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New ATC System To Rely On AT&T Cell Towers
longacre writes "The FAA has awarded the long-anticipated first contract for development of its NextGen air traffic control system: a $1.8 billion deal with ITT Corporation, beating out bids from aerospace heavyweights such as Raytheon and Lockheed Martin. ITT's design will make use of hundreds of specially modified AT&T cellular phone towers which, in addition to their normal communications duties, will relay an aircraft's position to air traffic controllers and other aircraft in real time. The initial contract is only enough to wire and test the so-called ADS-B system in the Philadelphia area and around the Gulf of Mexico — hooking up the rest of the country will take an estimated 20 years and $20 billion."
That is precisely what this (ADS-B) does. At the moment, when not in radar coverage, the pilot uses the radio to report his position which he reads from his GPS (or other instruments). ATC copy this down and track his movement from these position updates. Now the problem with this is that by the time he reads out the position and ATC copies it down, the aircraft has actually traveled several miles.
This is the start of the problem. You don't actually have a pinpoint position to work with. You actually have a circle of probability which is combination of equipment and reporting errors. You could fit a lot of planes on a 100 mile route if you only had to keep them a mile apart and you had constant, pinpoint instant updating position information.
After getting the position report, ATC now have an expanding bubble of possible positions the aircraft could actually occupy until they get the next voice update which might be 30 minutes hence. This could end up expanding to 30 miles wide and 120 miles long before it is updated again. (Updating resets the probability circle back to just a couple of miles again). To keep aircraft from colliding you have to separate the the great big probability of position areas, not just a couple of points. Two aircraft could occupy 200 miles of airspace and it is now full; room for no more.
ADS removes the pilot and the ATC from the position reporting chain. The aircraft equipment just codes and sends the position directly to the ATC equipment. The position then automagically just appears on the controller's screen (with a display note saying that it is ADS derived). In busy airspace these reports can be generated only seconds apart pulling that circular error of probability back in to only a couple of miles with each update. You can now fit 50 planes into the airspace where you might have put only a couple before.
RADAR does exactly the same thing as ADS. The ground equipment asks the plane where it is and it sends back a reflection (primary) or a coded pulse (secondary) which is then displayed on a controllers screen. The difference with ADS is that instead of an enormously expensive piece of ground equipment to decode and receive the signal it can all be done on a regular vhf/uhf radio. If you add another radio antenna to a cell tower nobody cares. You can also utilise the existing ground network to carry the signal back to the ATC centre. You don't have to pay techs to install and maintain your own proprietary equipment.
Try building a couple of hundred multi-million dollar radar dishes across the landscape and every kook, luny, luddite and portable Faraday cage wearing weirdo will be out to stop you and protect the speckled barn toad as a bonus.
The huge advantages of ADS are that it is accurate, cheap and has a small ground footprint. It can be adapted for long range (hf) and satellite updating for oceanic sectors. It's all win. If someone asks "what will do when it breaks?" Well look out he window, we're doing it now.