Air-Traffic Control Is in the Midst of a Major Change
Shift from radar to GPS should make tracking faster and more accurate, allowing more planes in the air
Since World War II, air-traffic controllers have used radar to keep track of aircraft.
But as of Jan. 1, most planes and helicopters flying in the U.S. must be equipped with transponders that allow their movements to be traced with GPS coordinates.
The deadline caused a flurry of upgrades last year as operators who hadn’t yet complied with the mandate rushed to equip their aircraft in time.
Now, more than 100,000 commercial and general aviation aircraft have the transponders, according to the Federal Aviation Administration, including nearly all commercial aircraft and an estimated 60% of general aviation aircraft that need it.
“If you’re flying an antique plane in the middle of Ohio, you don’t have to have it,” said John Zimmerman, vice president of Sporty’s Pilot Shop, an Ohio retailer and flight school.
The U.S. controls 29.4 million square miles of airspace, including all of the U.S., large portions of the Atlantic and Pacific oceans and the Gulf of Mexico. The FAA mandate primarily applies to Class A airspace, which is 18,000 feet or more above sea level; Class B airspace, the areas surrounding the nation’s busiest airports; Class C airspace, the areas around smaller regional airports; and above 10,000 feet in Class E, the most common airspace.
LaGuardia Airport in New York is Class B. Richmond International Airport in Virginia is Class C.
The new tracking system is faster and more accurate than radar, but it also fundamentally changes how air-traffic control works. And although the technology makes it possible to monitor aircraft over the ocean and other areas beyond the reach of radar, the U.S. isn’t yet using the satellite-based system that provides this capability.
Canada and the U.K., working with the American company Aireon, deployed satellite surveillance for their aircraft last year, and the U.S. will begin testing it in March. But for now, the FAA relies on ground stations equipped with the new technology, as well as old-fashioned radar ground stations, which won’t be abandoned completely.
“It’s a new jump in technology, and it requires a lot of analysis to understand the limits,” said David Gray, acting deputy director for the FAA’s Surveillance Services Directorate, referring to the FAA’s assessment of the satellite system. “Before we make a big investment, we need to know how to incorporate it into the tools air-traffic control uses to make them more efficient.”
For radar surveillance, the FAA maintains several hundred ground stations across the country that bounce radio signals off an aircraft, listen for the return signal and then calculate the aircraft’s position. Over the ocean when aircraft are beyond the range of radar surveillance, they periodically report their positions.
“If you fly to Europe or Asia, you think you are being tracked, because you see the map on the seat in front of you,” said Don Thoma, chief executive of Aireon. “The pilot knows where you are, and you know where you are, but air-traffic control gets an update only every 15 minutes.”
With the new system—which is called automatic dependent surveillance-broadcast, or ADS-B—aircraft are equipped with transponders that continuously transmit the identification, location, altitude, velocity and heading of aircraft flying in controlled space.
ADS-B ground stations as well as a network of specially equipped satellites receive the information. Other aircraft can opt to receive the feed as well, allowing them to see what air-traffic controllers see, but the FAA only requires aircraft to broadcast the data for the benefit of the controllers.
“ADS-B is a pivot from air-traffic control determining the location of aircraft using their own equipment to an aircraft determining its own location and advising air-traffic control of that location,” said Mark Duell, vice president of FlightAware, a Houston-based company that offers free flight tracking of private and commercial aircraft.
The FAA anticipates that aircraft will be able to fly more direct routes, saving time and fuel, and controllers will be able to reduce the minimum separation distance between aircraft, increasing capacity in the nation’s airways.
“There are more than 1,500 flights a day in the corridor between North America and Europe,” Mr. Thoma said. “Until March last year, it didn’t have surveillance. For safety, planes would keep 40 to 80 nautical miles apart. You would get in a spot behind another plane and move in a conga line across the North Atlantic until you hit radar coverage.”
Satellite-based ADS-B would allow controllers to narrow that gap to 14 nautical miles, according to Aireon, allowing more planes to join the conga line. (Vertical separation has already been decreased in some airspace, nearly doubling capacity in those areas.)
But other limitations might restrict the flow.
“How many times have you landed and had to wait 20 minutes to find a gate?” Mr. Zimmerman said. “And a lot of times it’s a runway.”
You can pack as many airplanes as you can in the air, he said, but eventually, they have to find pavement.