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What You Won’t Get From ADS-B

May 16, 2011

The FAA is beating the drum urging all of us to equip our airplanes now with the ADS-B (automatic dependent surveillance-broadcast) equipment that is the backbone of the NextGen air traffic control system. In short, ADS-B continuously broadcasts to all other airplanes, and to FAA controllers, the location, altitude and velocity of each aircraft.

Instead of a radar on the ground detecting the location of each aircraft, ADS-B will broadcast to all the aircraft’s position, altitude and so on. With the position fixing based on the common navigation grid of GPS, and with a new position broadcast once each second, ADS-B will provide a much more accurate and reliable location and flight track of each aircraft than ground based radar can.

But switching to ADS-B transfers many of the costs of equipping the ATC system from the ground to the cockpit. With ADS-B the FAA will no longer have to build and operate expensive radars, but airplane owners will have to pay to install and maintain ADS-B equipment. As you can imagine, many of us are not anxious to pay for something—air traffic service—that has been government funded for decades. Yes, we all own and maintain transponders to communicate with the radar, but a transponder is a minor expense compared to a full-up ADS-B installation.

To try to make ADS-B and NextGen more attractive to airplane owners the FAA offers to send up weather information and a plot of all other aircraft in your area for free over the ADS-B data link. Most of us already have a traffic alerting system, and in larger or turbine airplanes, a traffic system is required. And most of us also have the equipment to receive weather via satellite either from XM or Sirius. So, the best the FAA can offer is free weather instead of paying the satellite subscription, and a more accurate display of traffic than an airborne system can provide. That’s not much.

But the FAA’s selling of ADS-B as a source for weather and traffic is even more disingenuous than it appears. The reason is that ADS-B is designed to operate on two different frequencies and only one of those frequencies can receive free traffic and weather.

The system that gets the free stuff is called the universal access transceiver (UAT) and it operates on 978 MHz. This is the network that you have read about that is in use now in Alaska, over the Gulf of Mexico, by UPS cargo airplanes, and by several major flight schools. The UAT has enough bandwidth for the weather, traffic, notams and such to be sent up, along with the transmitter in the airplane broadcasting the aircraft position information.

The other ADS-B frequency is 1090 MHZ, the frequency used by all transponders, including the Mode-S units that are part of TCAS equipment. The 1090 frequency is very crowded, as you can imagine, with every transponder and ground based radar broadcasting on that frequency, as well as TCAS units exchanging information. There is no room left on 1090 to send any additional information. And some of us even wonder if there is enough bandwidth on 1090 for the addition of ADS-B, plus the transponders that we all must continue to have operating after ADS-B becomes law in 2020.

So, if you choose 1090 for your ADS-B solution, you won’t get any of the free information the FAA touts. And here is the real poke in the eye—any airplane that operates above 18,000 feet must use 1090. So all turbine airplanes and even pressurized or turbocharged pistons must use 1090 and thus will not get any of the free services the FAA talks about.

It’s something of a bait and switch by the FAA. The agency doesn’t always make it clear when selling the benefits of ADS-B that many airplanes cannot use those benefits.

The real ADS-B benefits for higher performance airplanes may be closer spacing between aircraft allowed by the greater precision of ADS-B compared to radar. Closer spacing may reduce delays and we all benefit from time and fuel savings.

But the requirement for all airplanes in the system to have ADS-B isn’t until January 1, 2020 so spacing reductions cannot happen until after that date. And even then, it will undoubtedly take years for us to notice reduced delays and smoother traffic flow.

ADS-B is a better solution to locating and separating air traffic than ground based radar. That is it’s only real benefit. It will cost airplane owners a bundle to equip with ADS-B, and that’s a fact. Will we see a reduction in delays? Who knows? But I wish the FAA would be more upfront and honest and just say that ADS-B is better, but it shifts cost from the government to the airplane owner. ADS-B is like any tax increase. We hope to get something for it, but for now we can’t be sure. The “free” stuff the FAA is selling just isn’t available to many airplane owners.

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