Multilateration (MLAT) Overview

Aircraft without ADS-B transponders do not broadcast their latitude/longitude, so FlightAware uses multilateration of 1090MHz Mode S transponder signals to determine the aircraft's location by using time difference of arrival (TDOA) when an aircraft is detected across three or more receivers/ground stations. Using MLAT, FlightAware can take the aircraft's transponder-provided identification and altitude, then determine the latitude/longitude, and provide real-time flight tracking.

Because an aircraft must be within line-of-sight of three or more FlightAware receivers, MLAT is currently available only in a limited coverage area at this time, unlike our current ADS-B coverage. MLAT positions are effectively real-time, although calculation delays and processing latency is generally 4-6 seconds. FlightAware currently emits up to six MLAT positions per minute per aircraft on the web site.

How it works

MLAT-enabled receivers keep the FlightAware server up to date on which Mode S aircraft are being received. When a particular aircraft is being received from three or more receivers, the server requests sufficient Mode S data from the receiver to sync the time and multilaterate the position of the aircraft. An MLAT-enabled feeder will use approximately 50Kbps of upstream bandwidth while actively contributing to MLAT flight tracking.

Improving Availability of MLAT flight tracks

Both PiAware (v2.0 and above) and FlightFeeder (v7.0 and above) ground stations can currently participate in MLAT and support for additional hardware/software solutions is coming in late 2015. Deploying more receivers in an area will directly improve the ability for FlightAware to generate MLAT positions. For optimal coverage, receivers should be 10-150km apart and in a triangular, square, or circular pattern -- not in a straight line like along a road. Recruiting other people in your general area to host new PiAware or FlightFeeder sites is the best way to grow the availability of FlightAware's MLAT network. As of Wednesday, March 22, 2017, 4,798 receivers are connected and capable of producing MLAT data (view more receiver stats).

Multilateration (MLAT) flight tracking on FlightAware.com

When available, FlightAware's MLAT positions of Mode S aircraft can be seen in the track log alongside regular RADAR, datalink, and projected positions.

For example:

Multilateration (MLAT) positions table

MLAT flight tracking on PiAware

For people running PiAware and connecting directly to the PiAware web server, FlightAware automatically feeds MLAT-derived positions to your PiAware web interface for live MLAT tracking of Mode S aircraft that your receiver and antenna can see. MLAT aircraft are depicted on the map and the chart in purple.

Multilateration (MLAT) positions on dump1090

Multilateration (MLAT) Links