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Wednesday, August 1, 2007

Rotorcraft Report: Which ADS-B Technology Will You Use?

Sometime this month, the FAA should award an almost $2 billion contract for its nationwide, 500+ ground-station automatic dependent surveillance-broadcast (ADS-B) network to Lockheed Martin, ITT, or Raytheon.

Uniquely, the winner will build the stations to its own specifications, not the FAA’s, then design, install, operate, and maintain them for a service fee. Also uniquely, Raytheon’s bid is not what the FAA expected. That could determine the equipment installed in helicopters, particularly those flying in the Gulf of Mexico, which are to be among the new network’s earliest users in 2010.

ADS-B avionics transmit signal bursts (called ADS-B Out) every second, containing ID, altitude, GPS position, and other data. Ground stations receive and relay that data to air traffic controllers’ screens. The signals are also received by other ADS-B-equipped aircraft (and called ADS-B In) and displayed in their cockpits for local traffic awareness.

Extensive testing has thoroughly proven the system. There’s just one problem. While major airlines use the international, 1090-MHz ADS-B frequency, the FAA felt airline equipment was unsuitable for general aviation and developed cheaper, 978-MHz universal access transponders (UATs). Because they use different frequencies, airliners and GA aircraft can’t "see" each other.

Consequently, it was widely assumed the FAA’s new ground stations would incorporate both frequencies, "translating" GA’s 978 MHz signals into 1090 MHz formats, then uplinking them to airliners and vice versa, allowing everyone to see everyone else. Lockheed Martin and ITT are understood to have bid that approach. But Raytheon proposed that general aviation drop UATs and adopt 1090 MHz, using new, price-competitive avionics. Single-frequency ground stations and their life-cycle costs would be cheaper, an attraction for the FAA. Also, since UAT is only available in the U.S., 1090-MHz-equipped GA aircraft could use ADS-B worldwide. However, UATs carry aviation weather — a key Gulf of Mexico requirement — that, for technical reasons, 1090 MHz can’t. So Raytheon proposed using XM Radio for weather broadcasts.

For Gulf helicopter operators, therefore, the FAA’s choice of a contract winner will determine their future ADS-B technology. There are pluses and minuses. 1090 MHz supports worldwide ADS-B, but avionics cost, availability, and certification may be issues, while XM Radio weather must still be certified for commercial operations. On the other hand, 978-MHz UAT avionics could be more readily available, possibly cheaper under competitive pressure, and offer certified weather broadcasts, but with ADS-B operations restricted to the U.S. Choices, choices. — Callan James

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