent during its tenure. Ultimately, 128 fixed- and 32 rotary wing aircraft were equipped with government-supplied avionics.

FAA manager of Central Service Area Surveillance & Broadcast Services, Jim Linney, says the helicopter ADS-B project for the Gulf of Mexico (GOMEX) has all of the platform installations needed for initial operation complete, with four additional sites being installed to expand coverage even further south. This covers an area 250 miles by 500 miles, shared by several different regulating states. The GOMEX operational testing began this fall with participating ADS-B avionics manufacturers, FAA aircraft and University Partners. The project’s plan is to become fully operational in December 2009, providing surveillance over all GOMEX oil rigs at 3000 feet and much lower in most places, including to the surface within line of sight where the 21 radio stations are placed. Operators are expecting to see a savings of 20 minutes per flight segment by having the ability to navigate directly vs. the current grid system. Additionally, since ADS-B equipped aircraft will be seen by FAA air traffic control, the FAA will have greater capacity for IFR traffic, which will reduce delays on the ground or offshore platforms. “The change in the level of service provided to the helicopters serving the oil and gas operations offshore will be dramatic,” said Jim Linney. “It’s a very important key site for the FAA national program and we are very excited to be united in partnership with this industry, bringing a new level of safety and efficiency to the Gulf of Mexico offshore community.”

ADS-B Out & In is an important part of NextGen for aircraft of all sizes, but especially helicopters. The FAA has dozens of radios deployed throughout the U.S. and plans to have the entire country covered by 2013. By using satellites to determine position, it can provide accurate positioning to the surface, over any terrain. It will also provide real-time traffic information and weather services, perhaps preventing another mid-air catastrophe.

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