Track More Aircraft with Multilateration

Are you interested in learning how you can track even more aircraft with multilateration (MLAT)? If you are not already familiar with MLAT, we provided an introduction in a previous ADS-B blog post.
MLAT lets us track aircraft with older transponders that are not yet equipped with ADS-B. Aircraft with ADS-B continuously transmit their position. For the rest, we have to derive a position by receiving the signals at multiple receiver sites simultaneously (this is how MLAT works).

In order to track more aircraft via MLAT, we need more receiver sites. Your PiAware or FlightFeeder can contribute to MLAT tracking and you will see tracks for these aircraft in SkyAware as a result. However, you need enough nearby neighbor sites that see the same aircraft that you see. This means that each site needs to maximize its range of reception.

Also remember that signals from lower flying aircraft cannot be received as far away as higher flying aircraft. This means that to track lower flying aircraft we need more sites that are (relatively) closer together. Even though you see a lot of green and yellow on our coverage map below, remember that you are primarily seeing coverage above 30,000 feet. Coverage below 30,000 feet is much less and a huge opportunity for further growth of the network.

If you currently have little or no MLAT coverage in your area, there are several reasons why that may be.

• You may not have enough MLAT-capable neighbor sites. You need a PiAware or FlightFeeder to participate in MLAT. MLAT will automatically start working in your area when we have enough sites. Each aircraft must be seen by at least 4 sites simultaneously for MLAT to work.
• Your latitude/longitude position may not be set for your site. Use the gear icon on the "My ADS-B" page to set your position accurately. A missing or inaccurate position for your receiver will prevent you from participating in MLAT.
• The "MLAT enabled" option must be selected in your site settings on the "My ADS-B" page (click the gear icon).
• You need good "timing" data. MLAT positions are calculated based on the time at which you receive a particular aircraft signal. One common reason is that you have your RTL-SDR connected via a low quality USB cable. If this is happening, try connecting your RTL-SDR receiver directly to the USB port on your Raspberry Pi to see if the problem goes away.
• If you are located in Europe or Australia, most aircraft already have ADS-B. (Lucky you!) However, you should remember that there are always exceptions.

How do you tell the number of nearby neighbor sites? There are two ways. One is to zoom-in around your area on our coverage map (remember you need to look at PiAware and FlightFeeder sites). Another way is to look at the "Nearby Sites" list on the "My ADS-B" page at flightaware.com (find the link at the top of any page if you are logged-in).

We hope this information is helpful in getting your site to contribute to MLAT coverage.

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.