Radars… the end is near. Hopefully.

If you are a bird flying over Europe, finding yourself slowly being roasted by radars is not something unexpected. In an effort to achieve radar coverage that is at least double and in view of the fragmented nature of the air traffic management system, this effort has resulted in triple+ coverage in some places. This might be a heart-warming feeling for air traffic controllers and radar manufacturers but for the users of the ATM system, it is more of an expensive overkill than a good thing per se.
Luckily, the time of those expensive, clunky and not too accurate surveillance tools is coming to an end. The replacement? ADS-B.
Automatic Dependent Surveillance – Broadcast is a technology that has been with us for some time now and with the required standards in place, adoption is underway. ADS-B equipped aircraft broadcast their GPS (or other GNSS) derived position and certain other information about once a second. The broadcast information is then received by antennas on the ground and forwarded to air traffic control centers and other users. The data is processed into moving position symbols and labels that look just like traditional radar displays. An important difference is the rate of update. Currently only ground control radars work with such short update cycles, terminal and en-route radars typically provide a 10 second or more update period. Displays being fed by ADS-B data exhibit smooth movement and of course accurate and current information.
Building an ADS-B system, comprising the ground receivers, network and the equipment on board the aircraft is typically cheaper then creating the equivalent surveillance capability with conventional radars. ADS-B offers the added advantage of being deployable in circumstances where radars could never be placed. The antennas are modest in size and fit easily on existing structures, like oil drilling platforms for instance. This characteristic brings surveillance and the associated lower separation minima to areas not previously covered by radar.

The current crop of ADS-B equipment installed on aircraft is able to broadcast position information but is otherwise “deaf”, in other words it is incapable of receiving the transmissions from other aircraft. For this added capability we will need the so-called ADS-B IN feature which will open the door to pilots having their own traffic displays in the cockpit. These can then be used for various airborne separation assistance functions, the real paradigm changers in air traffic management.
An ADS-B system may be cost-efficient (not least because the GPS signals it uses are free and hence the investment in the satellite constellation is not part of the equation) but it provides only a single layer of surveillance while civil aviation requires that there be double coverage. Proponents of radar see this as an opportunity to perpetuate the existence of their beloved monsters but there are better solutions. The issue of alternative timing and positioning for use on the rare occasions when the GPS signal becomes unusable is being considered vigorously and several options are available. You can read more about that here. An important consideration is that the solution ultimately agreed upon should be future proof and cost-effective so that the business case for ADS-B is not killed unnecessarily.
Another issue with ADS-B-based surveillance concerns the apparent ease with which the GPS signal can be spoofed or distorted to the point where it becomes unusable. Tests with unmanned aircraft have shown that it was indeed possible to trick the aircraft avionics to fly into the ground simply by spoofing the GPS signal, but it was not easy to build such a spoofing tool and with a pilot on board, the problem would have been immediately apparent. Making the signals unusable with interference is easier and the tools are readily available.
It is not true however that a person with malicious intent can disable the GPS signals in a whole FIR. Targeting a few aircraft would in fact have an effect not dissimilar to a major radar outage and with appropriate procedures in place, it would not be a major safety risk. With proper alternative timing and positioning, the problem would not pose a safety hazard at all.
ADS-B has shown its value in the Gulf of Mexico, in Alaska, Australia but also in tentative steps in Europe. Now it is time to spread everywhere. The sooner ADS-B can start replacing traditional radar the better. As such, ADS-B can also be one of the vehicles to achieve the Single European Sky objective of substantially reducing the cost of air traffic service provision.