As you've doubtless heard, Automatic Dependent Surveillance-Broadcast, or ADS-B, long spoken of as the surveillance system of the future, is officially here. In late May the FAA published the final rule, though, fortunately, it will be years before you need to do anything about it.
If you think of ADS-B as being like a transponder, only with possible benefits, you aren't far off. Our ADS-B transmissions will let ATC (air traffic control) and other similarly ADS-B equipped airplanes know where we are, and they will provide additional information, such as altitude, N-number and vertical speed.
It's not just technology for its own sake. There are benefits coming down the road, according to the FAA. Eventually, the agency says, ADS-B will offer services that will benefit every user, but especially the airlines and some business airplanes. Enhancements for more efficient approaches, expedited departures and closer in-trail separation will all, to hear the FAA tell it, increase capacity. For the general aviation community, the traffic management benefits are less glamorous. Eventually, we might see expedited approaches to nonradar airports in low IFR, conditions under which currently only one airplane at a time is cleared for the approach, the so-called "one-in, one-out" rule.
The most basic form of ADS-B will be mandatory by 2020 for all of us who want to fly in the places where we now need a transponder. In the final rule, the FAA decided to mandate just ADS-B Out, which transmits only. (ADS-B In, which requires a display of some kind, allows you to see traffic and to get data-linked graphical weather for free.)
The FAA considered making ADS-B optional for all but the very busiest airspace, a move supported by several alphabet groups, including AOPA (Aircraft Owners and Pilots Association), but the agency rejected that idea in the name of near universal equipage, a key tenet of the plan.
The decision was understandable. The system's most basic and critical function is to keep aircraft separated. ATC's current radar can see primary targets even when their transponders are inoperable or turned off. ADS-B, on the other hand, is completely dependent on an airplane being ADS-B equipped and on that gear being operational. You might know that the requirement for transponders was born of a couple of tragic and horrifying midair collisions between light GA airplanes and airliners, a fact that no one at the FAA has forgotten. So in the end, the FAA erred on the side of requiring ADS-B in as much airspace as it felt it could while still allowing non-ADS-B airplanes to have some airspace to fly in.
As you probably know, the national ADS-B system is already being developed, and ADS-B is in use in a few places in North America, including the Gulf of Mexico, where controllers are using the system, with ground stations installed on oil rigs, for separation of traffic over the Gulf.
The nationwide system is already largely in place along the East Coast, and it will be phased in nationwide over the next several years. As I said, even after the system is complete, operators will have until 2020 to equip their airplanes with ADS-B gear.
The almost decade-long lead time looks to be a good thing, as the architecture of ADS-B, for a variety of technological and nontechnological reasons, has become far more complex than anyone originally envisioned.
If you're confused about what exactly ADS-B is, what it does and what it means to you, don't feel alone. The final rule has created a convoluted, multitier, multitechnology system with primary features that are fundamentally different from the international standard, with other features that have yet to be developed, and with regulatory issues that still need to be ironed out.
While the final rule presented few surprises to insiders, for the rest of us, it provided a better picture of what this new technology is and what it will mean to our flying. It also made clear just how much the vision of ADS-B has changed since its launch 15 years ago.
What exactly ADS-B will mean to our checkbooks is a harder question to answer, though we have some ideas on that subject too.
A Winding Road
The FAA has been talking about ADS-B, or something resembling it, for nearly 40 years, and experimental systems have been under development for close to 15 years. The new surveillance scheme is a critical part of the FAA's NextGen air traffic management system, which seeks to eek more capacity out of the national airspace system, in large part through modernized equipment.
Indeed, the idea that grew into ADS-B was compelling. Instead of radar dishes, the FAA would make use of simple ground stations that would receive automatically generated aircraft position reports and compose them into a near-real-time picture that would allow ATC to do two main things: improve coverage so that airplanes operating even in very remote areas would be under surveillance and improve accuracy to the point that separation could be reduced, allowing more airspace capacity. This latter idea was and is at the center of much of the FAA's NextGen air traffic management plans.
As a bonus, the new system would allow users to get rid of their old transponders, and it would allow them to see traffic and to get weather in the cockpit. Such value-added benefits would motivate owners to equip their airplanes with ADS-B.
Almost none of these things have come to pass, at least not as originally envisioned. We will be required to keep, maintain and turn on our Mode-C or Mode-S transponders. The FAA will have to keep more of its radar dishes than anticipated. And separation benefits will be less than imagined and slower in coming. Perhaps most disappointing is that the broad "radar" coverage we were led to believe ADS-B would provide won't be there. ATC coverage will be comparable to what we have today.
In order to test the technology, the FAA conducted arguably the most radical, large-scale, expensive and successful tests of a technology in FAA history with the grand Alaska Capstone experiment. Capstone began modestly in 1999 in the Ketchikan Peninsula of southeast Alaska and eventually expanded throughout the state. During that time the FAA paid to equip hundreds of publicly and privately owned airplanes with fast-track-certified ADS-B gear and installed an extensive ground station system linked to Alaska air traffic control facilities. The end result was that the FAA was able to provide, for the first time ever in many places, radarlike coverage for airplanes operating in the mountainous Alaska environment. The safety gains, the FAA credibly claims, were impressive.
There is little disagreement that Capstone proved that ADS-B can work, but it also showed the thorny technological and political problems that the FAA would face in defining the nuts and bolts of the system.
Understanding the Two Protocols
In order for ADS-B to work, airplanes need two things: a very accurate navigational source - GPS takes care of that for most of us - and a way to transmit the aircraft's position and other data to the FAA's ground stations. It sounds simple enough, but the selection of the frequency to be used by ADS-B was by far the thorniest problem the FAA faced in developing the system.