What is this ADS-B Stuff I Keep Hearing About?

You might be surprised to learn that most aircraft have no way of “seeing” other aircraft around them, and the predominant method of avoiding a midair collision is called “see and avoid.” That means pilot try to see other aircraft and avoid running into them. You might also be surprised, even when flying in busy metropolitan areas, that it’s a big sky and you just don’t see that many conflicting aircraft.

However, midair collisions do occur, and in most cases, it’s in beautiful, clear weather near an airport (like the recent collision of two helicopters near Hammonton, New Jersey). Wouldn’t it be better if pilots had some kind of device that would show other aircraft, where they are, and what direction they are going?

Yes, and this technology exists. Airlines and business aircraft are required to carry equipment called TCAS or Traffic Alert and Collision Avoidance System. TCAS can not only show conflicting traffic but a higher-level version can give the pilot guidance on how to climb or descend to avoid a collision. This can be very helpful because TCAS can see other aircraft much more easily than a busy pilot or pilots (in two-pilot aircraft). There is a caveat with TCAS: you must obey the advisory and don’t try to second-guess the system. This has happened, with the result of hundreds of people dying in a collision that shouldn’t have happened. Also, TCAS advisories are inhibited below certain altitudes, which was a factor in the tragic Washington, D.C. midair collision between an Army helicopter and an airliner in January.

But…this is aviation, and everything in aviation is expensive, so the FAA wanted to come up with a system that would be more cost-effective for smaller aircraft, to encourage participation, and that could detect aircraft with a variety of equipment types, to ensure maximum benefit. This turned out to be the awkwardly named ADS-B, which stands for Automatic Dependent Surveillance-Broadcast.

To make sure participation rates were as high as possible in the airspace where it was most needed, the FAA mandated that certain ADS-B equipment be installed in most aircraft by 2020. This mandate is for ADS-B Out, which means it requires that the aircraft owner must install equipment that broadcasts an ADS-B signal that can be seen by other aircraft and detected by Air Traffic Control (ATC) equipment.

ATC’s primary job is to keep aircraft separated, and normally controllers use radar to see where aircraft are and where they are going. Radar works well but doesn’t provide universal coverage. It’s prohibitively expensive to have radar coverage in remote mountainous areas, for example, but much cheaper to install ADS-B ground stations that can fill in those gaps. So now ATC has a better picture of traffic, and so do other aircraft when they are equipped to receive those ADS-B signals.

Luckily, it’s relatively cheap for any pilot to be able to view ADS-B traffic using an iPad and an ADS-B In receiver. The FAA helpfully rebroadcasts traffic information that it gathers via radar, so pilots with ADS-B In can see a lot of traffic on their iPad or on cockpit displays, as many light aircraft, business jets, and some airliners are now being equipped. 

You have probably seen the benefits of ADS-B technology if you’ve ever used a flight tracker such as FlightAware, Flightradar24, ADSBExchange, etc. While ADS-B signals are unencrypted and thus easy to capture, there are processes that the FAA offers to help airplane owners block identifying information in the ADS-B system, and that explains why you might see an airplane on FlightAware without any identification. It’s important for ATC and other pilots to know the position and velocity of the airplane but not who owns and operates the aircraft.