Original URL: http://www.theregister.co.uk/2007/09/04/gps_satnav_air_traffic_for_america/

US in move towards GPS-based air traffic control

Onboard satnav data to replace scanning radar

By Lewis Page

Posted in Science, 4th September 2007 16:35 GMT


Current air traffic control systems worldwide use radar to detect and track aircraft: either "primary," in which radio pulses from the radar reflect back from the plane's skin, or "secondary," where a transponder emits a code or "squawk" in response to the radar transmission.

In either case, the controller's picture updates only as fast as the radar antenna can spin round, which typically means every six seconds or so. During that time a jet can travel a mile, and usually the radar location info isn't very precise either, which means that, in congested airspace, a substantial margin of error must be maintained. This in turn means fewer planes can move through a given amount of airspace, leading to delays.

Now, however, the Federal Aviation Administration (FAA) intends to move to a system called Automatic Dependent Surveillance-Broadcast (ADS-B), which will lay the groundwork for the Next Generation Air Transportation System, or NextGen.

Under ADS-B, each plane is fitted with GPS satellite navigation, and thus knows its own location precisely. This information will then be broadcast in real time to a ground network, updating every second. Controllers will have a much more accurate idea where all the aircraft are, which could potentially allow them to move planes through bottlenecks more quickly.

“This signals a new era of air traffic control,” according to FAA number-two, Bobby Sturgell. “ADS-B - and, in turn, NextGen - will attack the delay problem head on by dramatically increasing air traffic efficiency.”

ADS-B will also be a two-way street, allowing pilots to see full information on all the planes in the sky around them, just as controllers do. At the moment, most aircraft don't have a proper radar of their own, though they may have proximity warning systems or weather radars. For monitoring other planes, today's pilots are mostly dependent on ground controllers - or the limited capabilities of the naked eye.

"Along with air traffic displays, ADS-B will also give pilots graphical weather information, terrain maps and flight information... ADS-B is nearly 10 times more accurate than radar," according to the FAA release.

ADS-B will be especially useful where there aren't any ground radars or controllers, which is the case across much of the world's airspace.

"The ITT Team is proud to have been selected... for the transformation of the air transportation system," said ITT bigwig Steve Gaffney. "ITT and its premier team of industry partners are committed to working with the FAA to ensure this NextGen cornerstone program delivers its full potential."


Under the contract, ITT will be responsible for overall system integration and engineering. There are options included, too, for ITT to operate and maintain the system after deployment until 2025. With all options exercised, the deal could be worth up to $1.86bn.

ADS-B trials have been carried out among light-aircraft aviators in Alaska and heavier operators in Ohio. There is a not dissimilar international system in use for seagoing ships, too, called AIS. However, AIS works much more on the ship-to-ship model, as shipping traffic isn't commonly controlled outside rivers and harbours - certainly not to the level that aircraft are.

One criticism that has been levelled at AIS is that of security. It has been alleged that modern-day pirates and other miscreants make use of AIS transmissions to locate, track and target ships - especially where AIS data is disseminated over the internet. Such concerns might apply to ADS-B, too.

At the strategic level, heavier reliance on GPS arguably makes the USA more vulnerable to anti-satellite attacks of the sort that China, for instance, is known to be able to mount. That said, GPS is already fairly critical.

It's also possible to suggest that ADS-B would be easier to spoof than old-time radar systems. Persons of ill intent might tinker with ADS-B rigs to send false information, perhaps causing disruption. Aircraft might even be able to escape notice, if the existing radars were - in time - removed; though military air-defence kit would no doubt remain in place.

Many of the same criticisms could also be made regarding existing air-band voice radios, though, or squawk transmitters. (For instance, it's especially important when setting a code on an old-time squawk box not to set the one which means "I have been hijacked" by accident. Even more so these days, if you don't want to get shot down.)

Some might be pleased with ADS-B/NextGen, as it could be a step along the road to a "synthetic vision"-type infrastructure, which might allow suitably automated small aircraft to be handled by largely untrained pilots.

Such systems would be necessary if our flying cars - for which we've been waiting bloody forever - are to become practical and affordable - though it's scarcely the only hurdle to be cleared.

Air-traffic controllers' spokesmen were predictably sceptical about ADS-B, suggesting that it would be better to have more airports and hire more controllers. It's unlikely that ADS-B and NextGen would ever completely automate controllers out of a job, in the same way that pilots probably won't disappear from the flight deck. But the controllers could see their numbers cut very severely by automation in times to come.

"This program and what it represents is not the answer to flight delays and the congestion that has choked the whole air traffic system," said Doug Church of the National Air Traffic Controllers Association, quoted in a GovExec.com report.
