July 23, 2010

Making sense of ADS-B and TIS

With the recent announcement that we'll soon be offering a pair of mode S transponders that can receive TIS traffic, you might have questions about different traffic sources, as well as how ADS-B fits into the mix. Here's a primer on those topics.

ADS-B stands for Automatic Dependant Surveillance – Broadcast. This means it is an automatic system that requires no pilot interaction for the aircraft to broadcast or receive data. It’s dependent on the aircraft being equipped, unlike primary radar which requires no equipment on your aircraft.  And finally, it is a surveillance system because it broadcasts your 3D position and motion vector, allowing ATC and other planes to know the location of your aircraft.

The goal of the ADS-B system is for everyone in the system, pilots and air traffic control alike, to have better knowledge about traffic. You may have heard that ADS-B also supports weather. This is true only in some cases, and is a side benefit of the ADS-B system, not one of the primary goals.
There are two directions of ADS-B: 

  1. ADS-B OUT refers to aircraft broadcasting its position OUT of the airplane.
  2. This is what ATC cares about. It allows them to see airplanes with more accuracy.
  3. Other aircraft can also receive this position even if in an area with no radar coverage.
  4. Can be transmitted via a Mode-S transponder that supports 1090ES in USA and Europe or, via a Universal Access Transceiver (UAT) in the USA only.
  5. Transmitted position is derived from a GPS receiver on the aircraft.
  6. Current regulations require a fully certified, WAAS GPS for ATC to believe the broadcast position.
  7. All aircraft must be equipped by 2015 in Europe and 2020 in USA.
  1. ADS-B IN is what pilots care about. It allows pilots to see other aircraft on in-cockpit traffic displays.
  2. There are ADS-B data products that are potentially available to an aircraft, depending on how it is equipped:
    1. TIS-B is ADS-B traffic
      1. It can be received by aircraft equipped with either a 1090ES receiver or a UAT. TIS-B is not the same as the TIS traffic service that is supported by the Dynon and other available mode S transponders.
    2. FIS-B is ADS-B weather.  
      1. It can only be received by a UAT-equipped aircraft, assuming ground service is available.
  3. When in a radar service area (RSA), the user can see all traffic that ATC can via specialized ADS-B ground stations that transmit this information on both the 1090ES and UAT frequencies.
  4. When not in a RSA, pilot can see ADS-B OUT equipped traffic that is also using the same link type (1090ES or UAT).
An airplane doesn’t need to have both ADS-B IN and ADS-B OUT. A device can support ADS-B IN and ADS-B OUT, but many devices only support one of these functions.

TIS vs TIS-B Traffic

There are other standards such as TIS (Traffic Information Service) which provide ADS-B-like services to pilots, but are NOT part of the ADS-B system. TIS is a USA-only system that requires the aircraft to be in an Radar Service Area (RSA) that also has the right equipment. This is many USA class B and Class C airports.  

What Dynon Supports 

The Dynon SV-XPNDR-261 and SV-XPNDR-262 support ADS-B OUT via 1090ES, as well as TIS. They do not support any ADS-B IN services. They support the display of traffic in the USA via the TIS system. If connected to TSO-C146a certified GPS, they will meet the FAA and European ADS-B OUT requirements.

Dynon's ADS-B Plans

As previously mentioned, the Dynon Transponder modules can support ADS-B OUT via 1090ES, but neither TIS-B nor FIS-B. ADS-B's US coverage is just starting to ramp up, and 2013 is the year that we'll really start seeing national coverage. While we don't have firm plans or anything specific to announce at the moment, do know that it's "on our radar" (sorry). Dynon will support the full suite of ADS-B services in the future.