Let's talk about the differences between the data types/sources that you see listed in SkyAware(formally Skyview) (for PiAware or FlightFeeder users) or on the My ADS-B statistics page at flightaware.com for all data feeder sites. Specifically, you will see references to ADS-B, MLAT, TIS-B and Other Mode S.
ADS-B is our favorite because this is the data source that directly provides aircraft position information. When you see this in SkyAware, it means the position data came directly from the aircraft in question. On the My ADS-B page, you see statistics that show the number of position messages and aircraft, respectively, that your site received in a particular time interval.
MLAT (short for "multilateration") data is available to PiAware and FlightFeeder sites when you have enough neighbors (at least 3 other sites) that are able to work together to derive a position for an aircraft through mathematical calculat
ions. FlightAware does the math and sends you back the derived position. On the My ADS-B page you will see how many MLAT positions and MLAT-tracked aircraft that were facilitated by your site. (We discussed MLAT specifically in our December 2016 post )
TIS-B ("Traffic Information Service-Broadcast") is position information that is broadcast from an air traffic control ground station. Most sites will not be able to receive these messages because they are sent with a directional signal from the ground pointed toward the sky (typically you need a site at a high elevation or that happens to b
e near a transmitter). TIS-B position reports tend to be intermittently received, if at all, because of the nature of how and when they are transmitted. TIS-B is intended to provide properly equipped aircraft with information about other aircraft flying near them. TIS-B positions can include things such as unidentified primary radar contacts and ground vehicle positions when air traffic control has that data available.
Other Mode S refers to other messages that were successfully received by your site that were not ADS-B or TIS-B, and were not used for an MLAT calculation. This is the data type that we get the most questions about! "Mode S" is the general term for the protocol used to transmit messages such as ADS-B and TIS-B. The primary reason why a message would be classified this way in SkyAware or on the My ADS-B statistics page is because the message was not an ADS-B position message and it was not received by enough sites at the exact same time to be used for MLAT purposes. It is normal to see a portion of your site's messages fall into this category.
Also, note that the data source for a particular aircraft you are viewing in SkyAware may change as more data or different data is received by your site. In particular, it is common for an aircraft to show up first as "Other Mode S" and then change to "MLAT" as FlightAware is able to calculate a position and return that data to your device for display.
For those interested in joining the ADS-B community, FlightAware offers step-by-step instructions to build a PiAware Receiver for under $100.
ADS-B hosts located in areas needing additional coverage might be eligible for a FlightFeeder, a free, prebuilt ADS-B receiver.
FlightAware invites you to join the ADS-B network. You'll become part of a community of aviation hobbyists across the globe and start seeing the skies in a totally different way.