Moments & Milestones: A Farewell to Radar
Produced in cooperation with the National Aeronautic Association
- By George C. Larson
- Air & Space magazine, July 2008
The judges who awarded this year’s Collier Trophy didn’t choose an airplane or its designers; they selected something that is more of a concept than a piece of hardware. Actual operational equipment for Automatic Dependent Surveillance-Broadcast (ADS-B) has only a toehold so far on the world’s air traffic management (ATM) systems. Still, the technology is so promising that almost everyone in the industry favors ADS-B to replace the radar-based systems that have served ATM so well since the Federal Aviation Agency was formed in 1958 to oversee air traffic safety.
In its day, radar was regarded as the near-miraculous technology that had helped the Allies win World War II. It displayed aircraft position night or day in all weather, enabling controllers to radio the information and instructions to pilots. But radar is expensive and hard to maintain. It can’t reach past the horizon, and high terrain blocks it, creating blind spots for controllers. To scan the entire sky, its antennas have to be rotated by electric motors, and its electronics are complex. Radar was improved by the addition of aircraft-mounted transponders that transmit a four-digit identity code and altitude in hundreds of feet, enabling controllers to identify whose blip was whose and keep the traffic separated. Computers that processed the radar and data helped even more.
But the current system has two remaining drawbacks: Information has to be passed by voice and the information is in the wrong place—on a radar screen on the ground. When airspace is congested, voice communication is a clumsy way to move information. There are simply too many people talking at once. Every call by a controller or pilot has to be acknowledged to ensure it was heard. If two pilots key their mikes simultaneously, the calls are blocked, and at busy terminals this happens all the time, forcing callers to repeat themselves.
In ADS-B, satellite-borne transceivers use GPS and other navigation aids (such as an Inertial Reference Unit) to obtain aircraft position information, then transmit it to the electronic displays of everybody who needs it—not just air traffic controllers but other aircraft in the area as well (see “How Things Work: Aircraft Identification,” Oct./Nov. 2006). And the system does this without requiring any voice communication, so in the future, the only times controllers will need to talk to a pilot by radio is when they see something abnormal. There are no blind spots, and the hardware involved (perhaps with the exception of the satellite systems) is simple and cheap and has no moving parts. And the transceivers, flying over the oceans and both poles, will be able to track aircraft in locations no radar could ever reach.
ADS-B is already operating in China, Australia, and other areas with less extensive or entrenched radar-based systems, and is also being used by general aviation pilots in Alaska and air transport carriers in the Ohio River Valley; the FAA says that by the end of next year, the technology will be providing tracking information in the Gulf of Mexico, where dozens of helicopters fly workers to their oil rig platforms.
You can learn more about ADS-B at the Web site United States and other details.
—George C. Larson, Member, NAA