Abstract: A system including a directional antenna that tracks the direction and strength of automatic dependent surveillance-broadcast (ADS-B) messages received using the directional antenna to validate that the digital position information included in the ADS-B messages conforms to the measured and tracked direction and range rate of the source of the ADS-B messages. The system may use existing directional antennae used for airborne collision avoidance systems (ACAS) that are configured to receive transponder responses at 1090 MHz (the same frequency as ADS-B messages) or any other directional antenna able to provide bearing and signal strength. The system of this disclosure may be valuable to validate ADS-B messages transmitted by nearby aircraft that do not include ACAS transponders, such as smaller general aviation (GA) aircraft, some helicopters and some unmanned aerial systems (UAS).