ATC
FAA Cautions about Transponder and ADS-B Testing
In one instance, an ADS-B OUT system ground test created a false airborne target that generated a TCAS resolution advisory on an airliner on approach.

Incidents of improper ground testing of transponder and ADS-B OUT equipment have resulted in false position information, including simulated altitude, being transmitted from the test aircraft and received by aircraft in flight. As a result of these reports, the FAA has issued a Safety Alert For Operators to advise them of the problem and recommend solutions.