Future of air traffic is in orbit

FAA says satellite-based system will offer more precise navigation, improve safety

The future of air traffic control is satellite technology, not radar, according to the Federal Aviation Administration’s plan for a next-generation air transportation system.

A satellite-based program, known as Automatic Dependent Surveillance-Broadcast (ADS-B), would allow more planes to fly at the same time and improve safety, FAA officials said.

Studies suggest that today’s aviation system will be strained beyond capacity when demand triples in the coming years.

ADS-B will enable more precise navigation, permitting planes to fly closer to one another without colliding. The innovative system will broadcast Global Positioning System data directly from planes to neighboring aircraft and air traffic controllers. Radar, on the other hand, passively scans the airspace to locate flying planes.

For the first time, pilots — not just controllers — will have access to display screens that show details about nearby planes.

Full implementation of ADS-B is expected to take as long as 20 years. Onboard equipment and the necessary ground-station infrastructure will be installed in increments, while existing radar provides backup.

Radar is an outdated technology, the FAA says. Moving to ADS-B will let the agency eventually decommission some of the current ground radars. According to an FAA report, radar is imperfect and sometimes has trouble distinguishing airplanes from flocks of birds or patches of rain.

Radar’s constraints require planes to be separated by at least five miles in today’s National Airspace System, according to experts at the Air Transport Association (ATA), the airline trade group that lobbied for ADS-B. The system’s precision will allow planes to fly more closely without sacrificing safety, permitting increased airspace capacity.

Radar installations require large ground structures to house and support the equipment, according to the FAA. But ADS-B ground stations are the size of portable mini-refrigerators, so the FAA would not need to lease land to situate them. In addition, because the ground stations will be easier to place, they will provide better coverage to remote areas.

Increased airport capacity is another advantage of ADS-B. More accurate tracking will give air traffic controllers the ability to better manage the traffic arriving at and departing from congested airports. More planes will be able to fly from airports than before.

Currently, the ADS-B program is conceptual. Last September, the FAA officially committed to establishing it as the heart of the next-generation air traffic control system. The FAA has conducted operational evaluations in Alaska and the Ohio Valley.

For fiscal 2007, the FAA reserved $80 million to begin initial implementation of ADS-B in the National Airspace System. The FAA plans to let vendors install the ADS-B equipment and then lease services from the vendors — similar to how the agency currently buys telecommunications services.

ATA officials said airlines would embrace ADS-B enhancements only if the projected benefits materialize at a reasonable cost.

“While the concept of ADS-B is promising, its feasibility will be dictated by a detailed business case that reflects all costs and benefits, whether they apply to system users or the FAA,” experts from ATA’s operational and safety team wrote in an issue brief.

A number of challenges must also be addressed, ATA said. Chief among them are international interoperability, frequency capacity, navigation system redundancy and finding sources of position sensors.

The National Air Traffic Controllers Association, an FAA employee union, is also in favor of ADS-B but doesn’t want the system to replace radar anytime soon.

“To put our eggs in one basket and get rid of radar is foolish, and at the worst, it’s reckless,” said Doug Fralick, director of safety and technology at NATCA. “Our argument all along is that it doesn’t matter what system you put in place. The constraints on the system have always been severe-type weather and the limitations airports place on the traffic. The system is not the problem. They can go ahead [and] spend a lot of money, but in 2020 they are still going to have the same problems they have today.”

Fralick is urging a gradual, limited phase-out of radars.

Fralick also said the FAA should be more realistic about the benefits of ADS-B. FAA officials have said some of the responsibility for keeping safe distances between aircraft will shift from air traffic controllers to pilots, who will have cockpit displays that pinpoint all air traffic around them, along with local weather information.

Fralick said transferring more responsibilities to pilots means they will have to multitask. If that happens, air traffic controllers should not be held accountable for what happens as a result of the added demand on pilots, he said.

“You’re putting a burden on that pilot that he doesn’t have today,” Fralick said. “You can’t expect the controller to be liable for the separation [between planes] if you’ve changed the responsibility to the pilot.”

ADS-B may not be as expensive as radar for the FAA, but the new technology will be more expensive for airlines, he added. Today’s planes are not equipped with the necessary technology to interact with the system.

Despite the issues the FAA faces, Fralick said he thinks ADS-B will be deployed and should be. “It’s basically a good thing, but we have to do it right,” he said. “Don’t expect miracles because you put a new system out there. That’s fantasy.”

How Automatic Dependent Surveillance-Broadcast works

The Federal Aviation Administration’s future air traffic control system, Automatic Dependent Surveillance-Broadcast, may not depend on radar to track airplanes.

Instead, it might use Global Positioning System transponders installed in planes. The transponders determine the aircraft’s precise position in the sky.

The position is converted into a digital code and combined with other data from the aircraft’s flight monitoring system, such as the plane type, its speed and whether it is turning, ascending or descending. This digital information broadcasts to aircraft equipped to receive the data and to air traffic control ground stations every second.

Pilots see the information on traffic display screens in their cockpits while air traffic controllers see the same information on their displays.

Modern radar surveillance sends position information to air traffic controllers every 4.6 seconds, according to experts at the Air Transport Association, the airline trade group that lobbied for ADS-B. Such infrequent updates and the nature of the technology limit radar’s accuracy.

— Aliya Sternstein

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