Aviation: Satellites for Speedy Skies

By David Talbot

In 2007, 769 million passengers flew in the United States--a 72 percent increase over 20 years ago. But the world's radar-based air traffic control system, which hasn't changed much since the 1950s, is having difficulty keeping up. Around busy airports, controllers keep planes locked in constrained flight patterns with generous spacing margins for safety, because most radar systems "paint" planes only once every four seconds. These margins cause delays during bad weather or crowded conditions.

Credit: Tommy McCall

To add capacity, the United States is rolling out a new satellite-based air traffic control system, the key element of which is called Automatic Dependent Surveillance-Broadcast, or ADS-B. (Other nations are also beginning to adopt the technology.) By 2020, most planes will be required to carry a cockpit gadget that continuously broadcasts their GPS-derived location, altitude, and speed. Initially, this information will flow to ground-based controllers, allowing more precise instructions.

Eventually, all planes will also receive each other's position data. Onboard computers will let pilots chart course adjustments without having to consult air traffic control, and they will be able to fly closer together. "It will allow airplanes to line themselves up at the right spacing so controllers don't have to put in additional delays," says John Hansman, director of the International Center for Air Transportation at MIT.

The benefits will be even greater where there is no radar coverage, such as over the open ocean. Planes exiting radar coverage are now required to maintain a 60-mile gap, but with ADS-B in place, that distance can be reduced.

UPS has been testing ADS-B at its global hub in Louisville, KY, where about 100 planes converge during a three-hour period every night. There, ADS-B enabled the number of landings per hour to increase by as much as 15 percent, decreased emissions associated with landings and takeoffs by 34 percent, and reduced noise pollution by 30 percent.